ATTINY87/167 Automotive Datasheet by Microchip Technology

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Features

●High performance, low power Atmel AVR® 8-bit microcontroller

●Advanced RISC architecture

●123 powerful instructions – most single clock cycle execution

●32 x 8 general purpose working registers

●Fully static operation

●Non-volatile program and data memories

●8K/16Kbyte of in-system programmable (ISP) program memory lash

●endurance: 10,000 write/erase cycles

●512 bytes in-system programmable EEPROM

●endurance: 100,000 write/erase cycles

●512 bytes internal SRAM

●Programming lock for self-programming flash program and EEPROM data

security

●Low size LIN/UART software in-system programmable

●Peripheral features

●LIN 2.1 and 1.3 controller or 8-bit UART (LIN 2.1 certified)

●8-bit asynchronous timer/counter0:

●10-bit clock prescaler

●1 Output compare or 8-bit PWM channel

●16-bit synchronous timer/counter1:

●10-bit clock prescaler

●External event counter

●2 Output compares units or 16-bit PWM channels each driving up to 4 output

pins

●Master/slave SPI serial interface,

●Universal serial interface (USI) with start condition detector (master/slave SPI,

TWI.)

●10-bit ADC:

●11 Single ended channels

●8 Differential ADC channel pairs with programmable gain (8x or 20x)

●On-chip analog comparator with selectable voltage reference

●100µA ±10% current source (LIN node identification)

●On-chip temperature sensor

●Programmable watchdog timer with separate on-chip oscillator

ATtiny87/ATtiny167

8-bit AVR Microcontroller with 8K/16K Bytes In-System

Programmable Flash and LIN Controller

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●Special microcontroller features

●Dynamic clock switching (external/Internal RC/watchdog clock) for power control, EMC reduction

●Debug WIRE on-chip debug (OCD) system

●Hardware in-system programmable (ISP) via SPI port

●External and internal interrupt sources

●Interrupt and wake-up on pin change

●Low power idle, ADC Noise reduction, and power-down modes

●Enhanced power-on reset circuit

●Programmable brown-out detection circuit

●Internal calibrated RC oscillator 8MHz

●4-16MHz and 32KHz crystal/ceramic resonator oscillators

●I/O and packages

●16 programmable I/O lines

●20-pin SOIC, 32-pad QFN and 20-pin TSSOP

●Operating voltage:

●2.7 - 5.5V for ATtiny87/167

●Speed grade:

●0 - 8MHz at 2.7 - 5.5V (automotive temp. range: –40°C to +125°C)

●0 - 16MHz at 4.5 - 5.5V (automotive temp. range: –40°C to +125°C)

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1. Description

1.1 Comparison between Atmel ATtiny87 and ATtiny167

Atmel® ATtiny87 and ATtiny167 are hardware and software compatible. They differ only in memory sizes as shown in

Table 1-1.

1.2 Part Description

The Atmel ATtiny87/167 is a low-power CMOS 8-bit microcontroller based on the AVR® enhanced RISC architecture. By

executing powerful instructions in a single clock cycle, the ATtiny87/167 achieves throughputs approaching 1MIPS per MHz

allowing the system designer to optimize power consumption versus processing speed.

The AVR core combines a rich instruction set with 32 general purpose working registers. All the 32 registers are directly

connected to the arithmetic logic unit (ALU), allowing two independent registers to be accessed in one single instruction

executed in one clock cycle. The resulting architecture is more code efficient while achieving throughputs up to ten times

faster than conventional CISC microcontrollers.

The Atmel ATtiny87/167 provides the following features: 8K/16Kbyte of in-system programmable flash, 512 bytes EEPROM,

512 bytes SRAM, 16 general purpose I/O lines, 32 general purpose working registers, one 8-bit timer/counter with compare

modes, one 8-bit high speed timer/counter, universal serial interface, a LIN controller, internal and external interrupts, a

11-channel, 10-bit ADC, a programmable watchdog timer with internal oscillator, and three software selectable power saving

modes. The idle mode stops the CPU while allowing the SRAM, timer/counter, ADC, analog comparator, and interrupt

system to continue functioning. The power-down mode saves the register contents, disabling all chip functions until the next

interrupt or hardware reset. The ADC noise reduction mode stops the CPU and all I/O modules except ADC, to minimize

switching noise during ADC conversions.

The device is manufactured using Atmel’s high density non-volatile memory technology. The on-chip ISP flash allows the

program memory to be re-programmed in-system through an SPI serial interface, by a conventional non-volatile memory

programmer or by an on-chip boot code running on the AVR core. The Boot program can use any interface to download the

application program in the Flash memory. By combining an 8-bit RISC CPU with In-System Self-Programmable Flash on a

monolithic chip, the Atmel ATtiny87/167 is a powerful microcontroller that provides a highly flexible and cost effective

solution to many embedded control applications.

The Atmel ATtiny87/167 AVR is supported with a full suite of program and system development tools including: C compilers,

macro assemblers, program debugger/simulators, in-circuit emulators, and evaluation kits.

Table 1-1. Memory Size Summary

Device Flash EEPROM SRAM Interrupt Vector size

ATtiny167 16Kbytes 512 Bytes 512 Bytes 2-instruction-words/vector

ATtiny87 8Kbytes 512 Bytes 512 Bytes 2-instruction-words/vector

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1.3 Automotive Quality Grade

The Atmel® ATtiny87/167 have been developed and manufactured according to the most stringent requirements of the

international standard ISO-TS-16949. This data sheet contains limit values extracted from the results of extensive

characterization (temperature and voltage). The quality and reliability of the Atmel ATtiny87/167 have been verified during

regular product qualification as per AEC-Q100 grade 1.

As indicated in the ordering information paragraph, this document refers only to grade 1 products, for grade 0 products refer

to appendix A.

1.4 Disclaimer

Typical values contained in this data sheet are based on simulations and characterization of other AVR® microcontrollers

manufactured on the same process technology. Min. and Max values will be available after the device is characterized.

Table 1-2. Temperature Grade Identification for Automotive Products

Temperature

Identifier Comments

–40°C/+125°C ZGrade 1

–40°C/+150°C DGrade 0

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1.5 Block Diagram

Figure 1-1. Block Diagram

Power

Supervision

POR/ BOD

and

RESET

Oscillator

Circuits/

Clock

Generation

Watchdog

Timer

Watchdog

Oscillator

Program

Logic

debugWIRE

AVR

CPU

EEPROM

DATA BUS

Flash

GND VCC

A/D Conv.

Internal

Voltage

References

Timer/

Counter-1

Timer/

Counter-0

Analog

Comp.

SPI and USI

PORT B (8) PORT A (8) LIN/ UART

SRAM

AVCC

AGND

RESET

XTAL[1;2]

PB[0..7] PA[0..7]

3333:3333: C o CEEEECEECE E_I:I_E_I:I_E_I_ oz

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1.6 Pin Configuration

Figure 1-2. Pinout ATtiny87/167 - SOIC20 and TSSOP20

Figure 1-3. Pinout ATtiny87/167 - QFN32

(RXLIN/RXD/ADC0/PCINT0) PA0

(MISO/DO/OC0A/ADC2/PCINT2) PA2

(TXLIN/TXD/ADC1/PCINT1) PA1

(INT1/ISRC/ADC3/PCINT3) PA3

AVCC

AGND

(MOSI/SDA/DI/ICP1/ADC4/PCINT4) PA4

(SCK/SCL/USCK/T1/ADC5/PCINT5) PA5

(SS/AIN0/ADC6/PCINT6) PA6

(AREF/XREF/AIN1/ADC7/PCINT7) PA7

20-pin

Top

view

PB0 (PCINT8/OC1AU/DI/SDA)

PB1 (PCINT9/OC1BU/DO)

PB3 (PCINT11/OC1BV)

PB4 (PCINT12/OC1AW/XTAL1/CLKI)

PB6 (PCINT14/ADC9/OC1AX/INT0)

PB7 (PCINT15/ADC10/OC1BX/RESET/dW)

PB5 (PCINT13/ADC8/OC1BW/XTAL2/CLKO)

GND

VCC

PB2 (PCINT10/OC1AV/USCK/SCL)

PA2 (PCINT2/ADC2/OC0A/DO/MISO)

PA1 (PCINT1/ADC1/TXD/TXLIN)

PA0 (PCINT0/ADC0/RXD/RXLIN)

PB0 (PCINT8/OC1AU/DI/SDA)

PB1 (PCINT9/OC1BU/DO)

PB2 (PCINT10/OC1AV/USCK/SCL)

PB3 (PCINT11/OC1BV)

(MOSI/SDA/DI/ICP1/ADC4/PCINT4) PA4

(SCK/SCL/USCK/T1/ADC5/PCINT5) PA5

(SS/AIN0/ADC6/PCINT6) PA6

(AREF/XREF/AIN1/ADC7/PCINT7) PA7

(dW/RESET/OC1BX/ADC10/PCINT15) PB7

(INT0/OC1AX/ADC9/PCINT14) PB6

GND

VCC

PB4 (PCINT12/OC1AW/XTAL1/CLKI)

PB5 (PCINT13/ADC8/OC1BW/XTAL2/CLKO)

(INT1/ISRC/ADC3/PCINT3) PA3

Index Corner

Bottom pad should be

soldered to ground

AVCC

AGND

31 30 29 28 27 26 25

9 10111213141516

32-lead

Top view

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1.7 Pin Description

1.7.1 Vcc

Supply voltage.

1.7.2 GND

Ground.

1.7.3 AVcc

Analog supply voltage.

1.7.4 AGND

Analog ground.

1.7.5 Port A (PA7..PA0)

Port A is an 8-bit bi-directional I/O port with internal pull-up resistors (selected for each bit). The Port A output buffers have

symmetrical drive characteristics with both high sink and source capability. As inputs, Port A pins that are externally pulled

low will source current if the pull-up resistors are activated. The Port A pins are tri-stated when a reset condition becomes

active, even if the clock is not running.

Port A also serves the functions of various special features of the Atmel® ATtiny87/167 as listed on Section 9.3.3 “Alternate

Functions of Port A” on page 73.

1.7.6 Port B (PB7..PB0)

Port B is an 8-bit bi-directional I/O port with internal pull-up resistors (selected for each bit). The Port B output buffers have

symmetrical drive characteristics with both high sink and source capability. As inputs, Port B pins that are externally pulled

low will source current if the pull-up resistors are activated. The Port B pins are tri-stated when a reset condition becomes

active, even if the clock is not running.

Port B also serves the functions of various special features of the ATtiny87/167 as listed on Section 9.3.4 “Alternate

Functions of Port B” on page 78.

1.8 Resources

A comprehensive set of development tools, application notes and datasheets are available for download on

http://www.atmel.com/avr.

1.9 About Code Examples

This documentation contains simple code examples that briefly show how to use various parts of the device. These code

examples assume that the part specific header file is included before compilation. Be aware that not all C compiler vendors

include bit definitions in the header files and interrupt handling in C is compiler dependent. Please confirm with the C

compiler documentation for more details.

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2. AVR CPU Core

2.1 Overview

This section discusses the AVR® core architecture in general. The main function of the CPU core is to ensure correct

program execution. The CPU must therefore be able to access memories, perform calculations, control peripherals, and

handle interrupts.

Figure 2-1. Block Diagram of the AVR Architecture

In order to maximize performance and parallelism, the AVR uses a Harvard architecture – with separate memories and

buses for program and data. Instructions in the program memory are executed with a single level pipelining. While one

instruction is being executed, the next instruction is pre-fetched from the program memory. This concept enables instructions

to be executed in every clock cycle. The program memory is in-system reprogrammable flash memory. The fast-access

register file contains 32 x 8-bit general purpose working registers with a single clock cycle access time. This allows single-

cycle arithmetic logic unit (ALU) operation. In a typical ALU operation, two operands are output from the register file, the

operation is executed, and the result is stored back in the register file – in one clock cycle.

Six of the 32 registers can be used as three 16-bit indirect address register pointers for data space addressing – enabling

efficient address calculations. One of the these address pointers can also be used as an address pointer for look up tables in

flash program memory. These added function registers are the 16-bit X-, Y-, and Z-register, described later in this section.

The ALU supports arithmetic and logic operations between registers or between a constant and a register. Single register

operations can also be executed in the ALU. After an arithmetic operation, the status register is updated to reflect

information about the result of the operation.

Status and

Control

Interrupt

Unit

32 x 8

General

Purpose

Registers

ALU

Data Bus 8-bit

Data

SRAM

Watchdog

Timer

Instruction

Decoder

Analog

Comparator

EEPROM

I/O Lines

I/O Module n

Control Lines

Direct Addressing

Indirect Addressing

I/O Module 2

I/O Module 1

A.D.C.

Program

Counter

Flash

Program

Memory

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Program flow is provided by conditional and unconditional jump and call instructions, able to directly address the whole

address space. Most AVR® instructions have a single 16-bit word format. Every program memory address contains a 16- or

32-bit instruction.

During interrupts and subroutine calls, the return address program counter (PC) is stored on the stack. The stack is

effectively allocated in the general data SRAM, and consequently the stack size is only limited by the total SRAM size and

the usage of the SRAM. All user programs must initialize the SP in the reset routine (before subroutines or interrupts are

executed). The stack pointer (SP) is read/write accessible in the I/O space. The data SRAM can easily be accessed through

the five different addressing modes supported in the AVR architecture.

The memory spaces in the AVR architecture are all linear and regular memory maps.

A flexible interrupt module has its control registers in the I/O space with an additional global interrupt enable bit in the status

register. All interrupts have a separate interrupt vector in the interrupt vector table. The interrupts have priority in accordance

with their interrupt vector position. The lower the interrupt vector address, the higher the priority.

The I/O memory space contains 64 addresses for CPU peripheral functions as control registers, SPI, and other I/O functions.

The I/O memory can be accessed directly, or as the data space locations following those of the register file, 0x20 - 0x5F.

2.2 ALU – Arithmetic Logic Unit

The high-performance AVR ALU operates in direct connection with all the 32 general purpose working registers. Within a

single clock cycle, arithmetic operations between general purpose registers or between a register and an immediate are

executed. The ALU operations are divided into three main categories – arithmetic, logical, and bit-functions. Some

implementations of the architecture also provide a powerful multiplier supporting both signed/unsigned multiplication and

fractional format. See the “instruction set” section for a detailed description.

2.3 Status Register

The status register contains information about the result of the most recently executed arithmetic instruction. This

information can be used for altering program flow in order to perform conditional operations. Note that the status register is

updated after all ALU operations, as specified in the instruction set reference. This will in many cases remove the need for

using the dedicated compare instructions, resulting in faster and more compact code.

The status egister is not automatically stored when entering an interrupt routine and restored when returning from an

interrupt. This must be handled by software.

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2.3.1 SREG – AVR Status Register

The AVR® Status Register – SREG – is defined as:

• Bit 7 – I: Global Interrupt Enable

The global interrupt enable bit must be set for the interrupts to be enabled. The individual interrupt enable control is then

performed in separate control registers. If the global interrupt enable register is cleared, none of the interrupts are enabled

independent of the individual interrupt enable settings. The I-bit is cleared by hardware after an interrupt has occurred, and is

set by the RETI instruction to enable subsequent interrupts. The I-bit can also be set and cleared by the application with the

SEI and CLI instructions, as described in the instruction set reference.

• Bit 6 – T: Bit Copy Storage

The bit copy instructions BLD (Bit LoaD) and BST (Bit STore) use the T-bit as source or destination for the operated bit. A bit

from a register in the register file can be copied into T by the BST instruction, and a bit in T can be copied into a bit in a

• Bit 5 – H: Half Carry Flag

The half carry flag H indicates a half carry in some arithmetic operations. Half carry is useful in BCD arithmetic. See the

“instruction set description” for detailed information.

• Bit 4 – S: Sign Bit, S = N V

The S-bit is always an exclusive or between the negative flag N and the two’s complement overflow flag V. See the

“instruction set description” for detailed information.

• Bit 3 – V: Two’s Complement Overflow Flag

The two’s complement overflow flag V supports two’s complement arithmetics. See the “instruction set description” for

detailed information.

• Bit 2 – N: Negative Flag

The negative flag N indicates a negative result in an arithmetic or logic operation. See the “instruction set description” for

detailed information.

• Bit 1 – Z: Zero Flag

The zero flag Z indicates a zero result in an arithmetic or logic operation. See the “instruction set description” for detailed

information.

• Bit 0 – C: Carry Flag

The carry flag C indicates a carry in an arithmetic or logic operation. See the “instruction set description” for detailed

information.

Bit 76543210

I T H S V N Z C SREG

Read/Write R/W R/W R/W R/W R/W R/W R/W R/W

Initial Value00000000

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2.4 General Purpose Register File

The register file is optimized for the AVR® enhanced RISC instruction set. In order to achieve the required performance and

flexibility, the following input/output schemes are supported by the register file:

●One 8-bit output operand and one 8-bit result input

●Two 8-bit output operands and one 8-bit result input

●Two 8-bit output operands and one 16-bit result input

●One 16-bit output operand and one 16-bit result input

Figure 2-2 shows the structure of the 32 general purpose working registers in the CPU.

Figure 2-2. AVR CPU General Purpose Working Registers

Most of the instructions operating on the register file have direct access to all registers, and most of them are single cycle

instructions.

As shown in Figure 2-2, each register is also assigned a data memory address, mapping them directly into the first 32

locations of the user data space. Although not being physically implemented as SRAM locations, this memory organization

provides great flexibility in access of the registers, as the X-, Y- and Z-pointer registers can be set to index any register in the

file.

2.4.1 The X-register, Y-register, and Z-register

The registers R26.R31 have some added functions to their general purpose usage. These registers are 16-bit address

pointers for indirect addressing of the data space. The three indirect address registers X, Y, and Z are defined as described

in Figure 2-3 on page 12.

70Addr.

R0 0x00

R1 0x01

R2 0x02

…

R13 0x0D

General R14 0x0E

Purpose R15 0x0F

Working R16 0x10

Registers R17 0x11

…

R26 0x1A X-register Low Byte

R27 0x1B X-register High Byte

R28 0x1C Y-register Low Byte

R29 0x1D Y-register High Byte

R30 0x1E Z-register Low Byte

R31 0x1F Z-register High Byte

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Figure 2-3. The X-, Y-, and Z-registers

In the different addressing modes these address registers have functions as fixed displacement, automatic increment, and

automatic decrement (see the instruction set reference for details).

2.5 Stack Pointer

The stack is mainly used for storing temporary data, for storing local variables and for storing return addresses after

interrupts and subroutine calls. The stack pointer register always points to the top of the stack. Note that the stack is

implemented as growing from higher memory locations to lower memory locations. This implies that a stack PUSH command

decreases the stack pointer.

The stack pointer points to the data SRAM Stack area where the subroutine and interrupt stacks are located. This stack

space in the data SRAM must be defined by the program before any subroutine calls are executed or interrupts are enabled.

The stack pointer must be set to point above 0x60. The stack pointer is decremented by one when data is pushed onto the

stack with the PUSH instruction, and it is decremented by two when the return address is pushed onto the stack with

subroutine call or interrupt. The stack pointer is incremented by one when data is popped from the stack with the POP

instruction, and it is incremented by two when data is popped from the stack with return from subroutine RET or return from

interrupt RETI.

The AVR® stack pointer is implemented as two 8-bit registers in the I/O space. The number of bits actually used is

implementation dependent. Note that the data space in some implementations of the AVR architecture is so small that only

SPL is needed. In this case, the SPH register will not be present

2.5.1 SPH and SPL – Stack Pointer Register

15 XH XL 0

X-register 7 0 7 0

R27 (0x1B) R26 (0x1A)

15 YH YL 0

Y-register 7 0 7 0

R29 (0x1D) R28 (0x1C)

15 ZH ZL 0

Z-register 7 0 7 0

R31 (0x1F) R30 (0x1E)

Bit 151413121110 9 8

SP15 SP14 SP13 SP12 SP11 SP10 SP9 SP8 SPH

SP7 SP6 SP5 SP4 SP3 SP2 SP1 SP0 SPL

76543210

Read/Write R/W R/W R/W R/W R/W R/W R/W R/W

R/W R/W R/W R/W R/W R/W R/W R/W

Initial Value ISRAM end (See Table 3-1 on page 16)

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2.6 Instruction Execution Timing

This section describes the general access timing concepts for instruction execution. The AVR® CPU is driven by the CPU

clock clkCPU, directly generated from the selected clock source for the chip. No internal clock division is used.

Figure 2-4 shows the parallel instruction fetches and instruction executions enabled by the Harvard architecture and the fast

access register file concept. This is the basic pipelining concept to obtain up to 1MIPS per MHz with the corresponding

unique results for functions per cost, functions per clocks, and functions per power-unit.

Figure 2-4. The Parallel Instruction Fetches and Instruction Executions

Figure 2-5 shows the internal timing concept for the register file. In a single clock cycle an ALU operation using two register

operands is executed, and the result is stored back to the destination register.

Figure 2-5. Single Cycle ALU Operation

2.7 Reset and Interrupt Handling

The AVR provides several different interrupt sources. These interrupts and the separate Reset Vector each have a separate

program vector in the program memory space. All interrupts are assigned individual enable bits which must be written logic

one together with the global interrupt enable bit in the status register in order to enable the interrupt.

The lowest addresses in the program memory space are by default defined as the reset and interrupt vectors. The complete

list of vectors is shown in Section 7. “Interrupts” on page 57. The list also determines the priority levels of the different

interrupts. The lower the address the higher is the priority level. RESET has the highest priority, and next is INT0 – the

external interrupt request 0.

clkCPU

1st Instruction Fetch

1st Instruction Execute

2nd Instruction Fetch

T1 T2 T3 T4

2nd Instruction Execute

3rd Instruction Fetch

3rd Instruction Execute

4th Instruction Fetch

clkCPU

Result Write Back

ALU Operation Execute

Total Execution Time

T2 T3 T4

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2.7.1 Interrupt Behavior

When an interrupt occurs, the global interrupt enable I-bit is cleared and all interrupts are disabled. The user software can

write logic one to the I-bit to enable nested interrupts. All enabled interrupts can then interrupt the current interrupt routine.

The I-bit is automatically set when a return from interrupt instruction – RETI – is executed.

There are basically two types of interrupts. The first type is triggered by an event that sets the interrupt flag. For these

interrupts, the program counter is vectored to the actual interrupt vector in order to execute the interrupt handling routine,

and hardware clears the corresponding interrupt flag. Interrupt flags can also be cleared by writing a logic one to the flag bit

position(s) to be cleared. If an interrupt condition occurs while the corresponding interrupt enable bit is cleared, the interrupt

flag will be set and remembered until the interrupt is enabled, or the flag is cleared by software. Similarly, if one or more

interrupt conditions occur while the global interrupt enable bit is cleared, the corresponding interrupt flag(s) will be set and

remembered until the global interrupt enable bit is set, and will then be executed by order of priority.

The second type of interrupts will trigger as long as the interrupt condition is present. These interrupts do not necessarily

have interrupt flags. If the interrupt condition disappears before the interrupt is enabled, the interrupt will not be triggered.

When the AVR® exits from an interrupt, it will always return to the main program and execute one more instruction before

any pending interrupt is served.

Note that the status register is not automatically stored when entering an interrupt routine, nor restored when returning from

an interrupt routine. This must be handled by software.

When using the CLI instruction to disable interrupts, the interrupts will be immediately disabled. No interrupt will be executed

after the CLI instruction, even if it occurs simultaneously with the CLI instruction. The following example shows how this can

be used to avoid interrupts during the timed EEPROM write sequence.

When using the SEI instruction to enable interrupts, the instruction following SEI will be executed before any pending

interrupts, as shown in this example.

Assembly Code Example

in r16, SREG ; store SREG value

cli ; disable interrupts during timed sequence

sbi EECR, EEMPE ; start EEPROM write

sbi EECR, EEPE

out SREG, r16 ; restore SREG value (I-bit)

C Code Example

char cSREG;

cSREG = SREG; /* store SREG value */

/* disable interrupts during timed sequence */

_CLI();

EECR |= (1<<EEMPE); /* start EEPROM write */

EECR |= (1<<EEPE);

SREG = cSREG; /* restore SREG value (I-bit) */

Assembly Code Example

sei ; set Global Interrupt Enable

sleep ; enter sleep, waiting for interrupt

; note: will enter sleep before any pending

; interrupt(s)

C Code Example

_SEI(); /* set Global Interrupt Enable */

_SLEEP(); /* enter sleep, waiting for interrupt */

/* note: will enter sleep before any pending interrupt(s) */

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2.7.2 Interrupt Response Time

The interrupt execution response for all the enabled AVR® interrupts is four clock cycles minimum. After four clock cycles the

program vector address for the actual interrupt handling routine is executed. During this four clock cycle period, the program

counter is pushed onto the stack. The vector is normally a jump to the interrupt routine, and this jump takes three clock

cycles. If an interrupt occurs during execution of a multi-cycle instruction, this instruction is completed before the interrupt is

served. If an interrupt occurs when the MCU is in sleep mode, the interrupt execution response time is increased by four

clock cycles. This increase comes in addition to the start-up time from the selected sleep mode.

A return from an interrupt handling routine takes four clock cycles. During these four clock cycles, the program counter (two

bytes) is popped back from the stack, the stack pointer is incremented by two, and the I-bit in SREG is set.

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3. AVR Memories

This section describes the different memories in the Atmel® ATtiny87/167. The AVR® architecture has two main memory

spaces, the data memory and the program memory space. In addition, the Atmel ATtiny87/167 features an EEPROM

memory for data storage. All three memory spaces are linear and regular.

3.1 In-system Re-programmable Flash Program Memory

The Atmel ATtiny87/167 contains on-chip in-system reprogrammable flash memory for program storage (see “flash size” in

Table 3-1 on page 16). Since all AVR instructions are 16 or 32 bits wide, the flash is organized as 16 bits wide. ATtiny87/167

does not have separate boot loader and application program sections, and the SPM instruction can be executed from the

entire flash. See SELFPRGEN description in Section 20.2.1 “Store Program Memory Control and Status Register –

SPMCSR” on page 202 for more details.

The flash memory has an endurance of at least 10,000 write/erase cycles in automotive range. The Atmel ATtiny87/167

program counter (PC) address the program memory locations. Section 21. “Memory Programming” on page 207 contains a

detailed description on flash data serial downloading using the SPI pins.

Constant tables can be allocated within the entire program memory address space (see the LPM – load program memory

instruction description).

Timing diagrams for instruction fetch and execution are presented in Section 2.6 “Instruction Execution Timing” on page 13.

Table 3-1. Memory Mapping.

Memory Mnemonic ATtiny87 ATtiny167

Flash

Size Flash size 8Kbytes 16Kbytes

Start Address -0x0000

End Address Flash end 0x1FFF(1)

0x0FFF(2)

0x3FFF(1)

0x1FFF(2)

32 Registers

Size -32 bytes

Start Address -0x0000

End Address -0x001F

I/O

Registers

Size -64 bytes

Start Address -0x0020

End Address -0x005F

Ext I/O

Registers

Size -160 bytes

Start Address -0x0060

End Address -0x00FF

Internal

SRAM

Size ISRAM size 512 bytes

Start Address ISRAM start 0x0100

End Address ISRAM end 0x02FF

EEPROM

Size E2 size 512 bytes

Start Address -0x0000

End Address E2 end 0x01FF

Notes: 1. Byte address.

2. Word (16-bit) address.

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Figure 3-1. Program Memory Map

3.2 SRAM Data Memory

Figure 3-2 shows how the Atmel® ATtiny87/167 SRAM memory is organized.

The ATtiny87/167 is a complex microcontroller with more peripheral units than can be supported within the 64 locations

reserved in the opcode for the IN and OUT instructions. For the extended I/O space in SRAM, only the ST/STS/STD and

LD/LDS/LDD instructions can be used.

The data memory locations address both the register file, the I/O memory, extended I/O memory, and the internal data

SRAM. The first 32 locations address the register file, the next 64 location the standard I/O memory, then 160 locations of

extended I/O memory, and the next locations address the internal data SRAM (see “ISRAM size” in Table 3-1 on page 16).

The five different addressing modes for the data memory cover: direct, indirect with displacement, indirect, indirect with pre-

decrement, and indirect with post-increment. In the register file, registers R26 to R31 feature the indirect addressing pointer

registers.

The direct addressing reaches the entire data space.

The indirect with displacement mode reaches 63 address locations from the base address given by the Y- or Z-register.

When using register indirect addressing modes with automatic pre-decrement and post-increment, the address registers X,

Y, and Z are decremented or incremented.

The 32 general purpose working registers, 64 I/O Registers, 160 extended I/O registers and the internal data SRAM in the

ATtiny87/167 are all accessible through all these addressing modes. The register file is described in Section 2.4 “General

Purpose Register File” on page 11.

Figure 3-2. Data Memory Map

0x0000

Flash end

Program Memory

32 Registers

Data Memory

0x0000 - 0x001F

0x0020 - 0x005F

0x0060 - 0x00FF

ISRAM start

ISRAM end

64 I/O Registers

160 Ext I/O Registers

Internal SRAM

(ISRAM size)

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3.2.1 Data Memory Access Times

This section describes the general access timing concepts for internal memory access. The internal data SRAM access is

performed in two clkCPU cycles as described in Figure 3-3.

Figure 3-3. On-chip Data SRAM Access Cycles

3.3 EEPROM Data Memory

The Atmel® ATtiny87/167 contains EEPROM memory (see “E2 size” in Table 3-1 on page 16). It is organized as a separate

data space, in which single bytes can be read and written. The EEPROM has an endurance of at least 100,000 write/erase

cycles in automotive range. The access between the EEPROM and the CPU is described in the following, specifying the

EEPROM address registers, the EEPROM data register and the EEPROM control register.

Section 21. “Memory Programming” on page 207 contains a detailed description on EEPROM programming in SPI or

parallel programming mode.

3.3.1 EEPROM Read/Write Access

The EEPROM access registers are accessible in the I/O space.

The write access times for the EEPROM are given in Table 3-2. A self-timing function, however, lets the user software detect

when the next byte can be written. If the user code contains instructions that write the EEPROM, some precautions must be

taken. In heavily filtered power supplies, Vcc is likely to rise or fall slowly on power-up/down. This causes the device for

some period of time to run at a voltage lower than specified as minimum for the clock frequency used. See Section 3.3.6

“Preventing EEPROM Corruption” on page 21 for details on how to avoid problems in these situations.

In order to prevent unintentional EEPROM writes, a specific write procedure must be followed. Refer to Section 3.3.2

“Atomic Byte Programming” on page 18 and Section 3.3.3 “Split Byte Programming” on page 19 for details on this.

When the EEPROM is read, the CPU is halted for four clock cycles before the next instruction is executed. When the

EEPROM is written, the CPU is halted for two clock cycles before the next instruction is executed.

3.3.2 Atomic Byte Programming

Using atomic byte programming is the simplest mode. When writing a byte to the EEPROM, the user must write the address

into the EEARL register and data into EEDR register. If the EEPMn bits are zero, writing EEPE (within four cycles after

EEMPE is written) will trigger the erase/write operation. Both the erase and write cycle are done in one operation and the

total programming time is given in Table 1. The EEPE bit remains set until the erase and write operations are completed.

While the device is busy with programming, it is not possible to do any other EEPROM operations.

clk

CPU

Data

Address validCompute Address

Next Instruction

Write

Read

Memory Access Instruction

ddress

T2 T3

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3.3.3 Split Byte Programming

It is possible to split the erase and write cycle in two different operations. This may be useful if the system requires short

access time for some limited period of time (typically if the power supply voltage falls). In order to take advantage of this

method, it is required that the locations to be written have been erased before the write operation. But since the erase and

write operations are split, it is possible to do the erase operations when the system allows doing time-critical operations

(typically after power-up).

3.3.4 Erase

To erase a byte, the address must be written to EEAR. If the EEPMn bits are 0b01, writing the EEPE (within four cycles after

EEMPE is written) will trigger the erase operation only (programming time is given in Table 1). The EEPE bit remains set

until the erase operation completes. While the device is busy programming, it is not possible to do any other EEPROM

operations.

3.3.5 Write

To write a location, the user must write the address into EEAR and the data into EEDR. If the EEPMn bits are 0b10, writing

the EEPE (within four cycles after EEMPE is written) will trigger the write operation only (programming time is given in table

1). The EEPE bit remains set until the write operation completes. If the location to be written has not been erased before

write, the data that is stored must be considered as lost. While the device is busy with programming, it is not possible to do

any other EEPROM operations.

The calibrated oscillator is used to time the EEPROM accesses. Make sure the oscillator frequency is within the

requirements described in Section 4.5.1 “OSCCAL – Oscillator Calibration Register” on page 38.

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The following code examples show one assembly and one C function for erase, write, or atomic write of the EEPROM. The

examples assume that interrupts are controlled (e.g., by disabling interrupts globally) so that no interrupts will occur during

execution of these functions.

Assembly Code Example

EEPROM_write:

; Wait for completion of previous write

sbic EECR,EEPE

rjmp EEPROM_write

; Set Programming mode

ldi r16, (0<<EEPM1)|(0<<EEPM0)

out EECR, r16

; Set up address (r18:r17) in address register

out EEARH, r18

out EEARL, r17

; Write data (r16) to data register

out EEDR, r16

; Write logical one to EEMPE

sbi EECR,EEMPE

; Start eeprom write by setting EEPE

sbi EECR,EEPE

ret

C Code Example

void EEPROM_write(unsigned char ucAddress, unsigned char ucData)

{

/* Wait for completion of previous write */

while(EECR & (1<<EEPE))

;

/* Set Programming mode */

EECR = (0<<EEPM1)|(0<<EEPM0);

/* Set up address and data registers */

EEAR = ucAddress;

EEDR = ucData;

/* Write logical one to EEMPE */

EECR |= (1<<EEMPE);

/* Start eeprom write by setting EEPE */

EECR |= (1<<EEPE);

}

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The next code examples show assembly and C functions for reading the EEPROM. The examples assume that interrupts

are controlled so that no interrupts will occur during execution of these functions.

3.3.6 Preventing EEPROM Corruption

During periods of low Vcc, the EEPROM data can be corrupted because the supply voltage is too low for the CPU and the

EEPROM to operate properly. These issues are the same as for board level systems using EEPROM, and the same design

solutions should be applied.

An EEPROM data corruption can be caused by two situations when the voltage is too low. First, a regular write sequence to

the EEPROM requires a minimum voltage to operate correctly. Secondly, the CPU itself can execute instructions incorrectly,

if the supply voltage is too low.

EEPROM data corruption can easily be avoided by following this design recommendation:

Keep the AVR RESET active (low) during periods of insufficient power supply voltage. This can be done by enabling the

internal Brown-out Detector (BOD). If the detection level of the internal BOD does not match the needed detection level, an

external low Vcc reset protection circuit can be used. If a reset occurs while a write operation is in progress, the write

operation will be completed provided that the power supply voltage is sufficient.

Assembly Code Example

EEPROM_read:

; Wait for completion of previous write

sbic EECR,EEPE

rjmp EEPROM_read

; Set up address (r18:r17) in address register

out EEARH, r18

out EEARL, r17

; Start eeprom read by writing EERE

sbi EECR,EERE

; Read data from data register

in r16,EEDR

ret

C Code Example

unsigned char EEPROM_read(unsigned char ucAddress)

{

/* Wait for completion of previous write */

while(EECR & (1<<EEPE))

;

/* Set up address register */

EEAR = ucAddress;

/* Start eeprom read by writing EERE */

EECR |= (1<<EERE);

/* Return data from data register */

return EEDR;

}

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3.4 I/O Memory

The I/O space definition of the Atmel® ATtiny87/167 is shown in Section “” on page 243.

All ATtiny87/167 I/Os and peripherals are placed in the I/O space. All I/O locations may be accessed by the LD/LDS/LDD

and ST/STS/STD instructions, transferring data between the 32 general purpose working registers and the I/O space. I/O

registers within the address range 0x00 - 0x1F are directly bit-accessible using the SBI and CBI instructions. In these

registers, the value of single bits can be checked by using the SBIS and SBIC instructions. Refer to the instruction set

section for more details. When using the I/O specific commands IN and OUT, the I/O addresses 0x00 - 0x3F must be used.

When addressing I/O registers as data space using LD and ST instructions, 0x20 must be added to these addresses. The

Atmel ATtiny87/167 is a complex microcontroller with more peripheral units than can be supported within the 64 location

reserved in opcode for the IN and OUT instructions. For the extended I/O space from 0x60 - 0xFF in SRAM, only the

ST/STS/STD and LD/LDS/LDD instructions can be used.

For compatibility with future devices, reserved bits should be written to zero if accessed. Reserved I/O memory addresses

should never be written.

Some of the status flags are cleared by writing a logical one to them. Note that, unlike most other AVRs, the CBI and SBI

instructions will only operate on the specified bit, and can therefore be used on registers containing such status flags. The

CBI and SBI instructions work with registers 0x00 to 0x1F only.

The I/O and peripherals control registers are explained in later sections.

3.4.1 General Purpose I/O Registers

The Atmel ATtiny87/167 contains three general purpose I/O registers. These registers can be used for storing any

information, and they are particularly useful for storing global variables and status flags.

The general purpose I/O registers within the address range 0x00 - 0x1F are directly bit-accessible using the SBI, CBI, SBIS,

and SBIC instructions.

3.5 Register Description

3.5.1 EEARH and EEARL – EEPROM Address Register

• Bit 7:1 – Reserved Bits

These bits are reserved for future use and will always read as 0 in ATtiny87/167.

• Bits 8:0 – EEAR8:0: EEPROM Address

The EEPROM address registers – EEARH and EEARL – specifies the high EEPROM address in the EEPROM space (see

“E2 size” in Table 3-1 on page 16). The EEPROM data bytes are addressed linearly between 0 and “E2 size”. The initial

value of EEAR is undefined. A proper value must be written before the EEPROM may be accessed.

Note: For information only - ATtiny47: EEAR8 exists as register bit but it is not used for addressing.

Bit 76543210

-------EEAR8EEARH

EEAR7 EEAR6 EEAR5 EEAR4 EEAR3 EEAR2 EEAR1 EEAR0 EEARL

Bit 76543210

Read/Write RRRRRRRR/W

Read/Write R/W R/W R/W R/W R/W R/W R/W R/W

Initial Value0000000X

Initial Value X X X X X X X X

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3.5.2 EEDR – EEPROM Data Register

• Bits 7:0 – EEDR7:0: EEPROM Data

For the EEPROM write operation the EEDR register contains the data to be written to the EEPROM in the address given by

the EEAR register. For the EEPROM read operation, the EEDR contains the data read out from the EEPROM at the address

given by EEAR.

3.5.3 EECR – EEPROM Control Register

• Bit 7,6 – Res: Reserved Bits

These bits are reserved for future use and will always read as 0 in ATtiny87/167. After reading, mask out these bits. For

compatibility with future AVR® devices, always write these bits to zero.

• Bits 5, 4 – EEPM1 and EEPM0: EEPROM Programming Mode Bits

The EEPROM programming mode bits setting defines which programming action that will be triggered when writing EEPE. It

is possible to program data in one atomic operation (erase the old value and program the new value) or to split the erase and

write operations in two different operations. The programming times for the different modes are shown in Table 3-2. While

EEPE is set, any write to EEPMn will be ignored. During reset, the EEPMn bits will be reset to 0b00 unless the EEPROM is

busy programming.

• Bit 3 – EERIE: EEPROM Ready Interrupt Enable

Writing EERIE to one enables the EEPROM ready interrupt if the I-bit in SREG is set. Writing EERIE to zero disables the

interrupt. The EEPROM ready interrupt generates a constant interrupt when Non-volatile memory is ready for programming.

• Bit 2 – EEMPE: EEPROM Master Program Enable

The EEMPE bit determines whether writing EEPE to one will have effect or not.

When EEMPE is set, setting EEPE within four clock cycles will program the EEPROM at the selected address. If EEMPE is

zero, setting EEPE will have no effect. When EEMPE has been written to one by software, hardware clears the bit to zero

after four clock cycles.

Bit 76543210

EEDR7 EEDR6 EEDR5 EEDR4 EEDR3 EEDR2 EEDR1 EEDR0 EEDR

Read/Write R/W R/W R/W R/W R/W R/W R/W R/W

Initial Value00000000

Bit 76543210

– – EEPM1 EEPM0 EERIE EEMPE EEPE EERE EECR

Read/Write R R R/W R/W R/W R/W R/W R/W

Initial Value 0 0 X X 0 0 X 0

Table 3-2. EEPROM Mode Bits

EEPM1 EEPM0

Typical Programming

Time Operation

0 0 3.4ms Erase and write in one operation (atomic operation)

0 1 1.8ms Erase only

1 0 1.8ms Write only

1 1 – Reserved for future use

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• Bit 1 – EEPE: EEPROM Program Enable

The EEPROM program enable signal EEPE is the programming enable signal to the EEPROM. When EEPE is written, the

EEPROM will be programmed according to the EEPMn bits setting. The EEMPE bit must be written to one before a logical

one is written to EEPE, otherwise no EEPROM write takes place. When the write access time has elapsed, the EEPE bit is

cleared by hardware. When EEPE has been set, the CPU is halted for two cycles before the next instruction is executed.

• Bit 0 – EERE: EEPROM Read Enable

The EEPROM read enable signal – EERE – is the read strobe to the EEPROM. When the correct address is set up in the

EEAR register, the EERE bit must be written to one to trigger the EEPROM read. The EEPROM read access takes one

instruction, and the requested data is available immediately. When the EEPROM is read, the CPU is halted for four cycles

before the next instruction is executed. The user should poll the EEPE bit before starting the read operation. If a write

operation is in progress, it is neither possible to read the EEPROM, nor to change the EEAR register.

3.5.4 General Purpose I/O Register 2 – GPIOR2

3.5.5 General Purpose I/O Register 1 – GPIOR1

3.5.6 General Purpose I/O Register 0 – GPIOR0

Bit 76543210

GPIOR27 GPIOR26 GPIOR25 GPIOR24 GPIOR23 GPIOR22 GPIOR21 GPIOR20 GPIOR2

Read/Write R/W R/W R/W R/W R/W R/W R/W R/W

Initial Value00000000

Bit 76543210

GPIOR17 GPIOR16 GPIOR15 GPIOR14 GPIOR13 GPIOR12 GPIOR11 GPIOR10 GPIOR1

Read/Write R/W R/W R/W R/W R/W R/W R/W R/W

Initial Value00000000

Bit 76543210

GPIOR07 GPIOR06 GPIOR05 GPIOR04 GPIOR03 GPIOR02 GPIOR01 GPIOR00 GPIOR0

Read/Write R/W R/W R/W R/W R/W R/W R/W R/W

Initial Value00000000

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4. System Clock and Clock Options

The Atmel® ATtiny87/167 provides a large number of clock sources. They can be divided into two categories: internal and

external. Some external clock sources can be shared with the asynchronous timer. After reset, the clock source is

determined by the CKSEL Fuses. Once the device is running, software clock switching is possible to any other clock

sources.

Hardware controls are provided for clock switching management but some specific procedures must be observed. Clock

switching should be performed with caution as some settings could result in the device having an incorrect configuration.

4.1 Clock Systems and their Distribution

Figure 4-1 presents the principal clock systems in the AVR® and their distribution. All of the clocks may not need to be active

at any given time. In order to reduce power consumption, the clocks to modules not being used can be halted by using

different sleep modes or by using features of the dynamic clock switch circuit (See Section 5. “Power Management and

Sleep Modes” on page 42 and Section 4.3 “Dynamic Clock Switch” on page 32). The clock systems are detailed below.

Figure 4-1. Clock Distribution

Asynchronous

Timer/Counter0

Flash and

EEPROM

Calibrated RC

Oscillator

Low-frequency

Crystal Oscillator

Crystal

Oscillator

Watchdog

Oscillator

Prescaler

CKOUT

Fuse

Multiplexer

PB4/XTAL1/CLKI PB5/XTAL2/CLKO

General I/O

AVR Clock

Control Unit

ADC

External Clock

CPU Core

Source clock Watchdog clock

RAM

Reset Logic Watchdog Timer

clkI/O

clkASY

clkCPU

clkADC

clkFLASH

Clock Switch

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4.1.1 CPU Clock – clkCPU

The CPU clock is routed to parts of the system concerned with the AVR® core operation. Examples of such modules are the

general purpose register file, the status register and the data memory holding the stack pointer. Halting the CPU clock

inhibits the core from performing general operations and calculations.

4.1.2 I/O Clock – clkI/O

The I/O clock is used by the majority of the I/O modules, like synchronous timer/counter. The I/O clock is also used by the

external interrupt module, but note that some external interrupts are detected by asynchronous logic, allowing such

interrupts to be detected even if the I/O clock is halted.

4.1.3 Flash Clock – clkFLASH

The flash clock controls operation of the flash interface. The flash clock is usually active simultaneously with the CPU clock.

4.1.4 Asynchronous Timer Clock – clkASY

The asynchronous timer clock allows the asynchronous timer/counter to be clocked directly from an external clock or an

external low frequency crystal. The dedicated clock domain allows using this timer/counter as a real-time counter even when

the device is in sleep mode.

4.1.5 ADC Clock – clkADC

The ADC is provided with a dedicated clock domain. This allows halting the CPU and I/O clocks in order to reduce noise

generated by digital circuitry. This gives more accurate ADC conversion results.

4.2 Clock Sources

The device has the following clock source options, selectable by flash fuse bits (default) or by the CLKSELR register

(dynamic clock switch circuit) as shown below. The clock from the selected source is input to the AVR clock generator, and

routed to the appropriate modules.

Table 4-1. Device Clocking Options Select(1) versus PB4 and PB5 Functionality

Device Clocking Option

CKSEL3..0 (2)

CSEL3..0 (3) PB4 PB5

External Clock 0000 bCLKI CLKO - I/O

Calibrated Internal RC Oscillator 8.0MHz 0010 bI/O CLKO - I/O

Watchdog Oscillator 128kHz 0011 bI/O CLKO - I/O

External Low-frequency Oscillator 01xx bXTAL1 XTAL2

External Crystal/Ceramic Resonator (0.4 - 0.9MHz) 100x bXTAL1 XTAL2

External Crystal/Ceramic Resonator (0.9 - 3.0MHz) 101x bXTAL1 XTAL2

External Crystal/Ceramic Resonator (3.0 - 8.0MHz) 110x bXTAL1 XTAL2

External Crystal/Ceramic Resonator (8.0 - 16.0MHz) 111x bXTAL1 XTAL2

Notes: 1. For all fuses “1” means unprogrammed while “0” means programmed.

2. Flash fuse bits.

3. CLKSELR register bits.

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The various choices for each clocking option are given in the following sections.

When the CPU wakes up from power-down or power-save, or when a new clock source is enabled by the dynamic clock

switch circuit, the selected clock source is used to time the start-up, ensuring stable oscillator operation before instruction

execution starts.

When the CPU starts from reset, there is an additional delay allowing the power to reach a stable level before commencing

normal operation. The watchdog oscillator is used for timing this real-time part of the start-up sequence. The number of WDT

oscillator cycles used for each time-out is shown in Table 4-2

4.2.1 Default Clock Source

At reset, the CKSEL and SUT fuse settings are copied into the CLKSELR register. The device will then use the clock source

and the start-up timings defined by the CLKSELR bits (CSEL3.0 and CSUT1:0).

The device is shipped with CKSEL fuses = 0010 b, SUT fuses = 10 b, and CKDIV8 fuse programmed. The default clock

source setting is therefore the internal RC oscillator running at 8MHz with the longest start-up time and an initial system

clock divided by 8. This default setting ensures that all users can make their desired clock source setting using an in-system

or high-voltage programmer. This set-up must be taken into account when using ISP tools.

4.2.2 Calibrated Internal RC Oscillator

By default, the internal RC oscillator provides an approximate 8.0MHz clock. Though voltage and temperature dependent,

this clock can be accurately calibrated by the user. See Table 22-1 on page 224 and Section 24.7 “Internal Oscillator Speed”

on page 240 for more details.

If selected, it can operate without external components. At reset, hardware loads the pre-programmed calibration value into

the OSCCAL register and thereby automatically configuring the RC oscillator. The accuracy of this calibration is shown as

factory calibration in Table 22-1 on page 224.

By adjusting the OSCCAL register in software, see Section 4.5.1 “OSCCAL – Oscillator Calibration Register” on page 38, it

is possible to get a higher calibration accuracy than by using the factory calibration. The accuracy of this calibration is shown

as User calibration in Table 22-1 on page 224.

The watchdog oscillator will still be used for the watchdog timer and for the reset time-out even when this oscillator is used

as the device clock. For more information on the pre-programmed calibration value, see Section 21.4 “Calibration Byte” on

page 209.

Table 4-2. Number of Watchdog Oscillator Cycles

Typ. Time-out

(Vcc = 5.0V)

Typ. Time-out

(Vcc = 5.0V)

Number of Cycles

4.1ms 4.3ms 512

65ms 69ms 8K(8,192)

— — Nmes: 1. BMHz frequenm/ exceeds xhe specificaxion of xhe devxce (depends on Vcc). the CKDIVB [use can be pro- Nmes: 1. Flashfusebhs Nmes: 1. Flashfusebhs AtmeL

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When this oscillator is selected, start-up times are determined by the SUT Fuses or by CSUT field as shown in Table 4-4.

4.2.3 128KHz Internal Oscillator

The 128KHz internal oscillator is a low power oscillator providing a clock of 128KHz. The frequency is nominal at 3V and

25°C. This clock may be selected as the system clock by programming CKSEL fuses or CSEL field as shown in Table 4-1 on

page 26.

When this clock source is selected, start-up times are determined by the SUT Fuses or by CSUT field as shown in Table 4-5 .

Table 4-3. Internal Calibrated RC Oscillator Operating Modes(1)

Frequency Range(2) (MHz)

CKSEL3..0(3)(4)

CSEL3..0(5)

7.6 - 8.4 0010

Notes: 1. 8MHz frequency exceeds the specification of the device (depends on Vcc), the CKDIV8 fuse can be pro-

grammed in order to divide the internal frequency by 8.

2. The frequency ranges are guideline values.

3. The device is shipped with this CKSEL = “0010”.

4. Flash Fuse bits.

5. CLKSELR register bits.

Table 4-4. Start-up Times for the Internal Calibrated RC Oscillator Clock Selection

SUT1..0(1)

CSUT1..0(2)

Start-up Time from

Power-down/save

Additional Delay from Reset

(Vcc = 5.0V) Recommended Usage

00(3) 6CK 14CK BOD enabled

01 6CK 14CK + 4.1ms Fast rising power

10(4) 6CK 14CK + 65ms Slowly rising power

11 Reserved

Notes: 1. Flash fuse bits

2. CLKSELR register bits1

3. This setting is only available if RSTDISBL fuse is not set

4. The device is shipped with this option selected.

Table 4-5. Start-up Times for the 128 kHz Internal Oscillator

SUT1..0(1)

CSUT1..0(2)

Start-up Time from

Power-down/save

Additional Delay

from Reset

(Vcc = 5.0V)

Recommended Usage

00(3) 6CK 14CK BOD enabled

01 6CK 14CK + 4.1ms Fast rising power

10 6CK 14CK + 65ms Slowly rising power

11 Reserved

Notes: 1. Flash fuse bits

2. CLKSELR register bits

3. This setting is only available if RSTDISBL fuse is not set

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4.2.4 Crystal Oscillator

XTAL1 and XTAL2 are input and output, respectively, of an inverting amplifier which can be configured for use as an on-chip

oscillator, as shown in Figure 4-2. Either a quartz crystal or a ceramic resonator may be used.

C1 and C2 should always be equal for both crystals and resonators. The optimal value of the capacitors depends on the

crystal or resonator in use, the amount of stray capacitance, and the electromagnetic noise of the environment. Some initial

guidelines for choosing capacitors for use with crystals are given in Table 4-6. For ceramic resonators, the capacitor values

given by the manufacturer should be used.

Figure 4-2. Crystal Oscillator Connections

The oscillator can operate in three different modes, each optimized for a specific frequency range. The operating mode is

selected by CKSEL3..1 fuses or by CSEL3..1 field as shown in Table 4-6.

Table 4-6. Crystal Oscillator Operating Modes

CKSEL3..1(1)

CSEL3..1(2) Frequency Range (MHz)

Recommended Range for Capacitors

C1 and C2 for Use with Crystals (pF)

100(3) 0.4 - 0.9 –

101 0.9 - 3.0 12 - 22

110 3.0 - 8.0 12 - 22

111 8.0 - 16.0 12 - 22

Notes: 1. Flash fuse bits.

2. CLKSELR register bits.

3. This option should not be used with crystals, only with ceramic resonators.

XTAL2

XTAL1

GND

Notes: 1. Flashfusebits. AtmeL

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The CKSEL0 fuse together with the SUT1..0 Fuses or CSEL0 together with CSUT1..0 field select the start-up times as

shown in Table 4-7.

Table 4-7. Start-up Times for the Crystal Oscillator Clock Selection

CKSEL0(1)

CSEL0(2)

SUT1..0(1)

CSUT1..0(2)

Start-up Time from

Power-down/save

Additional Delay

from Reset

(Vcc = 5.0V) Recommended Usage

000 258CK(3) 14CK + 4.1ms Ceramic resonator, fast

rising power

001 258CK(3) 14CK + 65ms Ceramic resonator, slowly

rising power

010(5) 1K(1024)CK(4) 14CK Ceramic resonator, BOD

enabled

011 1K(1024)CK(4) 14CK + 4.1ms Ceramic resonator, fast

rising power

100 1K(1024)CK(4) 14CK + 65ms Ceramic resonator, slowly

rising power

101(5) 16K(16384)CK 14CK Crystal Oscillator, BOD

enabled

110 16K(16384)CK 14CK + 4.1ms Crystal Oscillator, fast

rising power

111 16K(16384)CK 14CK + 65ms Crystal Oscillator, slowly

rising power

Notes: 1. Flash fuse bits.

2. CLKSELR register bits.

3. These options should only be used when not operating close to the maximum frequency of the device, and

only if frequency stability at start-up is not important for the application. These options are not suitable for

crystals.

4. These options are intended for use with ceramic resonators and will ensure frequency stability at start-up.

They can also be used with crystals when not operating close to the maximum frequency of the device, and if

frequency stability at start-up is not important for the application.

5. This setting is only available if RSTDISBL fuse is not set.

i i H Notes: 1. Flashfusebits. AtmeL

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4.2.5 Low-frequency Crystal Oscillator

To use a 32.768kHz watch crystal as the clock source for the device, the low-frequency crystal oscillator must be selected by

setting CKSEL fuses or CSEL field as shown in Table 4-1 on page 26. The crystal should be connected as shown in Figure

4-3. Refer to the 32.768 kHz crystal oscillator application note for details on oscillator operation and how to choose

appropriate values for C1 and C2.

The 32.768kHz watch crystal oscillator can be used by the asynchronous timer if the (high-frequency) crystal oscillator is not

running or if the external clock is not enabled (Section 4.3.3 “Enable/Disable Clock Source” on page 33). The asynchronous

timer is then able to start itself this low-frequency crystal oscillator.

Figure 4-3. Low-frequency Crystal Oscillator Connections

When this oscillator is selected, start-up times are determined by the SUT fuses or by CSUT field as shown in Table 4-8.

4.2.6 External Clock

To drive the device from this external clock source, CLKI should be driven as shown in Figure 4-4. To run the device on an

external clock, the CKSEL Fuses or CSEL field must be programmed as shown in Table 4-1 on page 26.

Figure 4-4. External Clock Drive Configuration

Table 4-8. Start-up Times for the Low Frequency Crystal Oscillator Clock Selection

SUT1..0(1)

CSUT1..0(2)

Start-up Time from

Power-down/save

Additional Delay from

Reset (Vcc = 5.0V) Recommended usage

00 1K(1024)CK(3) 4.1ms Fast rising power or BOD enabled

01 1K(1024)CK(3) 65ms Slowly rising power

10 32K(32768)CK 65ms Stable frequency at start-up

11 Reserved

Notes: 1. Flash fuse bits.

2. CLKSELR register bits.

3. These options should only be used if frequency stability at start-up is not important for the application.

C1 = 12 to 22pF

C2 = 12 to 22pF

12 to 22pF capacitors may be necessary if parasitic

impedance (pads, wires and PCB) is very low.

XTAL2

32.768KHz

XTAL1

GND

(XTAL2)

(CLKO)

CLKI

(XTAL1)

GND

External

Clock

Signal

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When this clock source is selected, start-up times are determined by the SUT Fuses or CSUT field as shown in Table 4-9.

This external clock can be used by the asynchronous timer if the high or low frequency crystal oscillator is not running

(Section 4.3.3 “Enable/Disable Clock Source” on page 33). The asynchronous timer is then able to enable this input.

Note that the system clock prescaler can be used to implement run-time changes of the internal clock frequency while still

ensuring stable operation. Refer to Section 4.4 “System Clock Prescaler” on page 38 for details.

4.2.7 Clock Output Buffer

If not using a crystal oscillator, the device can output the system clock on the CLKO pin. To enable the output, the CKOUT

fuse or COUT bit of CLKSELR register has to be programmed. This option is useful when the device clock is needed to drive

other circuits on the system. Note that the clock will not be output during reset and the normal operation of I/O pin will be

overridden when the fuses are programmed. If the System clock prescaler is used, it is the divided system clock that is

output.

4.3 Dynamic Clock Switch

4.3.1 Features

The Atmel® ATtiny87/167 provides a powerful dynamic clock switch circuit that allows users to turn on and off clocks of the

device on the fly. The built-in de-glitching circuitry allows clocks to be enabled or disabled asynchronously. This enables

efficient power management schemes to be implemented easily and quickly. In a safety application, the dynamic clock

switch circuit allows continuous monitoring of the external clock permitting a fallback scheme in case of clock failure.

The control of the dynamic clock switch circuit must be supervised by software. This operation is facilitated by the following

features:

●Safe commands, to avoid unintentional commands, a special write procedure must be followed to change the

CLKCSR register bits (Section 4.5.2 “CLKPR – Clock Prescaler Register” on page 38):

●Exclusive action, the actions are controlled by a decoding table (commands) written to the CLKCSR register. This

ensures that only one command operation can be launched at any time. The main actions of the decoding table are:

●‘Disable Clock Source’,

●‘Enable Clock Source’,

●‘Request Clock Availability’,

●‘Clock Source Switching’,

●‘Recover System Clock Source’,

●‘Enable Watchdog in Automatic Reload Mode’.

●Command status return. The ‘request clock availability ’ command returns status via the CLKRDY bit in the

CLKCSR register. The ‘recover system clock source ’ command returns a code of the current clock source in the

CLKSELR register. This information is used in the supervisory software routines as shown in Section 4.3.7 on page

34.

Table 4-9. Start-up Times for the External Clock Selection

SUT1..0(1)

CSUT1..0(2)

Start-up Time from

Power-down/save

Additional Delay from Reset

(Vcc = 5.0V)

Recommended Usage

00 6CK 14CK (+ 4.1ms(3))BOD enabled

01 6CK 14CK + 4.1ms Fast rising power

10 6CK 14CK + 65ms Slowly rising power

11 Reserved

Notes: 1. Flash fuse bits.

2. CLKSELR register bits.

3. Additional delay (+ 4ms) available if RSTDISBL fuse is set.

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4.3.2 CLKSELR Register

4.3.2.1 Fuses Substitution

At reset, bits of the low fuse byte are copied into the CLKSELR register. The content of this register can subsequently be

user modified to overwrite the default values from the low fuse byte. CKSEL3..0, SUT1..0 and CKOUT fuses correspond

respectively to CSEL3..0, CSUT1:0 and ~(COUT) bits of the CLKSELR register as shown in Figure 4-5 on page 33.

4.3.2.2 Source Selection

The available codes of clock source are given in Table 4-1 on page 26.

Figure 4-5. Fuses substitution and Clock Source Selection

The CLKSELR register contains the CSEL, CSUT and COUT values which will be used by the ‘enable/disable clock source’,

‘request for clock availability’ or ‘clock source switching’ commands.

4.3.2.3 Source Recovering

The ‘recover system clock source’ command updates the CKSEL field of CLKSELR register (Section 4.3.6 “System Clock

Source Recovering” on page 34).

4.3.3 Enable/Disable Clock Source

The ‘enable clock source’ command selects and enables a clock source configured by the settings in the CLKSELR register.

CSEL3..0 will select the clock source and CSUT1:0 will select the start-up time (just as CKSEL and SUT fuse bits do). To be

sure that a clock source is operating, the ‘request for clock availability’ command must be executed after the ‘enable clock

source’ command. This will indicate via the CLKRDY bit in the CLKCSR register that a valid clock source is available and

operational.

The ‘disable clock source’ command disables the clock source indicated by the settings of CLKSELR register (only

CSEL3..0). If the clock source indicated is currently the one that is used to drive the system clock, the command is not

executed.

Because the selected configuration is latched at clock source level, it is possible to enable many clock sources at a given

time (ex: the internal RC oscillator for system clock + an oscillator with external crystal). The user (code) is responsible of

this management.

4.3.4 COUT Command

The ‘CKOUT ’ command allows to drive the CLKO pin. Refer to Section 4.2.7 “Clock Output Buffer” on page 32 for using.

Internal

Data Bus

Fuse:

Fuse Low Byte

CLKSELR

Selected

Configuration

Clock

Switch

Current

Configuration

Reset

CLKSEL[3..0]

SUT[1..0]

CKOUT

CSEL[3..0]

CSUT[1..0]

COUT

SEL

Decoder

SCLKRq

(*)

SCLKRq

(*)

:Command of Clock Control and Status Register

CKSEL[3..0]

EN-0

CKOUT

EN-1

EN-2

EN-n

SEL-0

SEL-1

SEL-2

SEL-n

SEL

Encoder

SUT[1..0]

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4.3.5 Clock Availability

‘Request for clock availability’ command enables a hardware oscillation cycle counter driven by the selected source clock,

CSEL3..0. The count limit value is determined by the settings of CSUT1..0. The clock is declared ready (CLKRDY = 1) when

the count limit value is reached. The CLKRDY flag is reset when the count starts. Once set, this flag remains unchanged

until a new count is commanded. To perform this checking, the CKSEL and CSUT fields should not be changed while the

operation is running.

Note that once the new clock source is selected (‘enable clock source’ command), the count procedure is automatically

started. The user (code) should wait for the setting of the CLKRDY flag in CLKSCR register before using a newly selected

clock.

At any time, the user (code) can ask for the availability of a clock source. The user (code) can request it by writing the

‘request for clock availability ’ command in the CLKSCR register. A full polling of the status of clock sources can thus be

done.

4.3.6 System Clock Source Recovering

The ‘recover system clock source’ command returns the current clock source used to drive the system clock as per

Table 4-1 on page 26. The CKSEL field of CLKSELR register is then updated with this returned value. There is no

information on the SUT used or status on CKOUT.

4.3.7 Clock Switching

To drive the system clock, the user can switch from the current clock source to any other of the following ones (one of them

being the current clock source):

1. Calibrated internal RC oscillator 8.0MHz,

2. Internal watchdog oscillator 128kHz,

3. External clock,

4. External low-frequency oscillator,

5. External Crystal/Ceramic Resonator.

The clock switching is performed by a sequence of commands. First, the user (code) must make sure that the new clock

source is operating. Then the ‘clock source switching’ command can be issued. Once this command has been successfully

completed using the ‘recover system clock source’ command, the user (code) may stop the previous clock source.

It is strongly recommended to run this sequence only once the interrupts have been disabled. The user (code) is responsible

for the correct implementation of the clock switching sequence.

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Here is a “light” C-code that describes such a sequence of commands.

Warning: In the Atmel® ATtiny87/167, only one among the three external clock sources can be enabled at a given time.

Moreover, the enables of the external clock and of the external low-frequency oscillator are shared with the

asynchronous timer.

C Code Example

void ClockSwiching (unsigned char clk_number, unsigned char sut) {

#define CLOCK_RECOVER 0x05

#define CLOCK_ENABLE 0x02

#define CLOCK_SWITCH 0x04

#define CLOCK_DISABLE 0x01

unsigned char previous_clk, temp;

// Disable interrupts

temp = SREG; asm ("cli");

// Save the current system clock source

CLKCSR = 1 << CLKCCE;

CLKCSR = CLOCK_RECOVER;

previous_clk = CLKSELR & 0x0F;

// Enable the new clock source

CLKSELR = ((sut << 4 ) & 0x30) | (clk_number & 0x0F);

CLKCSR = 1 << CLKCCE;

CLKCSR = CLOCK_ENABLE;

// Wait for clock validity

while ((CLKCSR & (1 << CLKRDY)) == 0);

// Switch clock source

CLKCSR = 1 << CLKCCE;

CLKCSR = CLOCK_SWITCH;

// Wait for effective switching

while (1){

CLKCSR = 1 << CLKCCE;

CLKCSR = CLOCK_RECOVER;

if ((CLKSELR & 0x0F) == (clk_number & 0x0F)) break;

}

// Shut down unneeded clock source

if (previous_clk != (clk_number & 0x0F)) {

CLKSELR = previous_clk;

CLKCSR = 1 << CLKCCE;

CLKCSR = CLOCK_DISABLE;

}

// Re-enable interrupts

SREG = temp;

}

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4.3.8 Clock Monitoring

A safe system needs to monitor its clock sources. Two domains need to be monitored:

●Clock sources for peripherals,

●Clocks sources for system clock generation.

In the first domain, the user (code) can easily check the validity of the clock(s) (Section 4.3.4 “COUT Command” on page

33). In the second domain, the lack of a clock results in the code not running. Thus, the presence of the system clock needs

to be monitored by hardware.

Using the on-chip watchdog allows this monitoring. Normally, the watchdog reloading is performed only if the code reaches

some specific software labels, reaching these labels proves that the system clock is running. Otherwise the watchdog reset

is enabled. This behavior can be considered as a clock monitoring.

If the standard watchdog functionality is not desired, the Atmel® ATtiny87/167 watchdog permits the system clock to be

monitored without having to resort to the complexity of a full software watchdog handler. The solution proposed in the

ATtiny87/167 is to automate the watchdog reloading with only one command, at the beginning of the session.

So, to monitor the system clock, the user will have two options:

1. Using the standard watchdog features (software reload),

2. Or using the automatic reloading (hardware reload).

The two options are exclusive.

Warning: These two options make sense only if the clock source at RESET is an internal source. The fuse settings

determine this operation.

Figure 4-6. Watchdog Timer with Automatic Reloading

The ‘enable watchdog in automatic reload mode’ command has priority over the standard watchdog enabling. In this mode,

only the reset function of the watchdog is enabled (no more watchdog interrupt). The WDP3..0 bits of the WDTCSR register

always determine the watchdog timer prescaling.

As the watchdog will not be active before executing the ‘enable watchdog in automatic reload mode’ command, it is

recommended to activate this command before switching to an external clock source (See note on page 36).

Notes: 1. Only the reset (watchdog reset included) disables this function. The watchdog system reset flag (WDRF bit of

MCUSR register) can be used to monitor the reset cause.

2. Only clock frequencies greater than or equal to (4 * watchDog clock frequency) can be monitored.

Internal Bus

WDTCSR

Watchdog

Checker

Reload

Watchdog Clock

Automatic

Reolading

Mode

System CLK

Enable

Interrupt

Reset

WDP

[3 to 0]

WDE

WDIF

WDIE

CLKCSR : WD ARL ENABLE- AtmeL

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Here is a “light” C-code of a clock switching function using automatic clock monitoring.

C Code Example

void ClockSwiching (unsigned char clk_number, unsigned char sut) {

#define CLOCK_RECOVER 0x05

#define CLOCK_ENABLE 0x02

#define CLOCK_SWITCH 0x04

#define CLOCK_DISABLE 0x01

#define WD_ARL_ENABLE 0x06

#define WD_2048CYCLES 0x07

unsigned char previous_clk, temp;

// Disable interrupts

temp = SREG; asm ("cli");

// Save the current system clock source

CLKCSR = 1 << CLKCCE;

CLKCSR = CLOCK_RECOVER;

previous_clk = CLKSELR & 0x0F;

// Enable the new clock source

CLKSELR = ((sut << 4 ) & 0x30) | (clk_number & 0x0F);

CLKCSR = 1 << CLKCCE;

CLKCSR = CLOCK_ENABLE;

// Wait for clock validity

while ((CLKCSR & (1 << CLKRDY)) == 0);

// Switch clock source

CLKCSR = 1 << CLKCCE;

CLKCSR = CLOCK_SWITCH;

// Wait for effective switching

while (1){

CLKCSR = 1 << CLKCCE;

CLKCSR = CLOCK_RECOVER;

if ((CLKSELR & 0x0F) == (clk_number & 0x0F)) break;

}

// Shut down unneeded clock source

if (previous_clk != (clk_number & 0x0F)) {

CLKSELR = previous_clk;

CLKCSR = 1 << CLKCCE;

CLKCSR = CLOCK_DISABLE;

}

// Re-enable interrupts

SREG = temp;

}

// Enable the watchdog in automatic reload mode

WDTCSR = (1 << WDCE) | (1 << WDE);

WDTCSR = (1 << WDE ) | WD_2048CYCLES;

CLKCSR = 1 << CLKCCE;

CLKCSR = WD_ARL_ENABLE;

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4.4 System Clock Prescaler

4.4.1 Features

The Atmel® ATtiny87/167 system clock can be divided by setting the clock prescaler register – CLKPR. This feature can be

used to decrease power consumption when the requirement for processing power is low. This can be used with all clock

source options, and it will affect the clock frequency of the CPU and all synchronous peripherals. clkI/O, clkADC, clkCPU, and

clkFLASH are divided by a factor as shown in Table 4-10 on page 39.

4.4.2 Switching Time

When switching between prescaler settings, the system clock prescaler ensures that no glitches occur in the clock system

and that no intermediate frequency is higher than neither the clock frequency corresponding to the previous setting, nor the

clock frequency corresponding to the new setting.

The ripple counter that implements the prescaler runs at the frequency of the undivided clock, which may be faster than the

CPU’s clock frequency. Hence, it is not possible to determine the state of the prescaler – even if it were readable, and the

exact time it takes to switch from one clock division to another cannot be exactly predicted.

From the time the CLKPS values are written, it takes between T1 + T2 and T1 + 2*T2 before the new clock frequency is

active. In this interval, 2 active clock edges are produced. Here, T1 is the previous clock period, and T2 is the period

corresponding to the new prescaler setting.

4.5 Register Description

4.5.1 OSCCAL – Oscillator Calibration Register

• Bits 7:0 – CAL7:0: Oscillator Calibration Value

The oscillator calibration register is used to trim the calibrated internal RC oscillator to remove process variations from the

oscillator frequency. The factory-calibrated value is automatically written to this register during chip reset, giving an oscillator

frequency of 8.0MHz at 25°C. The application software can write this register to change the oscillator frequency. The

oscillator can be calibrated to any frequency in the range 7.3 - 8.1MHz within ±2% accuracy. Calibration outside that range is

not guaranteed.

Note that this oscillator is used to time EEPROM and flash write accesses, and these write times will be affected accordingly.

If the EEPROM or flash are written, do not calibrate to more than 8.8MHz. Otherwise, the EEPROM or flash write may fail.

The CAL7 bit determines the range of operation for the oscillator. Setting this bit to 0 gives the lowest frequency range,

setting this bit to 1 gives the highest frequency range. The two frequency ranges are overlapping, in other words a setting of

OSCCAL = 0x7F gives a higher frequency than OSCCAL = 0x80.

The CAL6..0 bits are used to tune the frequency within the selected range. A setting of 0x00 gives the lowest frequency in

that range, and a setting of 0x7F gives the highest frequency in the range. Incrementing CAL6..0 by 1 will give a frequency

increment of less than 2% in the frequency range 7.3 - 8.1MHz.

4.5.2 CLKPR – Clock Prescaler Register

Bit 76543210

CAL7 CAL6 CAL5 CAL4 CAL3 CAL2 CAL1 CAL0 OSCCAL

Read/Write R/W R/W R/W R/W R/W R/W R/W R/W

Initial Value Device Specific Calibration Value

Bit 76543210

CLKPCE – – – CLKPS3 CLKPS2 CLKPS1 CLKPS0 CLKPR

Read/Write R/W R R R R/W R/W R/W R/W

Initial Value 0 0 0 0 See Bit Description

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• Bit 7 – CLKPCE: Clock Prescaler Change Enable

The CLKPCE bit must be written to logic one to enable change of the CLKPS bits. The CLKPCE bit is only updated when the

other bits in CLKPR are simultaneously written to zero. CLKPCE is cleared by hardware four cycles after it is written or when

the CLKPS bits are written. Rewriting the CLKPCE bit within this time-out period does neither extend the time-out period, nor

clear the CLKPCE bit.

• Bits 6:4 – Res: Reserved Bits

These bits are reserved bits in the Atmel® ATtiny87/167 and will always read as zero.

• Bits 3:0 – CLKPS3:0: Clock Prescaler Select Bits 3 - 0

These bits define the division factor between the selected clock source and the internal system clock. These bits can be

written run-time to vary the clock frequency to suit the application requirements. As the divider divides the master clock input

to the MCU, the speed of all synchronous peripherals is reduced when a division factor is used. The division factors are

given in Table 4-10.

To avoid unintentional changes of clock frequency, a special write procedure must be followed to change the CLKPS bits:

1. Write the Clock Prescaler Change Enable (CLKPCE) bit to one and all other bits in CLKPR to zero.

2. Within four cycles, write the desired value to CLKPS while writing a zero to CLKPCE.

Interrupts must be disabled when changing prescaler setting in order not to disturb the procedure.

The CKDIV8 fuse determines the initial value of the CLKPS bits. If CKDIV8 is unprogrammed, the CLKPS bits will be reset to

“0000”. If CKDIV8 is programmed, CLKPS bits are reset to “0011”, giving a division factor of eight at start up. This feature

should be used if the selected clock source has a higher frequency than the maximum frequency of the device at the present

operating conditions. Note that any value can be written to the CLKPS bits regardless of the CKDIV8 Fuse setting. The

application software must ensure that a sufficient division factor is chosen if the selected clock source has a higher

frequency than the maximum frequency of the device at the present operating conditions. The device is shipped with the

CKDIV8 fuse programmed.

Table 4-10. Clock Prescaler Select

CLKPS3 CLKPS2 CLKPS1 CLKPS0 Clock Division Factor

0 0 0 0 1

0 0 0 1 2

0 0 1 0 4

0 0 1 1 8

0 1 0 0 16

0 1 0 1 32

0 1 1 0 64

0 1 1 1 128

1 0 0 0 256

1 0 0 1 Reserved

1 0 1 0 Reserved

1 0 1 1 Reserved

1 1 0 0 Reserved

1 1 0 1 Reserved

1 1 1 0 Reserved

1 1 1 1 Reserved

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4.5.3 CLKCSR – Clock Control & Status Register

• Bit 7 – CLKCCE: Clock Control Change Enable

The CLKCCE bit must be written to logic one to enable change of the CLKCSR bits. The CLKCCE bit is only updated when

the other bits in CLKCSR are simultaneously written to zero. CLKCCE is cleared by hardware four cycles after it is written or

when the CLKCSR bits are written. Rewriting the CLKCCE bit within this time-out period does neither extend the time-out

period, nor clear the CLKCCE bit.

• Bits 6:5 – Res: Reserved Bits

These bits are reserved bits in the Atmel® ATtiny87/167 and will always read as zero.

• Bits 4 – CLKRDY: Clock Ready Flag

This flag is the output of the ‘clock availability ’ logic.

This flag is cleared by the ‘request for clock availability’ command or ‘enable clock source’ command being entered.

It is set when ‘clock availability’ logic confirms that the (selected) clock is running and is stable. The delay from the request

and the flag setting is not fixed, it depends on the clock start-up time, the clock frequency and, of course, if the clock is alive.

The user’s code has to differentiate between ‘no_clock_signal’ and ‘clock_signal_not_yet_available’ condition.

• Bits 3:0 – CLKC3:0: Clock Control Bits 3 - 0

These bits define the command to provide to the ‘Clock Switch’ module. The special write procedure must be followed to

change the CLKC3..0 bits (See ”Bit 7 – CLKCCE: Clock Control Change Enable” on page 40.).

1. Write the clock control change enable (CLKCCE) bit to one and all other bits in

CLKCSR to zero.

2. Within 4 cycles, write the desired value to CLKCSR register while clearing CLKCCE bit.

Interrupts should be disabled when setting CLKCSR register in order not to disturb the procedure.

Bit 7 65 4 3210

CLKCCE – – CLKRDY CLKC3 CLKC2 CLKC1 CLKC0 CLKCSR

Read/Write R/W R R R R/W R/W R/W R/W

Initial Value 0 0 0 0 0 0 0 0

Table 4-11. Clock Command List

Clock Command CLKC3..0

No command 0000 b

Disable clock source 0001 b

Enable clock source 0010 b

Request for clock availability 0011 b

Clock source switch 0100 b

Recover system clock source code 0101 b

Enable watchdog in automatic reload mode 0110 b

CKOUT command 0111 b

No command 1

xxx

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4.5.4 CLKSELR - Clock Selection Register

• Bit 7– Res: Reserved Bit

This bit is reserved bit in the Atmel® ATtiny87/167 and will always read as zero.

• Bit 6 – COUT: Clock Out

The COUT bit is initialized with ~(CKOUT) fuse bit.

The COUT bit is only used in case of ‘CKOUT’ command. Refer to Section 4.2.7 “Clock Output Buffer” on page 32 for using.

In case of ‘recover system clock Source’ command, COUT it is not affected (no recovering of this setting).

• Bits 5:4 – CSUT1:0: Clock Start-up Time

CSUT bits are initialized with the values of SUT fuse bits.

In case of ‘enable/disable clock source’ command, CSUT field provides the code of the clock start-up time. Refer to

subdivisions of Section 4.2 “Clock Sources” on page 26 for code of clock start-up times.

In case of ‘recover system clock source’ command, CSUT field is not affected (no recovering of SUT code).

• Bits 3:0 – CSEL3:0: Clock Source Select

CSEL bits are initialized with the values of CKSEL fuse bits.

In case of ‘enable/disable clock source’, ‘request for clock availability’ or ‘clock source switch’ command, CSEL field provides

the code of the clock source. Refer to Table 4-1 on page 26 and subdivisions of Section 4.2 “Clock Sources” on page 26 for

clock source codes.

In case of ‘recover system clock source’ command, CSEL field contains the code of the clock source used to drive the clock

control unit as described in Figure 4-1 on page 25.

Bit 7 6 543210

- COUT CSUT1 CSUT0 CSEL3 CSEL2 CSEL1 CSEL0 CLKSELR

Read/Write R R/W R/W R/W R/W R/W R/W R/W

Initial Value 0 ~ (CKOUT)

fuse

SUT1..0

fuses

CKSEL3..0

fuses

Note: 1. ForlNT1 anleTO, only \eve\ mlerrupl. AtmeL

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5. Power Management and Sleep Modes

Sleep modes enable the application to shut down unused modules in the MCU, thereby saving power. The AVR® provides

various sleep modes allowing the user to tailor the power consumption to the application’s requirements.

When enabled, the Brown-out Detector (BOD) actively monitors the power supply voltage during the sleep periods. To

further save power, it is possible to disable the BOD in some sleep modes. See Section 5.2 “BOD Disable” on page 42 for

more details.

5.1 Sleep Modes

Figure 4-1 on page 25 presents the different clock systems in the Atmel® ATtiny87/167, and their distribution. The figure is

helpful in selecting an appropriate sleep mode. Table 5-1 shows the different sleep modes, their wake up sources and BOD

disable ability.

To enter any of the four sleep modes, the SE bit in SMCR must be written to logic one and a SLEEP instruction must be

executed. The SM1, and SM0 bits in the SMCR register select which sleep mode (Idle, ADC noise reduction, power-down,

or power-save) will be activated by the SLEEP instruction. See Table 5-2 on page 45 for a summary.

If an enabled interrupt occurs while the MCU is in a sleep mode, the MCU wakes up. The MCU is then halted for four cycles

in addition to the start-up time, executes the interrupt routine, and resumes execution from the instruction following SLEEP.

The contents of the Register File and SRAM are unaltered when the device wakes up from sleep. If a reset occurs during

sleep mode, the MCU wakes up and executes from the reset vector.

5.2 BOD Disable

When the brown-out detector (BOD) is enabled by BODLEVEL fuses, Table 21-3 on page 208, the BOD is actively

monitoring the power supply voltage during a sleep period. To save power, it is possible to disable the BOD by software for

some of the sleep modes, see Table 5-1. The sleep mode power consumption will then be at the same level as when BOD is

globally disabled by fuses. If BOD is disabled in software, the BOD function is turned off immediately after entering the sleep

mode. Upon wake-up from sleep, BOD is automatically enabled again. This ensures safe operation in case the Vcc level has

dropped during the sleep period.

When the BOD has been disabled, the wake-up time from sleep mode will be approximately 60 µs to ensure that the BOD is

working correctly before the MCU continues executing code.

BOD disable is controlled by BODS bit (BOD Sleep) in the control register MCUCR, see Section 5.9.2 “MCUCR – MCU

Control Register” on page 45. Setting it to one turns off the BOD in relevant sleep modes, while a zero in this bit keeps BOD

active. Default setting keeps BOD active, i.e. BODS is cleared to zero.

Writing to the BODS bit is controlled by a timed sequence and an enable bit, see Section 5.9.2 “MCUCR – MCU Control

Table 5-1. Active Clock Domains and Wake-up Sources in the Different Sleep Modes

Active Clock Domains Oscillators Wake-up Sources

Software

BOD Disable

Sleep Mode

clkCPU

clkFLASH

clkIO

clkADC

clkASY

Main Clock

Source Enabled

Timer0 Osc.

Enable

INT1, INT0 and

Pin Change

SPM/EEPROM

Ready

ADC

WDT

USI Start Condition

Timer0

Other I/O

Idle X X X X X X X X X X X X

ADC Noise

Reduction X X X X X(1) X XXXX

Power-down X(1) X X X

Power-Save X X X(1) X X X X

Note: 1. For INT1 and INT0, only level interrupt.

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5.3 Idle Mode

When the SM1..0 bits are written to 00, the SLEEP instruction makes the MCU enter idle mode, stopping the CPU but

allowing the SPI, analog comparator, ADC, USI start condition, asynchronous timer/counter, watchdog, and the interrupt

system to continue operating. This sleep mode basically halts clkCPU and clkFLASH, while allowing the other clocks to run.

Idle mode enables the MCU to wake up from external triggered interrupts as well as internal ones like the SPI interrupts. If

wake-up from the analog comparator interrupt is not required, the analog comparator can be powered down by setting the

ACD bit in the analog comparator control and status register – ACSR. This will reduce power consumption in idle mode. If

the ADC is enabled, a conversion starts automatically when this mode is entered.

5.4 ADC Noise Reduction Mode

When the SM1..0 bits are written to 01, the SLEEP instruction makes the MCU enter ADC noise reduction mode, stopping

the CPU but allowing the ADC, the external interrupts, the USI start condition, the asynchronous timer/counter and the

watchdog to continue operating (if enabled). This sleep mode basically halts clkI/O, clkCPU, and clkFLASH, while allowing the

other clocks to run.

This improves the noise environment for the ADC, enabling higher resolution measurements. If the ADC is enabled, a

conversion starts automatically when this mode is entered. Apart from the ADC Conversion Complete interrupt, only an

external Reset, a watchdog system reset, a watchdog interrupt, a brown-out reset, a USI start condition interrupt, an

asynchronous timer/counter interrupt, an SPM/EEPROM ready interrupt, an external level interrupt on INT0 or INT1 or a pin

change interrupt can wake up the MCU from ADC noise reduction mode.

5.5 Power-down Mode

When the SM1..0 bits are written to 10, the SLEEP instruction makes the MCU enter power-down mode. In this mode, the

external oscillator is stopped, while the external interrupts, the USI start condition, and the watchdog continue operating (if

enabled). Only an external reset, a watchdog system reset, a watchdog interrupt, a brown-out reset, the USI start condition

interrupt, an external level interrupt on INT0 or INT1, or a pin change interrupt can wake up the MCU. This sleep mode

basically halts all generated clocks, allowing operation of asynchronous modules only.

Note that if a level triggered interrupt is used for wake-up from power-down mode, the changed level must be held for some

time to wake up the MCU. Refer to Section 8. “External Interrupts” on page 60 for details.

When waking up from power-down mode, there is a delay from the wake-up condition occurs until the wake-up becomes

effective. This allows the clock to restart and become stable after having been stopped. The wake-up period is defined by the

same CKSEL fuses that define the reset time-out period, as described in Section 4.2 “Clock Sources” on page 26.

5.6 Power-save Mode

When the SM1..0 bits are written to 11, the SLEEP instruction makes the MCU enter power-save mode. This mode is

identical to power-down, with one exception:

If timer/counter0 is clocked asynchronously, i.e., the AS0 bit in ASSR is set, timer/Counter0 will run during sleep. The device

can wake up from either Timer Overflow or Output Compare event from timer/counter0 if the corresponding timer/counter0

interrupt enable bits are set in TIMSK0, and the global interrupt enable bit in SREG is set.

If the asynchronous timer is NOT clocked asynchronously, power-down mode is recommended instead of power-save mode

because the contents of the registers in the asynchronous timer should be considered undefined after wake-up in power-

save mode if AS0 is 0.

This sleep mode basically halts all clocks except clkASY, allowing operation only of asynchronous modules, including

timer/counter0 if clocked asynchronously.

5.7 Power Reduction Register

The power reduction register (PRR), see Section 5.9.3 “PRR – Power Reduction Register” on page 46, provides a method to

stop the clock to individual peripherals to reduce power consumption. The current state of the peripheral is frozen and the I/O

registers can not be read or written. Resources used by the peripheral when stopping the clock will remain occupied, hence

the peripheral should in most cases be disabled before stopping the clock. Waking up a module, which is done by clearing

the bit in PRR, puts the module in the same state as before shutdown.

Module shutdown can be used in idle mode and Active mode to significantly reduce the overall power consumption. In all

other sleep modes, the clock is already stopped.

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5.8 Minimizing Power Consumption

There are several possibilities to consider when trying to minimize the power consumption in an AVR® controlled system. In

general, sleep modes should be used as much as possible, and the sleep mode should be selected so that as few as

possible of the device’s functions are operating. All functions not needed should be disabled. In particular, the following

modules may need special consideration when trying to achieve the lowest possible power consumption.

5.8.1 Analog to Digital Converter

If enabled, the ADC will be enabled in all sleep modes. To save power, the ADC should be disabled before entering any

sleep mode. When the ADC is turned off and on again, the next conversion will be an extended conversion. Refer to Section

17. “ADC – Analog to Digital Converter” on page 176 for details on ADC operation.

5.8.2 Analog Comparator

When entering idle mode, the analog comparator should be disabled if not used. When entering ADC noise reduction mode,

the analog comparator should be disabled. In other sleep modes, the analog comparator is automatically disabled. However,

if the analog comparator is set up to use the internal voltage reference as input, the analog comparator should be disabled in

all sleep modes. Otherwise, the Internal Voltage Reference will be enabled, independent of sleep mode. Refer to Section 18.

“AnaComp - Analog Comparator” on page 194 for details on how to configure the Analog Comparator.

5.8.3 Brown-out Detector

If the brown-out detector is not needed by the application, this module should be turned off. If the brown-out detector is

enabled by the BODLEVEL fuses, it will be enabled in all sleep modes, and hence, always consume power. In the deeper

sleep modes, this will contribute significantly to the total current consumption. Refer to Section 6.1.5 “Brown-out Detection”

on page 49 for details on how to configure the brown-out detector.

5.8.4 Internal Voltage Reference

The internal voltage reference will be enabled when needed by the brown-out detection, the analog comparator or the ADC.

If these modules are disabled as described in the sections above, the internal voltage reference will be disabled and it will

not be consuming power. When turned on again, the user must allow the reference to start up before the output is used. If

the reference is kept on in sleep mode, the output can be used immediately. Refer to Section 6.2 “Internal Voltage

Reference” on page 51 for details on the start-up time.

Output the internal voltage reference is not needed in the deeper sleep modes. This module should be turned off to reduce

significantly to the total current consumption. Refer to Section 16.3.1 “AMISCR – Analog Miscellaneous Control Register” on

page 175 for details on how to disable the internal voltage reference output.

5.8.5 Internal Current Source

The internal current source is not needed in the deeper sleep modes. This module should be turned off to reduce

significantly to the total current consumption. Refer to Section 16.3.1 “AMISCR – Analog Miscellaneous Control Register” on

page 175 for details on how to disable the internal current source.

5.8.6 Watchdog Timer

If the watchdog timer is not needed in the application, the module should be turned off. If the watchdog timer is enabled, it

will be enabled in all sleep modes and hence always consume power. In the deeper sleep modes, this will contribute

significantly to the total current consumption. Refer to Section 6.3 “Watchdog Timer” on page 51 for details on how to

configure the watchdog timer.

5.8.7 Port Pins

When entering a sleep mode, all port pins should be configured to use minimum power. The most important is then to ensure

that no pins drive resistive loads. In sleep modes where both the I/O clock (clkI/O) and the ADC clock (clkADC) are stopped,

the input buffers of the device will be disabled. This ensures that no power is consumed by the input logic when not needed.

In some cases, the input logic is needed for detecting wake-up conditions, and it will then be enabled. Refer to the section

Section 9.2.6 “Digital Input Enable and Sleep Modes” on page 69 for details on which pins are enabled. If the input buffer is

enabled and the input signal is left floating or have an analog signal level close to Vcc/2, the input buffer will use excessive

power.

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For analog input pins, the digital input buffer should be disabled at all times. An analog signal level close to Vcc/2 on an input

pin can cause significant current even in active mode. Digital input buffers can be disabled by writing to the digital input

disable registers (DIDR1 and DIDR0). Refer to Section 17.11.6 “DIDR1 – Digital Input Disable Register 1” on page 192 and

Section 17.11.5 “DIDR0 – Digital Input Disable Register 0” on page 192 for details.

5.8.8 On-chip Debug System

If the on-chip debug system is enabled by the DWEN fuse and the chip enters sleep mode, the main clock source is enabled

and hence always consumes power. In the deeper sleep modes, this will contribute significantly to the total current

consumption.

5.9 Register Description

5.9.1 SMCR – Sleep Mode Control Register

The sleep mode control register contains control bits for power management.

• Bits 7..3 Res: Reserved Bits

These bits are unused bits in the Atmel® ATtiny87/167, and will always read as zero.

• Bits 2..1 – SM1..0: Sleep Mode Select Bits 1, and 0

These bits select between the four available sleep modes as shown in Table 5-2.

• Bit 0 – SE: Sleep Enable

The SE bit must be written to logic one to make the MCU enter the sleep mode when the SLEEP instruction is executed. To

avoid the MCU entering the sleep mode unless it is the programmer’s purpose, it is recommended to write the sleep enable

(SE) bit to one just before the execution of the SLEEP instruction and to clear it immediately after waking up.

5.9.2 MCUCR – MCU Control Register

• Bit 6 – BODS: BOD Sleep

The BODS bit must be written to logic one in order to turn off BOD during sleep, see Table 5-1 on page 42. Writing to the

BODS bit is controlled by a timed sequence and an enable bit, BODSE in MCUCR. To disable BOD in relevant sleep modes,

both BODS and BODSE must first be set to one. Then, to set the BODS bit, BODS must be set to one and BODSE must be

set to zero within four clock cycles.

The BODS bit is active three clock cycles after it is set. A sleep instruction must be executed while BODS is active in order to

turn off the BOD for the actual sleep mode. The BODS bit is automatically cleared after three clock cycles.

Bit 76543210

–––––SM1SM0SESMCR

Read/Write RRRRRR/WR/WR/W

Initial Value00000000

Table 5-2. Sleep Mode Select

SM1 SM0 Sleep Mode

0 0 Idle

0 1 ADC noise reduction

1 0 Power-down

1 1 Power-save

Bit 7 6 5 4 3 2 1 0

–BODS BODSE PUD – – – – MCUCR

Read/Write R R/W R/W R/W R R R R

Initial Value 0 0 0 0 0 0 0 0

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• Bit 5 – BODSE: BOD Sleep Enable

BODSE enables setting of BODS control bit, as explained in BODS bit description. BOD disable is controlled by a timed

sequence.

5.9.3 PRR – Power Reduction Register

• Bit 7 - Res: Reserved bit

This bit is reserved in Atmel® ATtiny87/167 and will always read as zero.

• Bit 6 - Res: Reserved bit

This bit is reserved in Atmel ATtiny87/167 and will always read as zero.

• Bit5 - PRLIN: Power Reduction LIN / UART controller

Writing a logic one to this bit shuts down the LIN by stopping the clock to the module. When waking up the LIN again, the LIN

should be re initialized to ensure proper operation.

• Bit 4 - PRSPI: Power Reduction Serial Peripheral Interface

If using debugWIRE on-chip debug system, this bit should not be written to one.

Writing a logic one to this bit shuts down the serial peripheral interface by stopping the clock to the module. When waking up

the SPI again, the SPI should be re initialized to ensure proper operation.

• Bit 3 - PRTIM1: Power Reduction Timer/Counter1

Writing a logic one to this bit shuts down the timer/counter1 module. When the timer/counter1 is enabled, operation will

continue like before the shutdown.

• Bit 2 - PRTIM0: Power Reduction Timer/Counter0

Writing a logic one to this bit shuts down the timer/counter0 module in synchronous mode (AS0 is 0). When the

timer/counter0 is enabled, operation will continue like before the shutdown.

• Bit 1 - PRUSI: Power Reduction USI

Writing a logic one to this bit shuts down the USI by stopping the clock to the module. When waking up the USI again, the

USI should be re-initialized to ensure proper operation.

• Bit 0 - PRADC: Power Reduction ADC

Writing a logic one to this bit shuts down the ADC. The ADC must be disabled before shut down. The analog comparator

cannot use the ADC input MUX when the ADC is shut down.

Bit 76543210

– – PRLIN PRSPI PRTIM1 PRTIM0 PRUSI PRADC PRR

Read/Write R R R/W R/W R/W R/W R/W R/W

Initial Value00000000

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6. System Control and Reset

6.1 Reset

6.1.1 Resetting the AVR

During reset, all I/O registers are set to their initial values, and the program starts execution from the reset vector. The

instruction placed at the reset vector must be an RJMP – Relative Jump – instruction to the reset handling routine. If the

program never enables an interrupt source, the interrupt vectors are not used, and regular program code can be placed at

these locations. The circuit diagram in Figure 6-1 shows the reset circuit. Tables in Section 22.5 “RESET Characteristics” on

page 225 defines the electrical parameters of the reset circuitry.

The I/O ports of the AVR® are immediately reset to their initial state when a reset source goes active. This does not require

any clock source to be running.

After all reset sources have gone inactive, a delay counter is invoked, stretching the internal reset. This allows the power to

reach a stable level before normal operation starts. The time-out period of the delay counter is defined by the user through

the SUT and CKSEL fuses. The different selections for the delay period are presented in Section 4.2 “Clock Sources” on

page 26.

6.1.2 Reset Sources

The Atmel® ATtiny87/167 has four sources of reset:

●Power-on reset. The MCU is reset when the supply voltage is below the power-on reset threshold (VPOT).

●External reset. The MCU is reset when a low level is present on the RESET pin for longer than the minimum pulse

length.

●Watchdog system reset. The MCU is reset when the watchdog timer period expires and the watchdog system reset

mode is enabled.

●Brown-out reset. The MCU is reset when the supply voltage Vcc is below the brown-out reset threshold (VBOT) and the

brown-out detector is enabled.

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Figure 6-1. Reset Circuit

6.1.3 Power-on Reset

A power-on reset (POR) pulse is generated by an on-chip detection circuit. The detection level is defined in Table 22-4 on

page 225. The POR is activated whenever Vcc is below the detection level. The POR circuit can be used to trigger the start-

up reset, as well as to detect a failure in supply voltage.

A power-on reset (POR) circuit ensures that the device is reset from power-on. Reaching the power-on reset threshold

voltage invokes the delay counter, which determines how long the device is kept in RESET after Vcc rise. The RESET signal

is activated again, without any delay, when Vcc decreases below the detection level.

Figure 6-2. MCU Start-up, RESET Tied to Vcc

Power-on Reset

Circuit

Brown-out

Reset Circuit

MCU Status

Reset Circuit

Pull-up Resistor

BODLEVEL[2..0]

DATA BUS

SUT[1:0]

CKSEL[3:0]

RSTDISBL

COUNTER RESET

INTERNAL RESET

TIME-OUT

Spike

Filter

RESET

VCC

Delay Counters

Watchdog

Timer

Watchdog

Oscillator

Clock

Generator

PORF

BORF

WDRF

EXTRF

VCC

INTERNAL

RESET

TIME-OUT

tTOUT

VPORMAX

VPORMIN

VPOT

VCCRR

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Figure 6-3. MCU Start-up, RESET Extended Externally

6.1.4 External Reset

An external reset is generated by a low level on the RESET pin. Reset pulses longer than the minimum pulse width (see

Table 22-3 on page 225) will generate a reset, even if the clock is not running. Shorter pulses are not guaranteed to generate

a reset. When the applied signal reaches the reset threshold voltage – VRST – on its positive edge, the delay counter starts

the MCU after the time-out period – tTOUT – has expired. The external reset can be disabled by the RSTDISBL fuse, see

Table 21-4 on page 208.

Figure 6-4. External Reset During Operation

6.1.5 Brown-out Detection

Atmel® ATtiny87/167 has an on-chip brown-out detection (BOD) circuit for monitoring the Vcc level during operation by

comparing it to a fixed trigger level. The trigger level for the BOD can be selected by the BODLEVEL fuses (Section 22-5

“BODLEVEL Fuse Coding” on page 226). The trigger level has a hysteresis to ensure spike free Brown-out Detection. The

hysteresis on the detection level should be interpreted as VBOT+ = VBOT + VHYST / 2 and VBOT– = VBOT - VHYST / 2.

VCC

INTERNAL

RESET

TIME-OUT

POR

RST

TOUT

VCCRR

tTOUT

RESET

VCC

INTERNAL

RESET

TIME-OUT

VRST

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When the BOD is enabled, and Vcc decreases to a value below the trigger level (VBOT– in Figure 6-5), the brown-out reset is

immediately activated. When Vcc increases above the trigger level (VBOT+ in Figure 6-5), the delay counter starts the MCU

after the time-out period tTOUT has expired.

The BOD circuit will only detect a drop in Vcc if the voltage stays below the trigger level for longer than tBOD given in Tabl e

22-6 on page 226.

Figure 6-5. Brown-out Reset During Operation

6.1.6 Watchdog System Reset

When the watchdog times out, it will generate a short reset pulse of one CK cycle duration. On the falling edge of this pulse,

the delay timer starts counting the time-out period tTOUT. Refer to page 51 for details on operation of the watchdog timer.

Figure 6-6. Watchdog System Reset During Operation

6.1.7 MCU Status Register – MCUSR

The MCU status register provides information on which reset source caused an MCU reset.

• Bit 7..4 – Res: Reserved Bits

These bits are unused bits in the Atmel® ATtiny87/167, and will always read as zero.

• Bit 3 – WDRF: Watchdog System Reset Flag

This bit is set if a watchdog system reset occurs. The bit is reset by a power-on reset, or by writing a logic zero to the flag.

VBOT-

VBOT+

tTOUT

VCC

RESET

INTERNAL

RESET

TIME-OUT

1 CK Cycle

VCC

RESET

INTERNAL

RESET

Time-OUT

TIME-OUT

tTOUT

Bit 76543210

––––WDRFBORFEXTRFPORFMCUSR

Read/Write RRRRR/WR/WR/WR/W

Initial Value0000 See Bit Description

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• Bit 2 – BORF: Brown-out Reset Flag

This bit is set if a brown-out reset occurs. The bit is reset by a power-on reset, or by writing a logic zero to the flag.

• Bit 1 – EXTRF: External Reset Flag

This bit is set if an external reset occurs. The bit is reset by a power-on reset, or by writing a logic zero to the flag.

• Bit 0 – PORF: Power-on Reset Flag

This bit is set if a power-on reset occurs. The bit is reset only by writing a logic zero to the flag.

To make use of the reset flags to identify a reset condition, the user should read and then reset the MCUSR as early as

possible in the program. If the register is cleared before another reset occurs, the source of the reset can be found by

examining the reset flags.

6.2 Internal Voltage Reference

Atmel® ATtiny87/167 features an internal bandgap reference. This reference is used for brown-out detection, and it can be

used as an input to the analog comparator or the ADC.

6.2.1 Voltage Reference Enable Signals and Start-up Time

The voltage reference has a start-up time that may influence the way it should be used. The start-up time is given in Table

22-7 on page 226. To save power, the reference is not always turned on. The reference is on during the following situations:

1. When the BOD is enabled (by programming the BODLEVEL [2:0] fuses).

2. When the bandgap reference is connected to the analog comparator (by setting the ACIRS bit in ACSR).

3. When the ADC is enabled.

Thus, when the BOD is not enabled, after setting the ACIRS bit or enabling the ADC, the user must always allow the

reference to start up before the output from the analog comparator or ADC is used. To reduce power consumption in power-

down mode or in power-save, the user can avoid the three conditions above to ensure that the reference is turned off before

entering in these power reduction modes.

6.3 Watchdog Timer

Atmel ATtiny87/167 has an enhanced watchdog timer (WDT). The main features are:

●Clocked from separate on-chip oscillator

●4 Operating modes

●Interrupt

●System Reset

●Interrupt and System Reset

●Clock Monitoring

●Selectable time-out period from 16ms to 8s

●Possible hardware fuse watchdog always on (WDTON) for fail-safe mode

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6.3.1 Watchdog Timer Behavior

The watchdog timer (WDT) is a timer counting cycles of a separate on-chip 128KHz oscillator.

Figure 6-7. Watchdog Timer

The WDT gives an interrupt or a system reset when the counter reaches a given time-out value. In normal operation mode, it

is required that the system uses the WDR - watchdog timer reset - instruction to restart the counter before the time-out value

is reached. If the system doesn't restart the counter, an interrupt or system reset will be issued.

In interrupt mode, the WDT gives an interrupt when the timer expires. This interrupt can be used to wake the device from

sleep-modes, and also as a general system timer. One example is to limit the maximum time allowed for certain operations,

giving an interrupt when the operation has run longer than expected. In system reset mode, the WDT gives a reset when the

timer expires. This is typically used to prevent system hang-up in case of runaway code. The third mode, interrupt and

system reset mode, combines the other two modes by first giving an interrupt and then switch to system reset mode. This

mode will for instance allow a safe shutdown by saving critical parameters before a system reset.

The watchdog always on (WDTON) fuse, if programmed, will force the watchdog timer to system reset mode. With the fuse

programmed the system reset mode bit (WDE) and interrupt mode bit (WDIE) are locked to 1 and 0 respectively. To further

ensure program security, alterations to the watchdog set-up must follow timed sequences. The sequence for clearing WDE

and changing time-out configuration is as follows:

1. In the same operation, write a logic one to the watchdog change enable bit (WDCE) and WDE. A logic one must

be written to WDE regardless of the previous value of the WDE bit.

2. Within the next four clock cycles, write the WDE and watchdog prescaler bits (WDP) as desired, but with the

WDCE bit cleared. This must be done in one operation.

OSC/64K

OSC/16K

OSC/2K

OSC/4K

OSC/8K

OSC/32K

OSC/128K

OSC/256K

OSC/512K

OSC/1024K

Watchdog

Prescaler

WDP0

WDE

WATCHDOG

RESET

CLOCK

MONITORING

WDIF

WDIE

WDP1

WDP2

WDP3

MCU RESET

INTERRUPT

~128kHz

Oscillator

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The following code example shows one assembly and one C function for turning off the watchdog timer. The example

assumes that interrupts are controlled (e.g. by disabling interrupts globally) so that no interrupts will occur during the

execution of these functions.

Note: 1. See Section 1.9 “About Code Examples” on page 7.

Note that if the watchdog is accidentally enabled, for example by a runaway pointer or brown-out condition, the device will be

reset and the watchdog timer will stay enabled. If the code is not set up to handle the watchdog, this might lead to an eternal

loop of time-out resets. To avoid this situation, the application software should always clear the watchdog system reset flag

(WDRF) and the WDE control bit in the initialization routine, even if the watchdog is not in use.

Assembly Code Example(1)

WDT_off:

; Turn off global interrupt

cli

; Reset Watchdog Timer

wdr

; Clear WDRF in MCUSR

in r16, MCUSR

andi r16, (0xff & (0<<WDRF))

out MCUSR, r16

; Write logical one to WDCE and WDE

; Keep old prescaler setting to prevent unintentional time-out

lds r16, WDTCR

ori r16, (1<<WDCE) | (1<<WDE)

sts WDTCR, r16

; Turn off WDT

ldi r16, (0<<WDE)

sts WDTCR, r16

; Turn on global interrupt

sei

ret

C Code Example(1)

void WDT_off(void)

{

__disable_interrupt();

__watchdog_reset();

/* Clear WDRF in MCUSR */

MCUSR &= ~(1<<WDRF);

/* Write logical one to WDCE and WDE */

/* Keep old prescaler setting to prevent unintentional time-out */

WDTCR |= (1<<WDCE) | (1<<WDE);

/* Turn off WDT */

WDTCR = 0x00;

__enable_interrupt();

}

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The following code example shows one assembly and one C function for changing the time-out value of the watchdog timer.

Notes: 1. See Section 1.9 “About Code Examples” on page 7.

2. The watchdog timer should be reset before any change of the WDP bits, since a change in the WDP bits can

result in a time-out when switching to a shorter time-out period.

6.3.2 Clock monitoring

The watchdog timer can be used to detect a loss of system clock. This configuration is driven by the dynamic clock switch

circuit. Please refer to Section 4.3.8 “Clock Monitoring” on page 36 for more information.

Assembly Code Example(1)

WDT_Prescaler_Change:

; Turn off global interrupt

cli

; Reset Watchdog Timer

wdr

; Start timed sequence

lds r16, WDTCR

ori r16, (1<<WDCE) | (1<<WDE)

sts WDTCR, r16

; -- Got four cycles to set the new values from here -

; Set new prescaler(time-out) value = 64K cycles (~0.5 s)

ldi r16, (1<<WDE) | (1<<WDP2) | (1<<WDP0)

sts WDTCR, r16

; -- Finished setting new values, used 2 cycles -

; Turn on global interrupt

sei

ret

C Code Example(1)

void WDT_Prescaler_Change(void)

{

__disable_interrupt();

__watchdog_reset();

/* Start timed sequence */

WDTCR |= (1<<WDCE) | (1<<WDE);

/* Set new prescaler(time-out) value = 64K cycles (~0.5 s) */

WDTCR = (1<<WDE) | (1<<WDP2) | (1<<WDP0);

__enable_interrupt();

}

Note: 1. At lees: one of khese three enables (WDTON, WDE & WDIE) equal to 1. AtmeL

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6.3.3 Watchdog Timer Control Register - WDTCR

• Bit 7 - WDIF: Watchdog Interrupt Flag

This bit is set when a time-out occurs in the watchdog timer and the watchdog timer is configured for interrupt. WDIF is

cleared by hardware when executing the corresponding interrupt handling vector. Alternatively, WDIF is cleared by writing a

logic one to the flag. When the I-bit in SREG and WDIE are set, the watchdog time-out interrupt is executed.

• Bit 6 - WDIE: Watchdog Interrupt Enable

When this bit is written to one and the I-bit in the status register is set, the watchdog interrupt is enabled. If WDE is cleared in

combination with this setting, the watchdog timer is in interrupt mode, and the corresponding interrupt is executed if time-out

in the watchdog timer occurs.

If WDE is set, the watchdog timer is in interrupt and system reset mode. The first time-out in the watchdog timer will set

WDIF. Executing the corresponding interrupt vector will clear WDIE and WDIF automatically by hardware (the watchdog

goes to system reset mode). This is useful for keeping the watchdog timer security while using the interrupt. To stay in

interrupt and system reset mode, WDIE must be set after each interrupt. This should however not be done within the

interrupt service routine itself, as this might compromise the safety-function of the watchdog system reset mode. If the

interrupt is not executed before the next time-out, a system reset will be applied.

If the watchdog timer is used as clock monitor (c.f. Section • “Bits 3:0 – CLKC3:0: Clock Control Bits 3 - 0” on page 40), the

system reset mode is enabled and the interrupt mode is automatically disabled.

• Bit 4 - WDCE: Watchdog Change Enable

This bit is used in timed sequences for changing WDE and prescaler bits. To clear the WDE bit, and/or change the prescaler

bits, WDCE must be set.

Once written to one, hardware will clear WDCE after four clock cycles.

• Bit 3 - WDE: Watchdog System Reset Enable

WDE is overridden by WDRF in MCUSR. This means that WDE is always set when WDRF is set. To clear WDE, WDRF

must be cleared first. This feature ensures multiple resets during conditions causing failure, and a safe start-up after the

failure.

• Bit 5, 2..0 - WDP3..0: Watchdog Timer Prescaler 3, 2, 1 and 0

The WDP3..0 bits determine the watchdog timer prescaling when the watchdog timer is running. The different prescaling

values and their corresponding time-out periods are shown in Table 6-2 on page 56.

Bit 76543210

WDIF WDIE WDP3 WDCE WDE WDP2 WDP1 WDP0 WDTCR

Read/Write R/W R/W R/W R/W R/W R/W R/W R/W

Initial Value 0 0 0 0 X 0 0 0

Table 6-1. Watchdog Timer Configuration

Clock

Monitor WDTON WDE WDIE Mode Action on Time-out

x 0 0 0 Stopped None

On y(1) y(1) y(1) System Reset Mode Reset

Off

0 0 1 Interrupt Mode Interrupt

0 1 0 System Reset Mode Reset

0 1 1 Interrupt and System Reset Mode Interrupt, then go to System Reset

Mode

1 x x System Reset Mode Reset

Note: 1. At least one of these three enables (WDTON, WDE & WDIE) equal to 1.

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Table 6-2. Watchdog Timer Prescale Select

WDP3 WDP2 WDP1 WDP0

Number of

WDT Oscillator Cycles

Typical Time-out

at Vcc = 5.0V

0 0 0 0 2K(2048)cycles 16ms

0 0 0 1 4K(4096) ycles 32ms

0 0 1 0 8K(8192)cycles 64ms

0 0 1 1 16K(16384)cycles 0.125s

0 1 0 0 32K(32768)cycles 0.25s

0 1 0 1 64K(65536)cycles 0.5s

0 1 1 0 128K(131072)cycles 1.0s

0 1 1 1 256K(262144)cycles 2.0s

1 0 0 0 512K(524288)cycles 4.0s

1 0 0 1 1024K(1048576)cycles 8.0s

1 0 1 0

Reserved

1 0 1 1

1 1 0 0

1 1 0 1

1 1 1 0

1 1 1 1

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7. Interrupts

This section describes the specifics of the interrupt handling as performed in Atmel® ATtiny87/167. For a general explanation

of the AVR® interrupt handling, refer to “Reset and Interrupt Handling” on page 13.

7.1 Interrupt Vectors in ATtiny87/167

Table 7-1. Reset and Interrupt Vectors in ATtiny87/167

Vector

Nb.

Program Address

Source Interrupt DefinitionATtiny87 ATtiny167

10x0000 0x0000 RESET External Pin, Power-on Reset, Brown-out Reset

and Watchdog System Reset

20x0001 0x0002 INT0 External Interrupt Request 0

30x0002 0x0004 INT1 External Interrupt Request 1

40x0003 0x0006 PCINT0 Pin Change Interrupt Request 0

50x0004 0x0008 PCINT1 Pin Change Interrupt Request 1

60x0005 0x000A WDT Watchdog Time-out Interrupt

70x0006 0x000C TIMER1 CAPT Timer/Counter1 Capture Event

80x0007 0x000E TIMER1 COMPA Timer/Counter1 Compare Match A

90x0008 0x0010 TIMER1 COMPB Timer/Coutner1 Compare Match B

10 0x0009 0x0012 TIMER1 OVF Timer/Counter1 Overflow

11 0x000A 0x0014 TIMER0 COMPA Timer/Counter0 Compare Match A

12 0x000B 0x0016 TIMER0 OVF Timer/Counter0 Overflow

13 0x000C 0x0018 LIN TC LIN/UART Transfer Complete

14 0x000D 0x001A LIN ERR LIN/UART Error

15 0x000E 0x001C SPI, STC SPI Serial Transfer Complete

16 0x000F 0x001E ADC ADC Conversion Complete

17 0x0010 0x0020 EE READY EEPROM Ready

18 0x0011 0x0022 ANALOG COMP Analog Comparator

19 0x0012 0x0024 USI START USI Start Condition Detection

20 0x0013 0x0026 USI OVF USI Counter Overflow

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7.2 Program Setup in ATtiny87

The most typical and general program setup for the reset and interrupt vector addresses in Atmel® ATtiny87 is (2-byte step -

using “rjmp” instruction):

Address(1)Label Code Comments

0x0000 rjmp RESET ; Reset Handler

0x0001 rjmp INT0addr ; IRQ0 Handler

0x0002 rjmp INT1addr ; IRQ1 Handler

0x0003 rjmp PCINT0addr ; PCINT0 Handler

0x0004 rjmp PCINT1addr ; PCINT1 Handler

0x0005 rjmp WDTaddr ; Watchdog Timer Handler

0x0006 rjmp ICP1addr ; Timer1 Capture Handler

0x0007 rjmp OC1Aaddr ; Timer1 Compare A Handler

0x0008 rjmp OC1Baddr ; Timer1 Compare B Handler

0x0009 rjmp OVF1addr ; Timer1 Overflow Handler

0x000A rjmp OC0Aaddr ; Timer0 Compare A Handler

0x000B rjmp OVF0addr ; Timer0 Overflow Handler

0x000C rjmp LINTCaddr ; LIN Transfer Complete Handler

0x000D rjmp LINERRaddr ; LIN Error Handler

0x000E rjmp SPIaddr ; SPI Transfer Complete Handler

0x000F rjmp ADCCaddr ; ADC Conversion Complete Handler

0x0010 rjmp ERDYaddr ; EEPROM Ready Handler

0x0011 rjmp ACIaddr ; Analog Comparator Handler

0x0012 rjmp USISTARTaddr ; USI Start Condition Handler

0x0013 rjmp USIOVFaddr ; USI Overflow Handler

0x0014 RESET: ldi r16, high(RAMEND); Main program start

0x0015 out SPH,r16 ; Set Stack Pointer to top of RAM

0x0016 ldi r16, low(RAMEND)

0x0017 out SPL,r16

0x0018 sei ; Enable interrupts

0x0019 <instr> xxx

... ... ... ...

Note: 1. 16-bit address

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7.3 Program Setup in ATtiny167

The most typical and general program setup for the reset and interrupt vector addresses in Atmel® ATtiny167 is (4-byte step

- using “jmp” instruction):

Address(1)Label Code Comments

0x0000 jmp RESET ; Reset Handler

0x0002 jmp INT0addr ; IRQ0 Handler

0x0004 jmp INT1addr ; IRQ1 Handler

0x0006 jmp PCINT0addr ; PCINT0 Handler

0x0008 jmp PCINT1addr ; PCINT1 Handler

0x000A jmp WDTaddr ; Watchdog Timer Handler

0x000C jmp ICP1addr ; Timer1 Capture Handler

0x000E jmp OC1Aaddr ; Timer1 Compare A Handler

0x0010 jmp OC1Baddr ; Timer1 Compare B Handler

0x0012 jmp OVF1addr ; Timer1 Overflow Handler

0x0014 jmp OC0Aaddr ; Timer0 Compare A Handler

0x0016 jmp OVF0addr ; Timer0 Overflow Handler

0x0018 jmp LINTCaddr ; LIN Transfer Complete Handler

0x001A jmp LINERRaddr ; LIN Error Handler

0x001C jmp SPIaddr ; SPI Transfer Complete Handler

0x001E jmp ADCCaddr ; ADC Conversion Complete Handler

0x0020 jmp ERDYaddr ; EEPROM Ready Handler

0x0022 jmp ACIaddr ; Analog Comparator Handler

0x0024 jmp USISTARTaddr ; USI Start Condition Handler

0x0026 jmp USIOVFaddr ; USI Overflow Handler

0x0028 RESET: ldi r16, high(RAMEND); Main program start

0x0029 out SPH,r16 ; Set Stack Pointer to top of RAM

0x002A ldi r16, low(RAMEND)

0x002B out SPL,r16

0x002C sei ; Enable interrupts

0x002D <instr> xxx

... ... ... ...

Note: 1. 16-bit address

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8. External Interrupts

8.1 Overview

The external interrupts are triggered by the INT1..0 pins or any of the PCINT15..0 pins. Observe that, if enabled, the

interrupts will trigger even if the INT1..0 or PCINT15..0 pins are configured as outputs. This feature provides a way of

generating a software interrupt.

The pin change interrupt PCINT1 will trigger if any enabled PCINT15..8 pin toggles. The pin change interrupt PCINT0 will

trigger if any enabled PCINT7..0 pin toggles. The PCMSK1 and PCMSK0 Registers control which pins contribute to the pin

change interrupts. Pin change interrupts on PCINT15..0 are detected asynchronously. This implies that these interrupts can

be used for waking the part also from sleep modes other than Idle mode.

The INT1..0 interrupts can be triggered by a falling or rising edge or a low level. This is set up as indicated in the specification

for the external interrupt control register A – EICRA. When the INT1..0 interrupts are enabled and are configured as level

triggered, the interrupts will trigger as long as the pin is held low. The recognition of falling or rising edge interrupts on

INT1..0 requires the presence of an I/O clock, described in Section 4.1 “Clock Systems and their Distribution” on page 25.

Low level interrupts and the edge interrupt on INT1..0 are detected asynchronously. This implies that these interrupts can be

used for waking the part also from sleep modes other than Idle mode. The I/O clock is halted in all sleep modes except idle

mode.

Note that if a level triggered interrupt is used for wake-up from power-down or power-save, the required level must be held

long enough for the MCU to complete the wake-up to trigger the level interrupt. If the level disappears before the end of the

Start-up Time, the MCU will still wake up, but no interrupt will be generated. The start-up time is defined by the SUT and

CKSEL Fuses as described in Section 4.1 “Clock Systems and their Distribution” on page 25.

8.2 Pin Change Interrupt Timing

An example of timing of a pin change interrupt is shown in Figure 8-1.

Figure 8-1. Timing of pin change interrupts

clk

pin_lat

pin_sync

PCINT[i] pin

pcint_in[i]

pcint_syn

pcint_set/flag

PCIFn

pin_lat pin_sync

pcint_sync

clk

pcint_set/flag

PCINT[I] bit

(of PCMSKn)

PCINT[I]

PCIFn

(interrupt flag)

pcint_in[i]

DQ DQ DQ DQ

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8.3 External Interrupts Register Description

8.3.1 External Interrupt Control Register A – EICRA

The external interrupt control register A contains control bits for interrupt sense control.

• Bit 7..4 – Res: Reserved Bits

These bits are unused bits in the Atmel® ATtiny87/167, and will always read as zero.

• Bit 3, 2 – ISC11, ISC10: Interrupt Sense Control 1 Bit 1 and Bit 0

The external interrupt 1 is activated by the external pin INT1 if the SREG I-flag and the corresponding interrupt mask are set.

The level and edges on the external INT1 pin that activate the interrupt are defined in Table 8-1. The value on the INT1 pin is

sampled before detecting edges. If edge or toggle interrupt is selected, pulses that last longer than one clock period will

generate an interrupt. Shorter pulses are not guaranteed to generate an interrupt. If low level interrupt is selected, the low

level must be held until the completion of the currently executing instruction to generate an interrupt.

• Bit 1, 0 – ISC01, ISC00: Interrupt Sense Control 0 Bit 1 and Bit 0

The external interrupt 0 is activated by the external pin INT0 if the SREG I-flag and the corresponding interrupt mask are set.

The level and edges on the external INT0 pin that activate the interrupt are defined in Table 8-1. The value on the INT0 pin is

sampled before detecting edges. If edge or toggle interrupt is selected, pulses that last longer than one clock period will

generate an interrupt. Shorter pulses are not guaranteed to generate an interrupt. If low level interrupt is selected, the low

level must be held until the completion of the currently executing instruction to generate an interrupt.

8.3.2 External Interrupt Mask Register – EIMSK

• Bit 7, 2 – Res: Reserved Bits

These bits are unused bits in the Atmel ATtiny87/167, and will always read as zero.

• Bit 1 – INT1: External Interrupt Request 1 Enable

When the INT1 bit is set (one) and the I-bit in the status register (SREG) is set (one), the external pin interrupt is enabled.

The interrupt sense control1 bits 1/0 (ISC11 and ISC10) in the external interrupt control register A (EICRA) define whether

the external interrupt is activated on rising and/or falling edge of the INT1 pin or level sensed. Activity on the pin will cause an

interrupt request even if INT1 is configured as an output. The corresponding interrupt of external interrupt request 1 is

executed from the INT1 interrupt vector.

Bit 76543210

––––ISC11ISC10ISC01ISC00EICRA

Read/Write RRRRR/WR/WR/WR/W

Initial Value00000000

Table 8-1. Interrupt Sense Control

ISCn1 ISCn0 Description

0 0 The low level of INTn generates an interrupt request.

0 1 Any logical change on INTn generates an interrupt request.

1 0 The falling edge of INTn generates an interrupt request.

1 1 The rising edge of INTn generates an interrupt request.

Bit 76543210

––––––INT1INT0EIMSK

Read/WriteRRRRRRR/WR/W

Initial Value00000000

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Bit 0 – INT0: External Interrupt Request 0 Enable

When the INT0 bit is set (one) and the I-bit in the status register (SREG) is set (one), the external pin interrupt is enabled.

The interrupt sense control0 bits 1/0 (ISC01 and ISC00) in the external interrupt control register A (EICRA) define whether

the external interrupt is activated on rising and/or falling edge of the INT0 pin or level sensed. Activity on the pin will cause an

interrupt request even if INT0 is configured as an output. The corresponding interrupt of external interrupt request 0 is

executed from the INT0 interrupt vector.

8.3.3 External Interrupt Flag Register – EIFR

• Bit 7, 2 – Res: Reserved Bits

These bits are unused bits in the Atmel® ATtiny87/167, and will always read as zero.

• Bit 1 – INTF1: External Interrupt Flag 1

When an edge or logic change on the INT1 pin triggers an interrupt request, INTF1 becomes set (one). If the I-bit in SREG

and the INT1 bit in EIMSK are set (one), the MCU will jump to the corresponding interrupt vector. The flag is cleared when

the interrupt routine is executed. Alternatively, the flag can be cleared by writing a logical one to it. This flag is always cleared

when INT1 is configured as a level interrupt.

• Bit 0 – INTF0: External Interrupt Flag 0

When an edge or logic change on the INT0 pin triggers an interrupt request, INTF0 becomes set (one). If the I-bit in SREG

and the INT0 bit in EIMSK are set (one), the MCU will jump to the corresponding interrupt vector. The flag is cleared when

the interrupt routine is executed. Alternatively, the flag can be cleared by writing a logical one to it. This flag is always cleared

when INT0 is configured as a level interrupt.

8.3.4 Pin Change Interrupt Control Register – PCICR

• Bit 7, 2 – Res: Reserved Bits

These bits are unused bits in the Atmel ATtiny87/167, and will always read as zero.

• Bit 1 - PCIE1: Pin Change Interrupt Enable 1

When the PCIE1 bit is set (one) and the I-bit in the status register (SREG) is set (one), pin change interrupt 1 is enabled. Any

change on any enabled PCINT15..8 pin will cause an interrupt. The corresponding interrupt of pin change interrupt request is

executed from the PCI1 interrupt vector. PCINT15..8 pins are enabled individually by the PCMSK1 register.

• Bit 0 - PCIE0: Pin Change Interrupt Enable 0

When the PCIE0 bit is set (one) and the I-bit in the status register (SREG) is set (one), pin change interrupt 0 is enabled. Any

change on any enabled PCINT7..0 pin will cause an interrupt. The corresponding interrupt of pin change interrupt request is

executed from the PCI0 Interrupt Vector. PCINT7..0 pins are enabled individually by the PCMSK0 register.

Bit 76543210

––––––INTF1INTF0EIFR

Read/WriteRRRRRRR/WR/W

Initial Value00000000

Bit 76543210

––––––PCIE1PCIE0PCICR

Read/WriteRRRRRRR/WR/W

Initial Value00000000

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8.3.5 Pin Change Interrupt Flag Register – PCIFR

• Bit 7, 2 – Res: Reserved Bits

These bits are unused bits in the Atmel® ATtiny87/167, and will always read as zero.

• Bit 1 - PCIF1: Pin Change Interrupt Flag 1

When a logic change on any PCINT15..8 pin triggers an interrupt request, PCIF1 becomes set (one). If the I-bit in SREG and

the PCIE1 bit in PCICR are set (one), the MCU will jump to the corresponding interrupt vector. The flag is cleared when the

interrupt routine is executed. Alternatively, the flag can be cleared by writing a logical one to it.

• Bit 0 - PCIF0: Pin Change Interrupt Flag 0

When a logic change on any PCINT7..0 pin triggers an interrupt request, PCIF0 becomes set (one). If the I-bit in SREG and

the PCIE0 bit in PCICR are set (one), the MCU will jump to the corresponding interrupt vector. The flag is cleared when the

interrupt routine is executed. Alternatively, the flag can be cleared by writing a logical one to it.

8.3.6 Pin Change Mask Register 1 – PCMSK1

• Bit 7..0 – PCINT15..8: Pin Change Enable Mask 15..8

Each PCINT15..8-bit selects whether pin change interrupt is enabled on the corresponding I/O pin. If PCINT15..8 is set and

the PCIE1 bit in PCICR is set, pin change interrupt is enabled on the corresponding I/O pin. If PCINT15..8 is cleared, pin

change interrupt on the corresponding I/O pin is disabled.

8.3.7 Pin Change Mask Register 0 – PCMSK0

• Bit 7..0 – PCINT7..0: Pin Change Enable Mask 7..0

Each PCINT7..0 bit selects whether pin change interrupt is enabled on the corresponding I/O pin. If PCINT7..0 is set and the

PCIE0 bit in PCICR is set, pin change interrupt is enabled on the corresponding I/O pin. If PCINT7..0 is cleared, pin change

interrupt on the corresponding I/O pin is disabled.

Bit 76543210

––––––PCIF1PCIF0PCIFR

Read/Write R R R R R R R/W R/W

Initial Value00000000

Bit 76543210

PCINT15 PCINT14 PCINT13 PCINT12 PCINT11 PCINT10 PCINT9 PCINT8 PCMSK1

Read/Write R/W R/W R/W R/W R/W R/W R/W R/W

Initial Value00000000

Bit 76543210

PCINT7 PCINT6 PCINT5 PCINT4 PCINT3 PCINT2 PCINT1 PCINT0 PCMSK0

Read/Write R/W R/W R/W R/W R/W R/W R/W R/W

Initial Value00000000

ATtiny87/ATtiny167 [DATASHEET]

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9. I/O-Ports

9.1 Introduction

All AVR® ports have true read-modify-write functionality when used as general digital I/O ports. This means that the direction

of one port pin can be changed without unintentionally changing the direction of any other pin with the SBI and CBI

instructions. The same applies when changing drive value (if configured as output) or enabling/disabling of pull-up resistors

(if configured as input). Each output buffer has symmetrical drive characteristics with both high sink and source capability.

The pin driver is strong enough to drive LED displays directly. All port pins have individually selectable pull-up resistors with

a supply-voltage invariant resistance. All I/O pins have protection diodes to both Vcc and Ground as indicated in Figure 9-1.

Refer to Section 22. “Electrical Characteristics” on page 222 for a complete list of parameters.

Figure 9-1. I/O Pin Equivalent Schematic

All registers and bit references in this section are written in general form. A lower case “x” represents the numbering letter for

the port, and a lower case “n” represents the bit number. However, when using the register or bit defines in a program, the

precise form must be used. For example, PORTB3 for bit no. 3 in Port B, here documented generally as PORTxn. The

physical I/O registers and bit locations are listed in Section 9.4 “Register Description for I/O Ports” on page 82.

Three I/O memory address locations are allocated for each port, one each for the data register – PORTx, data direction

register – DDRx, and the port input pins – PINx. The port input Pins I/O location is read only, while the data register and the

data direction register are read/write. However, writing a logic one to a bit in the PINx register, will result in a toggle in the

corresponding bit in the data register. In addition, the pull-up disable – PUD bit in MCUCR or PUDx in PORTCR disables the

pull-up function for all pins in all ports when set.

Using the I/O port as general digital I/O is described in Section 9.2 “Ports as General Digital I/O” on page 65. Most port pins

are multiplexed with alternate functions for the peripheral features on the device. How each alternate function interferes with

the port pin is described in Section 9.3 “Alternate Port Functions” on page 70. Refer to the individual module sections for a

full description of the alternate functions.

Note that enabling the alternate function of some of the port pins does not affect the use of the other pins in the port as

general digital I/O.

Cpin

Rpu

Pxn

Logic

See Figure

”General Digital I/O”

for Details

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9.2 Ports as General Digital I/O

The ports are bi-directional I/O ports with optional internal pull-ups. Figure 9-2 shows a functional description of one I/O-port

pin, here generically called Pxn.

Figure 9-2. General Digital I/O(1)

Notes: 1. WRx, WPx, WDx, RRx, RPx, and RDx are common to all pins within the same port. clkI/O, SLEEP, and PUD

are common to all ports.

9.2.1 Configuring the Pin

Each port pin consists of three register bits: DDxn, PORTxn, and PINxn. As shown in Section 9.4 “Register Description for

I/O Ports” on page 82, the DDxn bits are accessed at the DDRx I/O address, the PORTxn bits at the PORTx I/O address,

and the PINxn bits at the PINx I/O address.

The DDxn bit in the DDRx register selects the direction of this pin. If DDxn is written logic one, Pxn is configured as an output

pin. If DDxn is written logic zero, Pxn is configured as an input pin.

If PORTxn is written logic one when the pin is configured as an input pin, the pull-up resistor is activated. To switch the pull-

up resistor off, PORTxn has to be written logic zero or the pin has to be configured as an output pin. The port pins are tri-

stated when reset condition becomes active, even if no clocks are running.

If PORTxn is written logic one when the pin is configured as an output pin, the port pin is driven high (one). If PORTxn is

written logic zero when the pin is configured as an output pin, the port pin is driven low (zero).

WRx

RRx

WPx

Pxn

CLR

RESET

Synchronizer

DATA BUS

PORTxn

PINxn

RESET

RPx

WDx: WRITE DDRx

WRx:

WPx:

RPx:

RRx: READ PORTx REGISTER

READ PORTx PIN

WRITE PINx REGISTER

RDx:

WRITE PORTx

READ DDRx

PUD: PULLUP DISABLE

CLKI/O:

SLEEP:

I/O CLOCK

SLEEP CONTROL

RDx

CLKI/O

PUD

WDx

SLEEP

QCLR

DDxn

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9.2.2 Toggling the Pin

Writing a logic one to PINxn toggles the value of PORTxn, independent on the value of DDRxn. Note that the SBI assembler

instruction can be used to toggle one single bit in a port.

9.2.3 Break-before-make Switching

In the break-before-make mode when switching the DDRxn bit from input to output an immediate tri-state period lasting one

system clock cycle is introduced as indicated in Figure 9-3. For example, if the system clock is 4MHz and the DDRxn is

written to make an output, the immediate tri-state period of 250ns is introduced, before the value of PORTxn is seen on the

port pin. To avoid glitches it is recommended that the maximum DDRxn toggle frequency is two system clock cycles. The

break-before-make is a port-wise mode and it is activated by the port-wise BBMx enable bits. For further information about

the BBMx bits, see Section 9.3.2 “Port Control Register – PORTCR” on page 72. When switching the DDRxn bit from output

to input there is no immediate tri-state period introduced.

Figure 9-3. Break Before Make, Switching Between Input and Output

9.2.4 Switching Between Input and Output

When switching between tri-state ({DDxn, PORTxn} = 0, 0) and output high ({DDxn, PORTxn} = 1, 1), an intermediate state

with either pull-up enabled {DDxn, PORTxn} = 0, 1) or output low ({DDxn, PORTxn} = 1, 0) must occur. Normally, the pull-up

enabled state is fully acceptable, as a high-impudent environment will not notice the difference between a strong high driver

and a pull-up. If this is not the case, the PUD bit in the MCUCR Register or the PUDx bit in PORTCR register can be set to

disable all pull-ups in the port.

Switching between input with pull-up and output low generates the same problem. The user must use either the tri-state

({DDxn, PORTxn} = 0, 0) or the output high state ({DDxn, PORTxn} = 1, 1) as an intermediate step.

SYSTEM CLOCK

R16

R17

PORTx

INSTRUCTIONS

0x02

0x020x01 0x01

tri-state tri-state

tri-state

0x01

0x55

nopout DDRx, r16 out DDRx, r17

immediate tri-state cycle

DDRx

Px0

Px1

Or pan-wise PUDx bu in PORTCR register. 1. Note:

ATtiny87/ATtiny167 [DATASHEET]

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Table 9-1 summarizes the control signals for the pin value.

9.2.5 Reading the Pin Value

Independent of the setting of data direction bit DDxn, the port pin can be read through the PINxn register bit. As shown in

Figure 9-2, the PINxn register bit and the preceding latch constitute a synchronizer. This is needed to avoid metastability if

the physical pin changes value near the edge of the internal clock, but it also introduces a delay. Figure 9-4 shows a timing

diagram of the synchronization when reading an externally applied pin value. The maximum and minimum propagation

delays are denoted tpd,max and tpd,min respectively.

Figure 9-4. Synchronization when Reading an Externally Applied Pin Value

Consider the clock period starting shortly after the first falling edge of the system clock. The latch is closed when the clock is

low, and goes transparent when the clock is high, as indicated by the shaded region of the “SYNC LATCH” signal. The signal

value is latched when the system clock goes low. It is clocked into the PINxn register at the succeeding positive clock edge.

As indicated by the two arrows tpd,max and tpd,min, a single signal transition on the pin will be delayed between ½ and 1½

system clock period depending upon the time of assertion.

Table 9-1. Port Pin Configurations

DDxn PORTxn

PUD

(in MCUCR) (1) I/O Pull-up Comment

0 0 X Input No Tri-state (Hi-Z)

0 1 0 Input Yes Pxn will source current if ext. pulled low.

0 1 1 Input No Tri-state (Hi-Z)

1 0 X Output No Output low (Sink)

1 1 X Output No Output high (Source)

Note: 1. Or port-wise PUDx bit in PORTCR register.

SYSTEM CLK

INSTRUCTIONS

SYNC LATCH

PINxn

r17

XXX XXX

0x00 0xFF

in r17, PINx

tpd, max

tpd, min

Assembly Code Example‘n C Code Example

ATtiny87/ATtiny167 [DATASHEET]

7728H–AVR–03/14

When reading back a software assigned pin value, a nop instruction must be inserted as indicated in Figure 9-5. The out

instruction sets the “SYNC LATCH” signal at the positive edge of the clock. In this case, the delay tpd through the

synchronizer is 1 system clock period.

Figure 9-5. Synchronization When Reading a Software Assigned Pin Value

The following code example shows how to set port B pins 0 and 1 high, 2 and 3 low, and define the port pins from 4 to 7 as

input with pull-ups assigned to port pins 6 and 7. The resulting pin values are read back again, but as previously discussed,

a nop instruction is included to be able to read back the value recently assigned to some of the pins.

Note: 1. For the assembly program, two temporary registers are used to minimize the time from pull-ups are set on pins

0, 1, 6, and 7, until the direction bits are correctly set, defining bit 2 and 3 as low and redefining bits 0 and 1 as

strong high drivers.

Assembly Code Example(1)

...

; Define pull-ups and set outputs high

; Define directions for port pins

ldi r16,(1<<PB7)|(1<<PB6)|(1<<PB1)|(1<<PB0)

ldi r17,(1<<DDB3)|(1<<DDB2)|(1<<DDB1)|(1<<DDB0)

out PORTB,r16

out DDRB,r17

; Insert nop for synchronization

nop

; Read port pins

in r16,PINB

...

C Code Example

unsigned char i;

...

/* Define pull-ups and set outputs high */

/* Define directions for port pins */

PORTB = (1<<PB7)|(1<<PB6)|(1<<PB1)|(1<<PB0);

DDRB = (1<<DDB3)|(1<<DDB2)|(1<<DDB1)|(1<<DDB0);

/* Insert nop for synchronization*/

__no_operation();

/* Read port pins */

i = PINB;

...

SYSTEM CLK

INSTRUCTIONS

SYNC LATCH

PINxn

r16

r17

out PORTx, r16 nop

0x00 0xFF

0xFF

in r17, PINx

tpd

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9.2.6 Digital Input Enable and Sleep Modes

As shown in Figure 9-2, the digital input signal can be clamped to ground at the input of the Schmitt Trigger. The signal

denoted SLEEP in the figure, is set by the MCU sleep controller in power-down or power-save mode to avoid high power

consumption if some input signals are left floating, or have an analog signal level close to Vcc/2.

SLEEP is overridden for port pins enabled as external interrupt pins. If the external interrupt request is not enabled, SLEEP

is active also for these pins. SLEEP is also overridden by various other alternate functions as described in Section 9.3

“Alternate Port Functions” on page 70.

If a logic high level (“one”) is present on an asynchronous external interrupt pin configured as “interrupt on rising edge, falling

edge, or any logic change on pin” while the external interrupt is not enabled, the corresponding external Interrupt flag will be

set when resuming from the above mentioned Sleep mode, as the clamping in these sleep mode produces the requested

logic change.

9.2.7 Unconnected Pins

If some pins are unused, it is recommended to ensure that these pins have a defined level. Even though most of the digital

inputs are disabled in the deep sleep modes as described above, floating inputs should be avoided to reduce current

consumption in all other modes where the digital inputs are enabled (reset, active mode and idle mode).

The simplest method to ensure a defined level of an unused pin, is to enable the internal pull-up. In this case, the pull-up will

be disabled during reset. If low power consumption during reset is important, it is recommended to use an external pull-up or

pull-down. Connecting unused pins directly to Vcc or GND is not recommended, since this may cause excessive currents if

the pin is accidentally configured as an output.

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ATtiny87/ATtiny167 [DATASHEET]

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9.3 Alternate Port Functions

Most port pins have alternate functions in addition to being general digital I/Os. Figure 9-6 shows how the port pin control

signals from the simplified Figure 9-2 on page 65 can be overridden by alternate functions. The overriding signals may not

be present in all port pins, but the figure serves as a generic description applicable to all port pins in the AVR microcontroller

family.

Figure 9-6. Alternate Port Functions(1)

Note: 1. WRx, WPx, WDx, RRx, RPx, and RDx are common to all pins within the same port. clkI/O, SLEEP, and PUD

are common to all ports. All other signals are unique for each pin.

WRx

RRx

WPx

PTOExn

Pxn

CLR

RESET

Synchronizer

DATA BUS

PORTxn

DSET

CLR CLR

PINxn

RESET

RPx

Pxn PULL-UP OVERRIDE ENABLE

Pxn PULL-UP OVERRIDE VALUE

PUD: PULL-UP DISABLEPUOExn:

Pxn PORT VALUE OVERRIDE VALUEPVOVxn:

Pxn PORT VALUE OVERRIDE ENABLEPVOExn:

Pxn DATA DIRECTION OVERRIDE ENABLE

Pxn DATA DIRECTION OVERRIDE VALUE

DDOExn:

DDOVxn:

SLEEP CONTROLSLEEP:

Pxn, PORT TOGGLE OVERRIDE ENABLEPTOExn:

Pxn DIGITAL INPUT ENABLE OVERRIDE VALUEDIEOVxn:

Pxn DIGITAL INPUT ENABLE OVERRIDE ENABLEDIEOExn:

I/O CLOCK

RDx:

RPx:

WRITE PINx

WRx:

ANALOG INPUT/OUTPUT PIN n ON PORTx

DIGITAL INPUT PIN n ON PORTx

RRx: READ PORTx REGISTER

WPx:

WRITE PORTx

AIOxn:

DIxn:

READ PORTx PIN

WDx:

READ DDRx

WRITE DDRxPUOVxn:

RDx

CLKI/O

DIxn

AIOxn

CLK:I/O

DIEOVxn

DIEOExn

PVOExn

DDOExn

PVOVxn

PUOExn

PUOVxn

1DDOVxn

SLEEP

PUD

WDx

QCLR

DDxn

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Table 9-2 summarizes the function of the overriding signals. The pin and port indexes from Figure 9-6 are not shown in the

succeeding tables. The overriding signals are generated internally in the modules having the alternate function.

The following subsections shortly describe the alternate functions for each port, and relate the overriding signals to the

alternate function. Refer to the alternate function description for further details.

Table 9-2. Generic Description of Overriding Signals for Alternate Functions

Signal Name Full Name Description

PUOE Pull-up override enable

If this signal is set, the pull-up enable is controlled by the PUOV signal. If

this signal is cleared, the pull-up is enabled when {DDxn, PORTxn, (PUD or

PDUx)} = 0, 1, 0.

PUOV Pull-up override value

If PUOE is set, the pull-up is enabled/disabled when PUOV is set/cleared,

regardless of the setting of the DDxn, PORTxn, PUD and PUDx register

bits.

DDOE Data direction override

enable

If this signal is set, the Output Driver Enable is controlled by the DDOV

signal. If this signal is cleared, the Output driver is enabled by the DDxn

DDOV Data direction override

value

If DDOE is set, the output driver is enabled/disabled when DDOV is

set/cleared, regardless of the setting of the DDxn register bit.

PVOE Port value override

enable

If this signal is set and the output driver is enabled, the port value is

controlled by the PVOV signal. If PVOE is cleared, and the output driver is

enabled, the port Value is controlled by the PORTxn register bit.

PVOV Port value override value If PVOE is set, the port value is set to PVOV, regardless of the setting of the

PORTxn register bit.

PTOE Port toggle override

enable If PTOE is set, the PORTxn register bit is inverted.

DIEOE Digital input enable

override enable

If this bit is set, the digital input enable is controlled by the DIEOV signal. If

this signal is cleared, the digital input enable is determined by MCU state

(normal mode, sleep mode).

DIEOV Digital input enable

override value

If DIEOE is set, the digital input is enabled/disabled when DIEOV is

set/cleared, regardless of the MCU state (normal mode, sleep mode).

DI Digital Input

This is the digital input to alternate functions. In the figure, the signal is

connected to the output of the Schmitt Trigger but before the synchronizer.

Unless the digital input is used as a clock source, the module with the

alternate function will use its own synchronizer.

AIO Analog input/output This is the analog input/output to/from alternate functions. The signal is

connected directly to the pad, and can be used bi-directionally.

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9.3.1 MCU Control Register – MCUCR

• Bit 4 – PUD: Pull-up Disable

When this bit is written to one, the pull-ups in the I/O ports are disabled even if the DDxn and PORTxn registers are

configured to enable the pull-ups ({DDxn, PORTxn} = 0, 1). See Section 9.2.1 “Configuring the Pin” on page 65 for more

details about this feature.

9.3.2 Port Control Register – PORTCR

• Bits 5, 4 – BBMx: Break-Before-Make Mode Enable

When these bits are written to one, the port-wise break-before-make mode is activated. The intermediate tri-state cycle is

then inserted when writing DDRxn to make an output. For further information, see Section 9.2.3 “Break-before-make

Switching” on page 66.

• Bits 1, 0 – PUDx: Port-Wise Pull-up Disable

When these bits are written to one, the port-wise pull-ups in the defined I/O ports are disabled even if the DDxn and PORTxn

registers are configured to enable the pull-ups ({DDxn, PORTxn} = 0, 1). The port-wise pull-up disable bits are ORed with the

global pull-up disable bit (PUD) from the MCUCR register. See See ”Configuring the Pin” on page 65. for more details about

this feature.

Bit 7 6 5 4 3 2 1 0

–BODS BODSE PUD – – – – MCUCR

Read/Write R R/W R/W R/W R R R R

Initial Value 0 0 0 0 0 0 0 0

Bit 7 6 5 4 3 2 1 0

- - BBMB BBMA - - PUDB PUDA PORTCR

Read/Write R/W R/W R/W R/W R/W R/W R/W R/W

Initial Value 0 0 0 0 0 0 0 0

alternate allemale alternate alternate alternate AtmeL

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9.3.3 Alternate Functions of Port A

The Port A pins with alternate functions are shown in Table 9-3.

Table 9-3. Port A Pins Alternate Functions

Port Pin Alternate Function

PA7

PCINT7 (pin change interrupt 7)

ADC7 (ADC input channel 7)

AIN1 (analog comparator positive input)

XREF (internal voltage reference output)

AREF (external voltage reference input)

PA6

PCINT6 (pin change interrupt 6)

ADC6 (ADC input channel 6)

AIN0 (analog comparator negative Input)

SS (SPI slave select input)

PA5

PCINT5 (pin change interrupt 5)

ADC5 (ADC input channel 5)

T1 (timer/counter1 clock input)

USCK (three-wire mode USI alternate clock input)

SCL (two-wire mode USI alternate clock input)

SCK (SPI master clock)

PA4

PCINT4 (pin change interrupt 4)

ADC4 (ADC input channel 4)

ICP1 (timer/counter1 input capture trigger)

DI (three-wire mode USI alternate data input)

SDA (two-wire mode USI alternate data input / output)

MOSI (SPI master output / slave input)

PA3

PCINT3 (pin change interrupt 3)

ADC3 (ADC input channel 3)

ISRC (current source pin)

INT1 (external interrupt1 input)

PA2

PCINT2 (pin change interrupt 2)

ADC2 (ADC input channel 2)

OC0A (output compare and PWM output A for timer/counter0)

DO (three-wire mode USI alternate data output)

MISO (SPI master input / slave output)

PA1

PCINT1 (pin change interrupt 1)

ADC1 (ADC input channel 1)

TXD (UART transmit pin)

TXLIN (LIN transmit pin)

PA0

PCINT0 (pin change interrupt 0)

ADC0 (ADC input channel 0)

RXD (UART receive pin)

RXLIN (LIN receive pin)

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The alternate pin configuration is as follows:

• PCINT7/ADC7/AIN1/XREF/AREF – Port A, Bit7

PCINT7: pin change interrupt, source 7.

ADC7: analog to digital converter, channel 7.

AIN1: analog comparator positive input. This pin is directly connected to the positive input of the analog comparator.

XREF: internal voltage reference output. The internal voltage reference 2.56V or 1.1V is output when XREFEN is set and if

either 2.56V or 1.1V is used as reference for ADC conversion. When XREF output is enabled, the pin port pull-up and digital

output driver are turned off.

AREF: external voltage reference input for ADC. The pin port pull-up and digital output driver are disabled when the pin is

used as an external voltage reference input for ADC or as when the pin is only used to connect a bypass capacitor for the

voltage reference of the ADC.

• PCINT6/ADC6/AIN0/SS – Port A, Bit6

PCINT6: pin change interrupt, source 6.

ADC6: analog to digital converter, channel 6.

AIN0: analog comparator negative input. This pin is directly connected to the negative input of the analog comparator.

SS: SPI slave select input. When the SPI is enabled as a slave, this pin is configured as an input regardless of the setting of

DDA6. As a slave, the SPI is activated when this pin is driven low. When the SPI is enabled as a master, the data direction

of this pin is controlled by DDA6. When the pin is forced to be an input, the pull-up can still be controlled by the PORTA6 bit.

• PCINT5/ADC5/T1/USCK/SCL/SCK – Port A, Bit5

PCINT5: pin change interrupt, source 5.

ADC5: analog to digital converter, channel 5.

T1: timer/counter1 clock input.

USCK: three-wire mode USI clock input.

SCL: two-wire mode USI clock input.

SCK: SPI master clock output, slave clock input pin. When the SPI is enabled as a slave, this pin is configured as an input

regardless of the setting of DDA5. When the SPI is enabled as a master, the data direction of this pin is controlled by DDA5.

When the pin is forced to be an input, the pull-up can still be controlled by the PORTA5 bit.

• PCINT4/ADC4/ICP1/DI/SDA/MOSI – Port A, Bit 4

PCINT4: pin change interrupt, source 4.

ADC4: analog to digital converter, channel 4.

ICP1: timer/counter1 input capture trigger. The PA3 pin can act as an input capture pin for timer/counter1.

DI: three-wire mode USI data input. USI three-wire mode does not override normal port functions, so pin must be configure

as an input for DI function.

SDA: two-wire mode serial interface (USI) data input / output.

MOSI: SPI master output / slave input. When the SPI is enabled as a slave, this pin is configured as an input regardless of

the setting of DDA3. When the SPI is enabled as a master, the data direction of this pin is controlled by DDA3. When the pin

is forced by the SPI to be an input, the pull-up can still be controlled by the PORTA3 bit.

• PCINT3/ADC3/ISRC/INT1 – Port A, Bit 3

PCINT3: pin change interrupt, source 3.

ADC3: analog to digital converter, channel 3.

ISCR: current source output pin. While current is sourced by the current source module, the user can use the analog to

digital converter channel 4 (ADC4) to measure the pin voltage.

INT1: external interrupt, source 1. The PA4 pin can serve as an external interrupt source.

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PCINT2/ADC2/OC0A/DO/MISO – Port A, Bit 2

PCINT2: pin change interrupt, source 2.

ADC2: analog to digital converter, channel 2.

OC0A: output compare match A or output PWM A for timer/counter0. The pin has to be configured as an output (DDA2 set

(one)) to serve these functions.

DO: three-wire mode USI data output. Three-wire mode data output overrides PORTA2 and it is driven to the port when the

data direction bit DDA2 is set. PORTA2 still enables the pull-up, if the direction is input and PORTA2 is set (one).

MISO: master data input, slave data output pin for SPI channel. When the SPI is enabled as a master, this pin is configured

as an input regardless of the setting of DDA2. When the SPI is enabled as a slave, the data direction of this pin is controlled

by DDA2. When the pin is forced to be an input, the pull-up can still be controlled by PORTA2.

• PCINT1/ADC1/TXD/TXLIN – Port A, Bit 1

PCINT1: pin change interrupt, source 1.

ADC1: analog to digital converter, channel 1.

TXD: UART transmit pin. When the UART transmitter is enabled, this pin is configured as an output regardless the value of

DDA1. PORTA1 still enables the pull-up, if the direction is input and PORTA2 is set (one).

TXLIN: LIN transmit pin. When the LIN is enabled, this pin is configured as an output regardless the value of DDA1.

PORTA1 still enables the pull-up, if the direction is input and PORTA2 is set (one).

• PCINT0/ADC0/RXD/RXLIN – Port A, Bit 0

PCINT0: pin change interrupt, source 0.

ADC0: analog to digital converter, channel 0.

RXD: UART receive pin. When the UART receiver is enabled, this pin is configured as an input regardless of the value of

DDA0. When the pin is forced to be an input, a logical one in PORTA0 will turn on the internal pull-up.

RXLIN: LIN receive pin. When the LIN is enabled, this pin is configured as an input regardless of the value of DDA0. When

the pin is forced to be an input, a logical one in PORTA0 will turn on the internal pull-up.

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Table 9-4 and Table 9-5 on page 77 relate the alternate functions of Port A to the overriding signals shown in Figure 9-6 on

page 70.

Table 9-4. Overriding Signals for Alternate Functions in PA7..PA4

Signal

Name

PA7/PCINT7/

ADC7/AIN1

/XREF/AREF

PA6/PCINT6/

ADC6/AIN0/SS

PA5/PCINT5/ADC5/

T1/USCK/SCL/SCK

PA4/PCINT4/ADC4/

ICP1/DI/SDA/MOSI

PUOE 0SPE & MSTR SPE & MSTR SPE & MSTR

PUOV 0PORTA6 & PUD PORTA5 & PUD PORTA4 & PUD

DDOE 0SPE & MSTR (SPE & MSTR) |

(USI_2_WIRE & USIPOS)

(SPE & MSTR) |

(USI_2_WIRE & USIPOS)

DDOV 0 0 (USI_SCL_HOLD | PORTA5)

& DDRA6

{(SPE & MSTR) ?

(0) :

(USI_SHIFTOUT | PORTA4)

& DDRA4) }

PVOE 0 0

(SPE & MSTR) |

(USI_2_WIRE & USIPOS

& DDRA5)

(SPE & MSTR) |

(USI_2_WIRE & USIPOS

& DDRA4)

PVOV 0 0

{(SPE & MSTR) ?

(SCK_OUTPUT) :

~ (USI_2_WIRE & USIPOS

& DDRA5) }

{(SPE & MSTR) ?

(MOSI_OUTPUT) :

~ (USI_2_WIRE & USIPOS

& DDRA4) }

PTOE 0 0 USI_PTOE & USIPOS 0

DIEOE ADC7D |

(PCIE0 & PCMSK07)

ADC6D |

(PCIE0 & PCMSK06)

ADC5D |

(USISIE & USIPOS) |

(PCIE0 & PCMSK05)

ADC4D |

(USISIE & USIPOS) |

(PCIE0 & PCMSK04)

DIEOV PCIE0 & PCMSK07 PCIE0 & PCMSK06 (USISIE & USIPOS) |

(PCIE0 & PCMSK05)

(USISIE & USIPOS) |

(PCIE0 & PCMSK04)

DI PCINT7 PCINT6 -/- SS PCINT5 -/- T1

-/- USCK -/- SCL -/- SCK

PCINT4 -/- ICP1

-/- DI -/- SDA -/- MOSI

AIO ADC7 -/- AIN1 -/-

XREF -/- AREF ADC6 -/- AIN0 ADC5 ADC4

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Table 9-5. Overriding Signals for Alternate Functions in PA3..PA0

Signal

Name

PA3/PCINT3/ADC3/

ISRC/INT1

PA2/PCINT2/ADC2/

OC0A/DO/MISO

PA1/PCINT1/ADC1/

TXD/TXLIN

PA0/PCINT0/ADC0/

RXD/RXLIN

PUOE 0SPE & MSTR LIN_TX_ENABLE LIN_RX_ENABLE

PUOV PORTA3 & PUD PORTA2 & PUD {(LIN_TX_ENABLE) ?

(0) : (PORTA1 & PUD) }PORTA0 & PUD

DDOE 0SPE & MSTR LIN_TX_ENABLE LIN_RX_ENABLE

DDOV 0 0 LIN_TX_ENABLE 0

PVOE 0

(SPE & MSTR) |

(USI_2_WIRE & USI_3_WIRE &

USIPOS) |

OC0A

LIN_TX_ENABLE 0

PVOV 0

{(SPE & MSTR) ?

(MISO_OUTPUT) :

( ( USI_2_WIRE & USI_3_WIRE

& USIPOS ) ?

(USI_SHIFTOUT) : (OC0A) ) }

{(LIN_TX_ENABLE) ?

(LIN_TX) : (0) }0

PTOE 0 0 0 0

DIEOE

ADC3D |

INT1_ENABLE |

(PCIE0 & PCMSK03)

ADC2D |

(PCIE0 & PCMSK02)

ADC1D |

(PCIE0 & PCMSK01)

ADC0D |

(PCIE0 & PCMSK00)

DIEOV INT1_ENABLE |

(PCIE0 & PCMSK03) PCIE0 & PCMSK02 PCIE0 & PCMSK01 PCIE0 & PCMSK00

DI PCINT3 -/- INT1 PCINT2 -/- MISO PCINT1 PCINT0

AIO ADC3 -/- ISRC ADC2 ADC1 ADC0

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9.3.4 Alternate Functions of Port B

The Port B pins with alternate functions are shown in Table 9-6.

Table 9-6. Port B Pins Alternate Functions

Port Pin Alternate Functions

PB7

PCINT15 (pin change interrupt 15)

ADC10 (ADC input channel 10)

OC1BX (output compare and PWM output B-X for timer/counter1)

RESET (reset input pin)

dW (debugWIRE I/O)

PB6

PCINT14 (pin change interrupt 14)

ADC9 (ADC input channel 9)

OC1AX (0utput compare and PWM Output A-X for timer/counter1)

INT0 (external interrupt0 input)

PB5

PCINT13 (pin change Iiterrupt 13)

ADC8 (ADC input channel 8)

OC1BW (output compare and PWM output B-W for timer/counter1)

XTAL2 (chip clock oscillator pin 2)

CLKO (system clock output)

PB4

PCINT12 (pin change interrupt 12)

OC1AW (output compare and PWM output A-W for timer/counter1)

XTAL1 (chip clock oscillator pin 1)

CLKI (external clock input)

PB3 PCINT11 (pin change interrupt 11)

OC1BV (output compare and PWM Output B-V for timer/counter1)

PB2

PCINT10 (pin change interrupt 10)

OC1AV (output compare and PWM Output A-V for timer/counter1)

USCK (three-wire mode USI default clock nput)

SCL (two-wire mode USI default clock input)

PB1

PCINT9 (pin change interrupt 9)

OC1BU (output compare and PWM output B-U for timer/counter1)

DO (three-wire mode USI default data output)

PB0

PCINT8 (pin change interrupt 8)

OC1AU (output compare and PWM Output A-U for timer/counter1)

DI (three-wire mode USI default data input)

SDA (two-wire mode USI default data input / output)

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The alternate pin configuration is as follows:

• PCINT15/ADC10/OC1BX/RESET/dW – Port B, Bit 7

PCINT15: pin change interrupt, source 15.

ADC10: analog to digital converter, channel 10.

OC1BX: output compare and PWM output B-X for timer/counter1. The PB7 pin has to be configured as an output (DDB7 set

(one)) to serve this function. The OC1BX pin is also the output pin for the PWM mode timer function (c.f. OC1BX bit of

TCCR1D register).

RESET: reset input pin. When the RSTDISBL fuse is programmed, this pin functions as a normal I/O pin, and the part will

have to rely on power-on reset and brown-out reset as its reset sources. When the RSTDISBL fuse is unprogrammed, the

reset circuitry is connected to the pin, and the pin can not be used as an I/O pin.

If PB7 is used as a reset pin, DDB7, PORTB7 and PINB7 will all read 0.

dW: when the debugWIRE enable (DWEN) Fuse is programmed and lock bits are unprogrammed, the RESET port pin is

configured as a wire-AND (open-drain) bi-directional I/O pin with pull-up enabled and becomes the communication gateway

between target and emulator.

• PCINT14/ADC9/OC1AX/INT0 – Port B, Bit 6

PCINT14: pin change interrupt, source 14.

ADC9: analog to digital converter, channel 9.

OC1AX: output compare and PWM Output A-X for timer/counter1. The PB6 pin has to be configured as an output (DDB6 set

(one)) to serve this function. The OC1AX pin is also the output pin for the PWM mode timer function (c.f. OC1AX bit of

TCCR1D register).

INT0: external interrupt0 Input. The PB6 pin can serve as an external interrupt source.

• PCINT13/ADC8/OC1BW/XTAL2/CLKO – Port B, Bit 5

PCINT13: pin change interrupt, source 13.

ADC8: analog to digital converter, channel 8.

OC1BW: output compare and PWM Output B-W for timer/counter1. The PB5 pin has to be configured as an output (DDB5

set (one)) to serve this function. The OC1BW pin is also the output pin for the PWM mode timer function (c.f. OC1BW bit of

TCCR1D register).

XTAL2: chip clock oscillator pin 2. Used as clock pin for crystal oscillator or low-frequency crystal oscillator. When used as a

clock pin, the pin can not be used as an I/O pin.

CLKO: divided system clock output. The divided system clock can be output on the PB5 pin. The divided system clock will be

output if the CKOUT fuse is programmed, regardless of the PORTB5 and DDB5 settings. It will also be output during reset.

• PCINT12/OC1AW/XTAL1/CLKI – Port B, Bit 4

PCINT12: pin change interrupt, source 12.

OC1AW: output compare and PWM Output A-W for timer/counter1. The PB4 pin has to be configured as an output (DDB4

set (one)) to serve this function. The OC1AW pin is also the output pin for the PWM mode timer function (c.f. OC1AW bit of

TCCR1D register).

XTAL1: chip clock oscillator pin 1. Used for all chip clock sources except internal calibrated RC oscillator. When used as a

clock pin, the pin can not be used as an I/O pin.

CLKI: external clock input. When used as a clock pin, the pin can not be used as an I/O pin.

Note: If PB4 is used as a clock pin (XTAL1 or CLKI), DDB4, PORTB4 and PINB4 will all read 0.

• PCINT11/OC1BV – Port B, Bit 3

PCINT11: pin change interrupt, source 11.

OC1BV: output compare and PWM output B-V for timer/counter1. The PB3 pin has to be configured as an output (DDB3 set

(one)) to serve this function. The OC1BV pin is also the output pin for the PWM mode timer function (c.f. OC1BV bit of

TCCR1D register).

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• PCINT10/OC1AV/USCK/SCL – Port B, Bit 2

PCINT10: pin change interrupt, source 10.

OC1AV: output compare and PWM Output A-V for timer/counter1. The PB2 pin has to be configured as an output (DDB2 set

(one)) to serve this function. The OC1AV pin is also the output pin for the PWM mode timer function (c.f. OC1AV bit of

TCCR1D register).

USCK: three-wire mode USI clock input.

SCL: two-wire mode USI clock input.

• PCINT9/OC1BU/DO – Port B, Bit 1

PCINT9: pin change interrupt, source 9.

OC1BU: output compare and PWM output B-U for timer/counter1. The PB1 pin has to be configured as an output (DDB1 set

(one)) to serve this function. The OC1BU pin is also the output pin for the PWM mode timer function (c.f. OC1BU bit of

TCCR1D register).

DO: three-wire mode USI data output. Three-wire mode data output overrides PORTB1 and it is driven to the port when the

data direction bit DDB1 is set. PORTB1 still enables the pull-up, if the direction is input and PORTB1 is set (one).

• PCINT8/OC1AU/DI/SDA – Port B, Bit 0

IPCINT8: pin change interrupt, source 8.

OC1AU: output compare and PWM output A-U for timer/counter1. The PB0 pin has to be configured as an output (DDB0 set

(one)) to serve this function. The OC1AU pin is also the output pin for the PWM mode timer function (c.f. OC1AU bit of

TCCR1D register).

DI: three-wire mode USI data input. USI three-wire mode does not override normal port functions, so pin must be configure

as an input for DI function.

SDA: two-wire mode serial interface (USI) data input / output.

Table 9-7 and Table 9-8 on page 81 relate the alternate functions of Port B to the overriding signals shown in Figure 9-6 on

page 70.

Table 9-7. Overriding Signals for Alternate Functions in PB7..PB4

Signal

Name

PB7/PCINT15/ADC10/

OC1BX/RESET/dW

PB6/PCINT14/ADC9/

OC1AX/INT0

PB5/PCINT13/ADC8/

OC1BW/XTAL2/CLKO

PB4/PCINT12/

OC1AW/XTAL1/CLKI

PUOE 0 0 0 0

PUOV 0 0 0 0

DDOE 0 0 0 0

DDOV 0 0 0 0

PVOE OC1B_ENABLE & OC1BX OC1A_ENABLE & OC1AX OC1B_ENABLE &

OC1BW

OC1A_ENABLE &

OC1AW

PVOV OC1B OC1A OC1B OC1A

PTOE 0 0 0 0

DIEOE ADC10D |

(PCIE1 & PCMSK15)

ADC9D |

INT0_ENABLE |

(PCIE1 & PCMSK14)

ADC8D |

(PCIE1 & PCMSK13) (PCIE1 & PCMSK13)

DIEOV PCIE1 & PCMSK15 INT0_ENABLE |

(PCIE1 & PCMSK14) PCIE1 & PCMSK13 1

DI PCINT15 PCINT14 -/- INT1 PCINT13 PCINT12

AIO RESET -/- ADC10 -/- ADC9 -/- ISRC ADC8 -/- XTAL2 XTAL1 -/- CLKI

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Table 9-8. Overriding Signals for Alternate Functions in PB3..PB0

Signal

Name

PB3/PCINT11/

OC1BV

PB2/PCINT10/

OC1AV/USCK/SCL

PB1/PCINT9/

OC1BU/DO

PB0/IPCINT8/

OC1AU/DI/SDA

PUOE 0 0 0 0

PUOV 0 0 0 0

DDOE 0(USI_2_WIRE & USIPOS) 0 (USI_2_WIRE &

USIPOS)

DDOV 0

(USI_SCL_HOLD |

PORTB2)

& DDRB2

0(USI_SHIFTOUT |

PORTB0) & DDRB0)

PVOE OC1B_ENABLE &

OC1BV

(USI_2_WIRE &

USIPOS &

DDRB2) |

(OC1A_ENABLE & OC1AV)

(USI_2_WIRE &

USI_3_WIRE &

USIPOS) |

(OC1B_ENABLE & OC1BU)

(USI_2_WIRE &

USIPOS &

DDRB0) |

(OC1A_ENABLE & OC1AU)

PVOV OC1B

{(USI_2_WIRE &

USIPOS &

DDRB2) ?

(0) : (OC1A) }

{(USI_2_WIRE &

USI_3_WIRE &

USIPOS) ?

(USI_SHIFTOUT) : (OC1B) }

{(USI_2_WIRE &

USIPOS &

DDRB0) ?

(0) : (OC1A) }

PTOE 0USI_PTOE & USIPOS 0 0

DIEOE PCIE1 & PCMSK11 (USISIE & USIPOS) |

(PCIE1 & PCMSK10) PCIE1 & PCMSK9 (USISIE & USIPOS) |

(PCIE1 & PCMSK8)

DIEOV 1(USISIE & USIPOS) |

(PCIE1 & PCMSK10) 1(USISIE & USIPOS) |

(PCIE1 & PCMSK8)

DI PCINT11 PCINT10 -/- USCK -/- SCL PCINT9 PCINT8 -/- DI -/- SDA

AIO 0 0 0 0

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9.4 Register Description for I/O Ports

9.4.1 Port A Data Register – PORTA

9.4.2 Port A Data Direction Register – DDRA

9.4.3 Port A Input Pins Register – PINA

9.4.4 Port B Data Register – PORTB

9.4.5 Port B Data Direction Register – DDRB

9.4.6 Port B Input Pins Register – PINB

Bit 76543210

PORTA7 PORTA6 PORTA5 PORTA4 PORTA3 PORTA2 PORTA1 PORTA0 PORTA

Read/Write R/W R/W R/W R/W R/W R/W R/W R/W

Initial Value 0 0 0 0 0 0 0 0

Bit 76543210

DDA7 DDA6 DDA5 DDA4 DDA3 DDA2 DDA1 DDA0 DDRA

Read/Write R/W R/W R/W R/W R/W R/W R/W R/W

Initial Value 0 0 0 0 0 0 0 0

Bit 76543210

PINA7 PINA6 PINA5 PINA4 PINA3 PINA2 PINA1 PINA0 PINA

Read/Write R/(W) R/(W) R/(W) R/(W) R/(W) R/(W) R/(W) R/(W)

Initial Value N/A N/A N/A N/A N/A N/A N/A N/A

Bit 76543210

PORTB7 PORTB6 PORTB5 PORTB4 PORTB3 PORTB2 PORTB1 PORTB0 PORTB

Read/Write R/W R/W R/W R/W R/W R/W R/W R/W

Initial Value00000000

Bit 76543210

DDB7 DDB6 DDB5 DDB4 DDB3 DDB2 DDB1 DDB0 DDRB

Read/Write R/W R/W R/W R/W R/W R/W R/W R/W

Initial Value 0 0 0 0 0 0 0 0

Bit 76543210

PINB7 PINB6 PINB5 PINB4 PINB3 PINB2 PINB1 PINB0 PINB

Read/Write R/(W) R/(W) R/(W) R/(W) R/(W) R/(W) R/(W) R/(W)

Initial Value N/A N/A N/A N/A N/A N/A N/A N/A

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10. 8-bit Timer/Counter0 and Asynchronous Operation

Timer/counter0 is a general purpose, single channel, 8-bit timer/counter module. The main features are:

10.1 Features

●Single channel counter

●Clear timer on compare match (auto reload)

●Glitch-free, phase correct pulse width modulator (PWM)

●Frequency generator

●10-bit Clock prescaler

●Overflow and compare match interrupt sources (TOV0 and OCF0A)

●Allows clocking from external crystal (i.e. 32kHz watch crystal) independent of the I/O clock

10.2 Overview

Many register and bit references in this section are written in general form.

●A lower case “n” replaces the timer/counter number, in this case 0. However, when using the register or bit defines in

a program, the precise form must be used, i.e., TCNT0 for accessing timer/counter0 counter value and so on.

●A lower case “x” replaces the output compare unit channel, in this case A. However, when using the register or bit

defines in a program, the precise form must be used, i.e., OCR0A for accessing timer/counter0 output compare

channel A value and so on.

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A simplified block diagram of the 8-bit timer/counter is shown in Figure 10-1. For the actual placement of I/O pins, refer to

Section 1.6 “Pin Configuration” on page 6. CPU accessible I/O registers, including I/O bits and I/O pins, are shown in bold.

The device-specific I/O register and bit locations are listed in the Section 10.11 “8-bit Timer/Counter Register Description” on

page 95.

Figure 10-1. 8-bit Timer/Counter0 Block Diagram

The timer/counter (TCNT0) and output compare register (OCR0A) are 8-bit registers. Interrupt request (shorten as Int.Req.)

signals are all visible in the timer interrupt flag register (TIFR0). All interrupts are individually masked with the timer interrupt

mask register (TIMSK0). TIFR0 and TIMSK0 are not shown in the figure.

The timer/counter can be clocked internally, via the prescaler, or asynchronously clocked from the XTAL1/2 pins, as detailed

later in this section. The asynchronous operation is controlled by the asynchronous status register (ASSR). The clock select

logic block controls which clock source the timer/counter uses to increment (or decrement) its value. The timer/counter is

inactive when no clock source is selected. The output from the clock select logic is referred to as the timer clock (clkT0).

The double buffered output compare register (OCR0A) is compared with the timer/counter value at all times. The result of

the compare can be used by the waveform generator to generate a PWM or variable frequency output on the output

compare pin (OC0A). Section 10.5 “Output Compare Unit” on page 86 for details. The compare match event will also set the

compare flag (OCF0A) which can be used to generate an output compare interrupt request.

TOP

= 0 = 0xFF

BOTTOM

Status flags

Synchronized Status flags

asynchronous mode

select (ASn)

Synchronization Unit

XTAL2

XTAL1

OCnx

TCNTn

Timer/Counter

count

clear

direction

OCRnx

ASSRn

TCCRnx

DATA BUS

Control Logic

Prescaler

Waveform

Generation

Oscillator

clkTn

clkI/O

clkASY

TOVn

(Int. Req.)

OCnx

(Int. Req.)

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10.2.1 Definitions

The following definitions are used extensively throughout the section:

●BOTTOM: The counter reaches the BOTTOM when it becomes zero (0x00).

●MAX: The counter reaches its MAXimum when it becomes 0xFF (decimal 255).

●TOP: The counter reaches the TOP when it becomes equal to the highest value in the count sequence. The TOP

value can be assigned to be the fixed value 0xFF (MAX) or the value stored in the OCR0A register. The assignment is

dependent on the mode of operation.

10.3 Timer/Counter Clock Sources

The timer/counter can be clocked by an internal synchronous or an external asynchronous clock source. The clock source is

selected by the clock select logic which is controlled by the clock select (CS02:0) bits located in the timer/counter control

register (TCCR0).The clock source clkT0 is by default equal to the MCU clock, clkI/O. When the AS0 bit in the ASSR register

is written to logic one, the clock source is taken from the timer/counter oscillator connected to XTAL1 and XTAL2 or directly

from XTAL1. For details on asynchronous operation, see Section 10.11.4 “Asynchronous Status Register – ASSR” on page

98. For details on clock sources and prescaler, see Section 10.10 “Timer/Counter0 Prescaler” on page 95.

10.4 Counter Unit

The main part of the 8-bit timer/counter is the programmable bi-directional counter unit. Figure 10-2 shows a block diagram

of the counter and its surrounding environment.

Figure 10-2. Counter Unit Block Diagram

Signal description (internal signals):

count Increment or decrement TCNT0 by 1.

direction Selects between increment and decrement.

clear Clear TCNT0 (set all bits to zero).

clkT0 Timer/Counter0 clock.

top Signalizes that TCNT0 has reached maximum value.

bottom Signalizes that TCNT0 has reached minimum value (zero).

Depending on the mode of operation used, the counter is cleared, incremented, or decremented at each timer clock (clkT0).

clkT0 can be generated from an external or internal clock source, selected by the clock Select bits (CS02:0). When no clock

source is selected (CS02:0 = 0) the timer is stopped. However, the TCNT0 value can be accessed by the CPU, regardless of

whether clkT0 is present or not. A CPU write overrides (has priority over) all counter clear or count operations.

The counting sequence is determined by the setting of the WGM01 and WGM00 bits located in the timer/counter control

generated on the output compare output OC0A. For more details about advanced counting sequences and waveform

generation, see Section 10.7 “Modes of Operation” on page 88.

The timer/counter overflow flag (TOV0) is set according to the mode of operation selected by the WGM01:0 bits. TOV0 can

be used for generating a CPU interrupt.

topbottom

TOVn

(Int. Req.)

DATA BUS

Control LogicTCNTn clkTn clkTnS

clear

count

direction

clkI/O

Prescaler

Oscillator

XTAL2

XTAL1

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10.5 Output Compare Unit

The 8-bit comparator continuously compares TCNT0 with the output compare register (OCR0A). Whenever TCNT0 equals

OCR0A, the comparator signals a match. A match will set the output compare flag (OCF0A) at the next timer clock cycle. If

enabled (OCIE0A = 1), the output compare flag generates an output compare interrupt. The OCF0A flag is automatically

cleared when the interrupt is executed. Alternatively, the OCF0A flag can be cleared by software by writing a logical one to

its I/O bit location. The waveform generator uses the match signal to generate an output according to operating mode set by

the WGM01:0 bits and compare output mode (COM0A1:0) bits. The max and bottom signals are used by the waveform

generator for handling the special cases of the extreme values in some modes of operation (Section 10.7 “Modes of

Operation” on page 88).

Figure 10-3 shows a block diagram of the output compare unit.

Figure 10-3. Output Compare Unit, Block Diagram

The OCR0A register is double buffered when using any of the pulse width modulation (PWM) modes. For the normal and

clear timer on compare (CTC) modes of operation, the double buffering is disabled. The double buffering synchronizes the

update of the OCR0A compare register to either top or bottom of the counting sequence. The synchronization prevents the

occurrence of odd-length, non-symmetrical PWM pulses, thereby making the output glitch-free.

The OCR0A register access may seem complex, but this is not case. When the double buffering is enabled, the CPU has

access to the OCR0A buffer register, and if double buffering is disabled the CPU will access the OCR0A directly.

10.5.1 Force Output Compare

In non-PWM waveform generation modes, the match output of the comparator can be forced by writing a one to the force

output compare (FOC0A) bit. Forcing compare match will not set the OCF0A flag or reload/clear the timer, but the OC0A pin

will be updated as if a real compare match had occurred (the COM0A1:0 bits settings define whether the OC0A pin is set,

cleared or toggled).

10.5.2 Compare Match Blocking by TCNT0 Write

All CPU write operations to the TCNT0 register will block any compare match that occurs in the next timer clock cycle, even

when the timer is stopped. This feature allows OCR0A to be initialized to the same value as TCNT0 without triggering an

interrupt when the timer/counter clock is enabled.

OCFnx (Int. Req.)

= (8-bit Comparator)

OCRnx

Waveform Generator

TCNTn

OCnx

top

bottom

FOCn

WGMn1:0 COMnX1:0

DATA BUS

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10.5.3 Using the Output Compare Unit

Since writing TCNT0 in any mode of operation will block all compare matches for one timer clock cycle, there are risks

involved when changing TCNT0 when using the output compare channel, independently of whether the timer/counter is

running or not. If the value written to TCNT0 equals the OCR0A value, the compare match will be missed, resulting in

incorrect waveform generation. Similarly, do not write the TCNT0 value equal to BOTTOM when the counter is down

counting.

The setup of the OC0A should be performed before setting the data direction register for the port pin to output. The easiest

way of setting the OC0A value is to use the force output compare (FOC0A) strobe bit in normal mode. The OC0A register

keeps its value even when changing between waveform generation modes.

Be aware that the COM0A1:0 bits are not double buffered together with the compare value. Changing the COM0A1:0 bits

will take effect immediately.

10.6 Compare Match Output Unit

The compare output mode (COM0A1:0) bits have two functions. The waveform generator uses the COM0A1:0 bits for

defining the output compare (OC0A) state at the next compare match. Also, the COM0A1:0 bits control the OC0A pin output

source. Figure 10-4 shows a simplified schematic of the logic affected by the COM0A1:0 bit setting. The I/O Registers, I/O

bits, and I/O pins in the figure are shown in bold. Only the parts of the general I/O port control registers (DDR and PORT)

that are affected by the COM0A1:0 bits are shown. When referring to the OC0A state, the reference is for the internal OC0A

Figure 10-4. Compare Match Output Logic

10.6.1 Compare Output Function

The general I/O port function is overridden by the output compare (OC0A) from the waveform generator if either of the

COM0A1:0 bits are set. However, the OC0A pin direction (input or output) is still controlled by the data direction register

(DDR) for the port pin. The data direction register bit for the OC0A pin (DDR_OC0A) must be set as output before the OC0A

value is visible on the pin. The port override function is independent of the waveform generation mode.

The design of the output compare pin logic allows initialization of the OC0A state before the output is enabled. Note that

some COM0A1:0 bit settings are reserved for certain modes of operation. Section 10.11 “8-bit Timer/Counter Register

Description” on page 95

DATA BUS

COMnx1

COMnx0

FOCn

OCnx

Waveform

Generator

PORT

DDR

OCnx

clkI/O

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10.6.2 Compare Output Mode and Waveform Generation

The waveform generator uses the COM0A1:0 bits differently in normal, CTC, and PWM modes. For all modes, setting the

COM0A1:0 = 0 tells the waveform generator that no action on the OC0A register is to be performed on the next compare

match. For compare output actions in the non-PWM modes refer to Table 10-1 on page 96. For fast PWM mode, refer to

Table 10-2 on page 96, and for phase correct PWM refer to Table 10-3 on page 96.

A change of the COM0A1:0 bits state will have effect at the first compare match after the bits are written. For non-PWM

modes, the action can be forced to have immediate effect by using the FOC0A strobe bits.

10.7 Modes of Operation

The mode of operation, i.e., the behavior of the timer/counter and the output compare pins, is defined by the combination of

the waveform generation mode (WGM01:0) and compare output mode (COM0A1:0) bits. The compare output mode bits do

not affect the counting sequence, while the waveform generation mode bits do. The COM0A1:0 bits control whether the

PWM output generated should be inverted or not (inverted or non-inverted PWM). For non-PWM modes the COM0A1:0 bits

control whether the output should be set, cleared, or toggled at a compare match (Section 10.6 “Compare Match Output

Unit” on page 87).

For detailed timing information refer to Section 10.8 “Timer/Counter Timing Diagrams” on page 92.

10.7.1 Normal Mode

The simplest mode of operation is the normal mode (WGM01:0 = 0). In this mode the counting direction is always up

(incrementing), and no counter clear is performed. The counter simply overruns when it passes its maximum 8-bit value

(TOP = 0xFF) and then restarts from the bottom (0x00). In normal operation the timer/counter overflow flag (TOV0) will be

set in the same timer clock cycle as the TCNT0 becomes zero. The TOV0 flag in this case behaves like a ninth bit, except

that it is only set, not cleared. However, combined with the timer overflow interrupt that automatically clears the TOV0 flag,

the timer resolution can be increased by software. There are no special cases to consider in the normal mode, a new counter

value can be written anytime.

The output compare unit can be used to generate interrupts at some given time. Using the output compare to generate

waveforms in normal mode is not recommended, since this will occupy too much of the CPU time.

10.7.2 Clear Timer on Compare Match (CTC) Mode

In clear timer on compare or CTC mode (WGM01:0 = 2), the OCR0A register is used to manipulate the counter resolution. In

CTC mode the counter is cleared to zero when the counter value (TCNT0) matches the OCR0A. The OCR0A defines the top

value for the counter, hence also its resolution. This mode allows greater control of the compare match output frequency. It

also simplifies the operation of counting external events.

The timing diagram for the CTC mode is shown in Figure 10-5. The counter value (TCNT0) increases until a compare match

occurs between TCNT0 and OCR0A, and then counter (TCNT0) is cleared.

Figure 10-5. CTC Mode, Timing Diagram

TCNTn

(COMnx1:0 = 1)

OCnx

(Toggle)

Period 3

OCnx Interrupt

Flag Set

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An interrupt can be generated each time the counter value reaches the TOP value by using the OCF0A flag. If the interrupt

is enabled, the interrupt handler routine can be used for updating the TOP value. However, changing the TOP to a value

close to BOTTOM when the counter is running with none or a low prescaler value must be done with care since the CTC

mode does not have the double buffering feature. If the new value written to OCR0A is lower than the current value of

TCNT0, the counter will miss the compare match. The counter will then have to count to its maximum value (0xFF) and wrap

around starting at 0x00 before the compare match can occur.

For generating a waveform output in CTC mode, the OC0A output can be set to toggle its logical level on each compare

match by setting the compare output mode bits to toggle mode (COM0A1:0 = 1). The OC0A value will not be visible on the

port pin unless the data direction for the pin is set to output. The waveform generated will have a maximum frequency of

fOC0A = fclk_I/O/2 when OCR0A is set to zero (0x00). The waveform frequency is defined by the following equation:

The N variable represents the prescale factor (1, 8, 32, 64, 128, 256, or 1024).

As for the normal mode of operation, the TOV0 flag is set in the same timer clock cycle that the counter counts from MAX to

0x00.

10.7.3 Fast PWM Mode

The fast pulse width modulation or fast PWM mode (WGM01:0 = 3) provides a high frequency PWM waveform generation

option. The fast PWM differs from the other PWM option by its single-slope operation. The counter counts from BOTTOM to

MAX then restarts from BOTTOM. In non-inverting compare output mode, the output compare (OC0A) is cleared on the

compare match between TCNT0 and OCR0A, and set at BOTTOM. In inverting compare output mode, the output is set on

compare match and cleared at BOTTOM. Due to the single-slope operation, the operating frequency of the fast PWM mode

can be twice as high as the phase correct PWM mode that uses dual-slope operation. This high frequency makes the fast

PWM mode well suited for power regulation, rectification, and DAC applications. High frequency allows physically small

sized external components (coils, capacitors), and therefore reduces total system cost.

In fast PWM mode, the counter is incremented until the counter value matches the MAX value. The counter is then cleared

at the following timer clock cycle. The timing diagram for the fast PWM mode is shown in Figure 10-6. The TCNT0 value is in

the timing diagram shown as a histogram for illustrating the single-slope operation. The diagram includes non-inverted and

inverted PWM outputs. The small horizontal line marks on the TCNT0 slopes represent compare matches between OCR0A

and TCNT0.

Figure 10-6. Fast PWM Mode, Timing Diagram

The timer/counter overflow flag (TOV0) is set each time the counter reaches MAX. If the interrupt is enabled, the interrupt

handler routine can be used for updating the compare value.

fOCnx

fclk_I/O

2N1OCRnx+

-------------------------------------------------

1234567

TCNTn

(COMnx1:0 = 2)

(COMnx1:0 = 3)

OCnx

Period

OCRnx Update and

TOVn Interrupt Flag Set

OCRnx Interrupt

Flag Set

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In fast PWM mode, the compare unit allows generation of PWM waveforms on the OC0A pin. Setting the COM0A1:0 bits to

two will produce a non-inverted PWM and an inverted PWM output can be generated by setting the COM0A1:0 to three (See

Table 10-2 on page 96). The actual OC0A value will only be visible on the port pin if the data direction for the port pin is set

as output. The PWM waveform is generated by setting (or clearing) the OC0A register at the compare match between

OCR0A and TCNT0, and clearing (or setting) the OC0A register at the timer clock cycle the counter is cleared (changes from

MAX to BOTTOM).

The PWM frequency for the output can be calculated by the following equation:

The N variable represents the prescale factor (1, 8, 32, 64, 128, 256, or 1024).

The extreme values for the OCR0A register represent special cases when generating a PWM waveform output in the fast

PWM mode. If the OCR0A is set equal to BOTTOM, the output will be a narrow spike for each MAX+1 timer clock cycle.

Setting the OCR0A equal to MAX will result in a constantly high or low output (depending on the polarity of the output set by

the COM0A1:0 bits.)

A frequency (with 50% duty cycle) waveform output in fast PWM mode can be achieved by setting OC0A to toggle its logical

level on each compare match (COM0A1:0 = 1). The waveform generated will have a maximum frequency of foc0A = fclk_I/O/2

when OCR0A is set to zero. This feature is similar to the OC0A toggle in CTC mode, except the double buffer feature of the

output compare unit is enabled in the fast PWM mode.

10.7.4 Phase Correct PWM Mode

The phase correct PWM mode (WGM01:0 = 1) provides a high resolution phase correct PWM waveform generation option.

The phase correct PWM mode is based on a dual-slope operation. The counter counts repeatedly from BOTTOM to MAX

and then from MAX to BOTTOM. In non-inverting compare output mode, the output compare (OC0A) is cleared on the

compare match between TCNT0 and OCR0A while up counting, and set on the compare match while down counting. In

inverting output compare mode, the operation is inverted. The dual-slope operation has lower maximum operation frequency

than single slope operation. However, due to the symmetric feature of the dual-slope PWM modes, these modes are

preferred for motor control applications.

The PWM resolution for the phase correct PWM mode is fixed to eight bits. In phase correct PWM mode the counter is

incremented until the counter value matches MAX. When the counter reaches MAX, it changes the count direction. The

TCNT0 value will be equal to MAX for one timer clock cycle. The timing diagram for the phase correct PWM mode is shown

on Figure 10-7 on page 91. The TCNT0 value is in the timing diagram shown as a histogram for illustrating the dual-slope

operation. The diagram includes non-inverted and inverted PWM outputs. The small horizontal line marks on the TCNT0

slopes represent compare matches between OCR0A and TCNT0.

fOCnxPWM

fclk_I/O

N256

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Figure 10-7. Phase Correct PWM Mode, Timing Diagram

The timer/counter overflow flag (TOV0) is set each time the counter reaches BOTTOM. The interrupt flag can be used to

generate an interrupt each time the counter reaches the BOTTOM value.

In phase correct PWM mode, the compare unit allows generation of PWM waveforms on the OC0A pin. Setting the

COM0A1:0 bits to two will produce a non-inverted PWM. An inverted PWM output can be generated by setting the

COM0A1:0 to three (See Table 10-3 on page 96). The actual OC0A value will only be visible on the port pin if the data

direction for the port pin is set as output. The PWM waveform is generated by clearing (or setting) the OC0A Register at the

compare match between OCR0A and TCNT0 when the counter increments, and setting (or clearing) the OC0A register at

compare match between OCR0A and TCNT0 when the counter decrements. The PWM frequency for the output when using

phase correct PWM can be calculated by the following equation:

The N variable represents the prescale factor (1, 8, 32, 64, 128, 256, or 1024).

The extreme values for the OCR0A register represent special cases when generating a PWM waveform output in the phase

correct PWM mode. If the OCR0A is set equal to BOTTOM, the output will be continuously low and if set equal to MAX the

output will be continuously high for non-inverted PWM mode. For inverted PWM the output will have the opposite logic

values.

123

TCNTn

(COMnx1:0 = 2)

(COMnx1:0 = 3)

OCnx

Period

TOVn Interrupt

Flag Set

OCRnx Update

OCnx Interrupt

Flag Set

fOCnxPCPWM

fclk_I/O

N510

-----------------

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10.8 Timer/Counter Timing Diagrams

The following figures show the timer/counter in synchronous mode, and the timer clock (clkT0) is therefore shown as a clock

enable signal. In asynchronous mode, clkI/O should be replaced by the timer/counter oscillator clock. The figures include

information on when interrupt flags are set. Figure 10-8 contains timing data for basic timer/counter operation. The figure

shows the count sequence close to the MAX value in all modes other than phase correct PWM mode.

Figure 10-8. Timer/Counter Timing Diagram, no Prescaling

Figure 10-9 shows the same timing data, but with the prescaler enabled.

Figure 10-9. Timer/Counter Timing Diagram, with Prescaler (fclk_I/O/8)

Figure 10-10 shows the setting of OCF0A in all modes except CTC mode.

Figure 10-10.Timer/Counter Timing Diagram, Setting of OCF0A, with Prescaler (fclk_I/O/8)

MAX - 1

clkI/O

(clkI/O/1)

TCNTn

TOVn

clkTn

MAX BOTTOM BOTTOM + 1

MAX - 1

clkI/O

(clkI/O/8)

TCNTn

TOVn

clkTn

MAX BOTTOM BOTTOM + 1

OCRnx - 1

clkI/O

(clkI/O/8)

TCNTn

OCRnx

OCFnx

clkTn

OCRnx OCRnx + 1

OCRnx Value

OCRnx + 2

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Figure 10-11 shows the setting of OCF0A and the clearing of TCNT0 in CTC mode.

Figure 10-11.Timer/Counter Timing Diagram, Clear Timer on Compare Match mode, with Prescaler (fclk_I/O/8)

10.9 Asynchronous Operation of Timer/Counter0

When timer/counter0 operates asynchronously, some considerations must be taken.

Warning: When switching between asynchronous and synchronous clocking of timer/counter0, the timer registers

TCNT0, OCR0A, and TCCR0A might be corrupted. A safe procedure for switching clock source is:

1. Disable the timer/counter0 interrupts by clearing OCIE0A and TOIE0.

2. Select clock source by setting AS0 and EXCLK as appropriate.

3. Write new values to TCNT0, OCR0A, and TCCR0A.

4. To switch to asynchronous operation: wait for TCN0UB, OCR0UB, and TCR0UB.

5. Clear the timer/counter0 interrupt flags.

6. Enable interrupts, if needed.

●If an 32.768kHz watch crystal is used, the CPU main clock frequency must be more than four times the oscillator or

external clock frequency.

●When writing to one of the registers TCNT0, OCR0A, or TCCR0A, the value is transferred to a temporary register,

and latched after two positive edges on TOSC1. The user should not write a new value before the contents of the

temporary register have been transferred to its destination. Each of the three mentioned registers have their individual

temporary register, which means that e.g. writing to TCNT0 does not disturb an OCR0A write in progress. To detect

that a transfer to the destination register has taken place, the asynchronous status register – ASSR has been

implemented.

●When entering power-save mode after having written to TCNT0, OCR0A, or TCCR0A, the user must wait until the

written register has been updated if timer/counter0 is used to wake up the device. Otherwise, the MCU will enter sleep

mode before the changes are effective. This is particularly important if the output compare0 interrupt is used to wake

up the device, since the output compare function is disabled during writing to OCR0A or TCNT0. If the write cycle is

not finished, and the MCU enters sleep mode before the OCR0UB bit returns to zero, the device will never receive a

compare match interrupt, and the MCU will not wake up.

TOP - 1

clkI/O

(clkI/O/8)

TCNTn

(CTC)

OCRnx

OCFnx

clkTn

TOP BOTTOM

TOP

BOTTOM + 1

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●If timer/counter0 is used to wake the device up from power-save mode, precautions must be taken if the user wants to

re-enter one of these modes: The interrupt logic needs one TOSC1 cycle to be reset. If the time between wake-up

and re-entering sleep mode is less than one TOSC1 cycle, the interrupt will not occur, and the device will fail to wake

up. If the user is in doubt whether the time before re-entering power-save mode is sufficient, the following algorithm

can be used to ensure that one TOSC1 cycle has elapsed:

a. Write a value to TCCR0A, TCNT0, or OCR0A.

b. Wait until the corresponding update busy flag in ASSR returns to zero.

c. Enter power-save or ADC noise reduction mode.

●When the asynchronous operation is selected, the oscillator for timer/counter0 is always running, except in power-

down mode. After a power-up reset or wake-up from power-down mode, the user should be aware of the fact that this

oscillator might take as long as one second to stabilize. The user is advised to wait for at least one second before

using timer/counter0 after power-up or wake-up from power-down mode. The contents of all timer/counter0 registers

must be considered lost after a wake-up from power-down mode due to unstable clock signal upon start-up, no matter

whether the oscillator is in use or a clock signal is applied to the XTAL1 pin.

●Description of wake up from power-save mode when the timer is clocked asynchronously: When the interrupt

condition is met, the wake up process is started on the following cycle of the timer clock, that is, the timer is always

advanced by at least one before the processor can read the counter value. After wake-up, the MCU is halted for four

cycles, it executes the interrupt routine, and resumes execution from the instruction following SLEEP.

●Reading of the TCNT0 register shortly after wake-up from power-save may give an incorrect result. Since TCNT0 is

clocked on the asynchronous clock, reading TCNT0 must be done through a register synchronized to the internal I/O

clock domain (CPU main clock). Synchronization takes place for every rising XTAL1 edge. When waking up from

power-save mode, and the I/O clock (clkI/O) again becomes active, TCNT0 will read as the previous value (before

entering sleep) until the next rising XTAL1 edge. The phase of the XTAL1 clock after waking up from power-save

mode is essentially unpredictable, as it depends on the wake-up time. The recommended procedure for reading

TCNT0 is thus as follows:

a. Write any value to either of the registers OCR0A or TCCR0A.

b. Wait for the corresponding update busy flag to be cleared.

c. Read TCNT0.

●During asynchronous operation, the synchronization of the interrupt flags for the asynchronous timer takes

3 processor cycles plus one timer cycle. The timer is therefore advanced by at least one before the processor can

read the timer value causing the setting of the interrupt flag. The output compare pin is changed on the timer clock

and is not synchronized to the processor clock.

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10.10 Timer/Counter0 Prescaler

Figure 10-12.Prescaler for Timer/Counter0

The clock source for timer/counter0 is named clkT0S. clkT0S is by default connected to the main system I/O clock clkIO. By

setting the AS0 bit in ASSR, timer/counter0 is asynchronously clocked from the XTAL oscillator or XTAL1 pin. This enables

use of timer/counter0 as a real time counter (RTC).

A crystal can then be connected between the XTAL1 and XTAL2 pins to serve as an independent clock source for

timer/counter0.

A external clock can also be used using XTAL1 as input. Setting AS0 and EXCLK enables this configuration.

For timer/counter0, the possible prescaled selections are: clkT0S/8, clkT0S/32, clkT0S/64, clkT0S/128, clkT0S/256, and

clkT0S/1024. Additionally, clkT0S as well as 0 (stop) may be selected. Setting the PSR0 bit in GTCCR resets the prescaler.

This allows the user to operate with a predictable prescaler.

10.11 8-bit Timer/Counter Register Description

• Timer/Counter0 Control Register A – TCCR0A

• Bit 7:6 – COM0A1:0: Compare Match Output Mode A

These bits control the output compare pin (OC0A) behavior. If one or both of the COM0A1:0 bits are set, the OC0A output

overrides the normal port functionality of the I/O pin it is connected to. However, note that the data direction register (DDR)

bit corresponding to OC0A pin must be set in order to enable the output driver.

When OC0A is connected to the pin, the function of the COM0A1:0 bits depends on the WGM01:0 bit setting. Table 10-1 on

page 96 shows the COM0A1:0 bit functionality when the WGM01:0 bits are set to a normal or CTC mode (non-PWM).

Timer/Countern Clock Source

clkTn

clkTnS/8

clkTnS/32

clkTnS/64

clkTnS/128

clkTnS/256

clkTnS/1024

ASn

XTAL2

XTAL1

EXCLK

PSRn

clkTnS

clkI/O

10-bit T/C Prescaler

Clear

Oscillator

CSn0

CSn1

CSn2

Bit 7 6 5 4 3 210

COM0A1 COM0A0 – – – – WGM01 WGM00 TCCR0A

Read/Write R/W R/W R R R R R/W R/W

Initial Value 0 0 0 0 0 0 0 0

Note: 1. A special case occurs when OCROA equals TOP and COMO/M is set. In this case, the compare match is Note: 1. A special case occurs when OCROA equals TOP and COMO/M is set. In this case, the Compare Match is AtmeL

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Table 10-2 shows the COM0A1:0 bit functionality when the WGM01:0 bits are set to fast PWM mode.

Table 10-3 shows the COM01:0 bit functionality when the WGM01:0 bits are set to phase correct PWM mode

• Bit 5:2 – Res: Reserved Bits

These bits are reserved in the ATtiny87/167 and will always read as zero.

Table 10-1. Compare Output Mode, non-PWM Mode

COM0A1 COM0A0 Description

0 0 Normal port operation, OC0A disconnected.

0 1 Toggle OC0A on Compare Match.

1 0 Clear OC0A on Compare Match.

1 1 Set OC0A on Compare Match.

Table 10-2. Compare Output Mode, Fast PWM Mode(1)

COM0A1 COM0A0 Description

0 0 Normal port operation, OC0A disconnected.

0 1

1 0 Clear OC0A on compare match.

Set OC0A at BOTTOM (non-inverting mode).

1 1 Set OC0A on compare match.

Clear OC0A at BOTTOM (inverting mode).

Note: 1. A special case occurs when OCR0A equals TOP and COM0A1 is set. In this case, the compare match is

ignored, but the set or clear is done at TOP. See Section 10.7.3 “Fast PWM Mode” on page 89 for more

details.

Table 10-3. Compare Output Mode, Phase Correct PWM Mode(1)

COM0A1 COM0A0 Description

0 0 Normal port operation, OC0A disconnected.

0 1

1 0 Clear OC0A on compare match when up-counting.

Set OC0A on compare match when down-counting.

1 1 Set OC0A on compare match when up-counting.

Clear OC0A on compare match when down-counting.

Note: 1. A special case occurs when OCR0A equals TOP and COM0A1 is set. In this case, the Compare Match is

ignored, but the set or clear is done at TOP. See Section 10.7.4 “Phase Correct PWM Mode” on page 90 for

more details.

Notes: 1. MAX=0xFF, AtmeL

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Bit 6, 3 – WGM01:0: Waveform Generation Mode

These bits control the counting sequence of the counter, the source for the maximum (TOP) ccunter value, and what type of

waveform generation to be used, see Table 10-4. Modes of operation supported by the timer/Counter unit are: normal mode

(counter), clear timer on compare match (CTC) mode, and two types of pulse width modulation (PWM) modes (Section 10.7

“Modes of Operation” on page 88).

10.11.1 Timer/Counter0 Control Register B – TCCR0B

• Bit 7 – FOC0A: Force Output Compare A

The FOC0A bit is only active when the WGM bits specify a non-PWM mode.

However, for ensuring compatibility with future devices, this bit must be set to zero when TCCR0B is written when operating

in PWM mode. When writing a logical one to the FOC0A bit, an immediate compare match is forced on the waveform

generation unit. The OC0A output is changed according to its COM0A1:0 bits setting. Note that the FOC0A bit is

implemented as a strobe. Therefore it is the value present in the COM0A1:0 bits that determines the effect of the forced

compare.

A FOC0A strobe will not generate any interrupt, nor will it clear the timer in CTC mode using OCR0A as TOP.

The FOC0A bit is always read as zero.

• Bit 6:3 – Res: Reserved Bits

These bits are reserved in the Atmel® ATtiny87/167 and will always read as zero.

• Bit 2:0 – CS02:0: Clock Select

The three clock select bits select the clock source to be used by the timer/counter, see Table 10-5.

Table 10-4. Waveform Generation Mode Bit Description

Mode

WGM01

(CTC0)

WGM00

(PWM0)

Timer/Counter

Mode of Operation TOP

Update of

OCR0A at

TOV0 Flag

Set on(1)(2)

0 0 0 Normal 0xFF Immediate MAX

1 0 1 PWM, phase correct 0xFF TOP BOTTOM

2 1 0 CTC OCR0A Immediate MAX

3 1 1 Fast PWM 0xFF TOP MAX

Notes: 1. MAX = 0xFF,

2. BOTTOM = 0x00.

Bit 76 5 4 3 210

FOC0A – – – – CS02 CS01 CS00 TCCR0B

Read/Write W R R R R R/W R/W R/W

Initial Value 0 0 0 0 0 0 0 0

Table 10-5. Clock Select Bit Description

CS02 CS01 CS00 Description

0 0 0 No clock source (timer/counter stopped).

0 0 1 clkT0S (no prescaling)

0 1 0 clkT0S/8 (from prescaler)

0 1 1 clkT0S/32 (from prescaler)

1 0 0 clkT0S/64 (from prescaler)

1 0 1 clkT0S/128 (from prescaler)

1 1 0 clkT0S/256 (from prescaler)

1 1 1 clkT0S/1024 (from prescaler)

RIW RIW RM RM RIW RIW RIW 'le Fuw AtmeL

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10.11.2 Timer/Counter0 Register – TCNT0

The timer/counter register gives direct access, both for read and write operations, to the timer/counter unit 8-bit counter.

writing to the TCNT0 register blocks (removes) the compare match on the following timer clock. Modifying the counter

(TCNT0) while the counter is running, introduces a risk of missing a compare match between TCNT0 and the OCR0x

10.11.3 Output Compare Register A – OCR0A

The output compare register A contains an 8-bit value that is continuously compared with the counter value (TCNT0). A

match can be used to generate an output compare interrupt, or to generate a waveform output on the OC0A pin.

10.11.4 Asynchronous Status Register – ASSR

• Bit 7 – Res: Reserved Bit

This bit is reserved in the Atmel® ATtiny87/167 and will always read as zero.

• Bit 6 – EXCLK: Enable External Clock Input

When EXCLK is written to one, and asynchronous clock is selected, the external clock input buffer is enabled and an

external clock can be input on XTAL1 pin instead of an external crystal. Writing to EXCLK should be done before

asynchronous operation is selected. Note that the crystal oscillator will only run when this bit is zero.

• Bit 5 – AS0: Asynchronous Timer/Counter0

When AS0 is written to zero, timer/counter0 is clocked from the I/O clock, clkI/O and the timer/counter0 acts as a

synchronous peripheral.

When AS0 is written to one, timer/counter0 is clocked from the low-frequency crystal oscillator (see Section 4.2.5 “Low-

frequency Crystal Oscillator” on page 31) or from external clock on XTAL1 pin (see Section 4.2.6 “External Clock” on page

31) depending on EXCLK setting. When the value of AS0 is changed, the contents of TCNT0, OCR0A, and TCCR0A might

be corrupted.

AS0 also acts as a flag: timer/counter0 is clocked from the low-frequency crystal or from external clock ONLY IF the

calibrated internal RC oscillator or the internal watchdog oscillator is used to drive the system clock. After setting AS0, if the

switching is available, AS0 remains to 1, else it is forced to 0.

• Bit 4 – TCN0UB: Timer/Counter0 Update Busy

When timer/counter0 operates asynchronously and TCNT0 is written, this bit becomes set. When TCNT0 has been updated

from the temporary storage register, this bit is cleared by hardware. A logical zero in this bit indicates that TCNT0 is ready to

be updated with a new value.

Bit 76543210

TCNT07 TCNT06 TCNT05 TCNT04 TCNT03 TCNT02 TCNT01 TCNT00 TCNT0

Read/Write R/W R/W R/W R/W R/W R/W R/W R/W

Initial Value00000000

Bit 76543210

OCR0A7 OCR0A6 OCR0A5 OCR0A4 OCR0A3 OCR0A2 OCR0A1 OCR0A0 OCR0A

Read/Write R/W R/W R/W R/W R/W R/W R/W R/W

Initial Value00000000

Bit 7654 321 0

– EXCLK AS0 TCN0UB OCR0AUB – TCR0AUB TCR0BUB ASSR

Read/Write R R/W R/W R R R R R

Initial Value 0 0 0 0 0 0 0 0

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• Bit 3 – OCR0AUB: Output Compare 0 Register A Update Busy

When timer/counter0 operates asynchronously and OCR0A is written, this bit becomes set. When OCR0A has been

updated from the temporary storage register, this bit is cleared by hardware. A logical zero in this bit indicates that OCR0A is

ready to be updated with a new value.

• Bit 2 – Res: Reserved Bit

This bit is reserved in the Atmel® ATtiny87/167 and will always read as zero.

• Bit 1 – TCR0AUB: Timer/Counter0 Control Register A Update Busy

When timer/counter0 operates asynchronously and TCCR0A is written, this bit becomes set. When TCCR0A has been

updated from the temporary storage register, this bit is cleared by hardware. A logical zero in this bit indicates that TCCR0A

is ready to be updated with a new value.

• Bit 0 – TCR0BUB: Timer/Counter0 Control Register B Update Busy

When timer/counter0 operates asynchronously and TCCR0B is written, this bit becomes set. When TCCR0B has been

updated from the temporary storage register, this bit is cleared by hardware. A logical zero in this bit indicates that TCCR0B

is ready to be updated with a new value.

If a write is performed to any of the four timer/counter0 registers while its update busy flag is set, the updated value might get

corrupted and cause an unintentional interrupt to occur.

The mechanisms for reading TCNT0, OCR0A, TCCR0A and TCCR0B are different. When reading TCNT0, the actual timer

value is read. When reading OCR0A, TCCR0A or TCCR0B the value in the temporary storage register is read.

10.11.5 Timer/Counter0 Interrupt Mask Register – TIMSK0

• Bit 7:2 – Res: Reserved Bits

These bits are reserved in the Atmel ATtiny87/167 and will always read as zero.

• Bit 1 – OCIE0A: Timer/Counter0 Output Compare Match A Interrupt Enable

When the OCIE0A bit is written to one and the I-bit in the status register is set (one), the timer/counter0 compare match A

interrupt is enabled. The corresponding interrupt is executed if a compare match in timer/counter0 occurs, i.e., when the

OCF0A bit is set in the timer/counter0 interrupt flag register – TIFR0.

• Bit 0 – TOIE0: Timer/Counter0 Overflow Interrupt Enable

When the TOIE0 bit is written to one and the I-bit in the status register is set (one), the timer/counter0 overflow interrupt is

enabled. The corresponding interrupt is executed if an overflow in timer/counter0 occurs, i.e., when the TOV0 bit is set in the

timer/counter0 interrupt flag register – TIFR0.

10.11.6 Timer/Counter0 Interrupt Flag Register – TIFR0

• Bit 7:2 – Res: Reserved Bits

These bits are reserved in the Atmel ATtiny87/167 and will always read as zero.

Bit 76543210

––––––OCIE0ATOIE0TIMSK0

Read/Write RRRRRRR/WR/W

Initial Value00000000

Bit 76543210

––––––OCF0ATOV0TIFR0

Read/Write R R R R R R R/W R/W

Initial Value00000000

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100

Bit 1 – OCF0A: Output Compare Flag 0 A

The OCF0A bit is set (one) when a compare match occurs between the timer/counter0 and the data in OCR0A – output

Compare Register0. OCF0A is cleared by hardware when executing the corresponding interrupt handling vector.

alternatively, OCF0A is cleared by writing a logic one to the flag. When the I-bit in SREG, OCIE0 (timer/counter0 compare

match interrupt enable), and OCF0A are set (one), the timer/counter0 compare match interrupt is executed.

• Bit 0 – TOV0: Timer/Counter0 Overflow Flag

The TOV0 bit is set (one) when an overflow occurs in timer/counter0. TOV0 is cleared by hardware when executing the

corresponding interrupt handling vector. Alternatively, TOV0 is cleared by writing a logic one to the flag. When the SREG I-

bit, TOIE0A (timer/counter0 overflow interrupt enable), and TOV0 are set (one), the timer/counter0 overflow interrupt is

executed. In PWM mode, this bit is set when timer/counter0 changes counting direction at 0x00.

10.11.7 General Timer/Counter Control Register – GTCCR

• Bit 1 – PSR0: Prescaler Reset Timer/Counter0

When this bit is one, the timer/counter0 prescaler will be reset. This bit is normally cleared immediately by hardware. If the bit

is written when timer/counter0 is operating in asynchronous mode, the bit will remain one until the prescaler has been reset.

The bit will not be cleared by hardware if the TSM bit is set. Refer to the description of the Section • “Bit 7 – TSM:

Timer/Counter Synchronization Mode” on page 102 for a description of the timer/counter synchronization mode.

Bit 7 6 5 4 3 2 1 0

TSM – – – – – PSR0 PSR1 GTCCR

Read/Write R/W R R R R R R/W R/W

Initial Value 0 0 0 0 0 0 0 0

----------------------------- ___________________________ AtmeL

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11. Timer/Counter1 Prescaler

11.1 Overview

Most bit references in this section are written in general form. A lower case “n” replaces the timer/counter number.

11.1.1 Internal Clock Source

The timer/counter can be clocked directly by the system clock (by setting the CSn2:0 = 1). This provides the fastest

operation, with a maximum timer/counter clock frequency equal to system clock frequency (fCLK_I/O). Alternatively, one of

four taps from the prescaler can be used as a clock source. The prescaled clock has a frequency of either fCLK_I/O/8,

fCLK_I/O/64, fCLK_I/O/256, or fCLK_I/O/1024.

11.1.2 Prescaler Reset

The prescaler is free running, i.e., operates independently of the clock select logic of the timer/counter. Since the prescaler is

not affected by the timer/counter’s clock select, the state of the prescaler will have implications for situations where a

prescaled clock is used. One example of prescaling artifacts occurs when the timer is enabled and clocked by the prescaler

(6 > CSn2:0 >1). The number of system clock cycles from when the timer is enabled to the first count occurs can be from 1

to N+1 system clock cycles, where N equals the prescaler divisor (8, 64, 256, or 1024).

It is possible to use the prescaler reset for synchronizing the timer/counter to program execution. However, care must be

taken if the other timer/counter that shares the same prescaler also uses prescaling. A prescaler reset will affect the

prescaler period for all timer/counters it is connected to.

11.1.3 External Clock Source

An external clock source applied to the T1 pin can be used as timer/counter clock (clkT1). The T1 pin is sampled once every

system clock cycle by the pin synchronization logic. The synchronized (sampled) signal is then passed through the edge

detector. Figure 11-1 shows a functional equivalent block diagram of the T1 synchronization and edge detector logic. The

registers are clocked at the positive edge of the internal system clock (clkI/O). The latch is transparent in the high period of

the internal system clock.

The edge detector generates one clkT1 pulse for each positive (CSn2:0 =7) or negative (CSn2:0 = 6) edge it detects.

Figure 11-1. T1 Pin Sampling

The synchronization and edge detector logic introduces a delay of 2.5 to 3.5 system clock cycles from an edge has been

applied to the T1 pin to the counter is updated.

Enabling and disabling of the clock input must be done when T1 has been stable for at least one system clock cycle,

otherwise it is a risk that a false timer/counter clock pulse is generated.

Each half period of the external clock applied must be longer than one system clock cycle to ensure correct sampling. The

external clock must be guaranteed to have less than half the system clock frequency (fExtClk < fclk_I/O/2) given a 50/50 %

duty cycle. Since the edge detector uses sampling, the maximum frequency of an external clock it can detect is half the

sampling frequency (nyquist sampling theorem). However, due to variation of the system clock frequency and duty cycle

caused by oscillator source (crystal, resonator, and capacitors) tolerances, it is recommended that maximum frequency of an

external clock source is less than fclk_I/O/2.5.

An external clock source can not be prescaled.

Synchronization Edge Detector

Tn_sync

(to Clock

Select Logic)

D QD QD

clkI/O

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Figure 11-2. Prescaler for Timer/Counter(1)

Note: 1. The synchronization logic on the input pin (T1) is shown in Figure 11-1 on page 101.

11.2 Timer/Counter1 Prescalers Register Description

11.2.1 General Timer/Counter Control Register – GTCCR

• Bit 7 – TSM: Timer/Counter Synchronization Mode

Writing the TSM bit to one activates the timer/counter synchronization mode. In this mode, the value that is written to the

PSR0 and PSR1 bits is kept, hence keeping the corresponding prescaler reset signals asserted. This ensures that the

corresponding timer/counters are halted and can be configured to the same value without the risk of one of them advancing

during configuration. When the TSM bit is written to zero, the PSR0 and PSR1 bits are cleared by hardware, and the

timer/counters start counting simultaneously.

• Bit 0 – PSR1: Prescaler Reset Timer/Counter1

When this bit is one, timer/counter1 prescaler will be reset. This bit is normally cleared immediately by hardware, except if

the TSM bit is set.

clkTn

Timer/Counter n Clock Source

clkI/O

PSRn

10-bit T/C Prescaler

CSn0

CK/8

CK/64

CK/256

CK/1024

CSn1

CSn2

Synchronization

Clear

Bit 7 6 5 4 3 2 1 0

TSM – – – – – PSR0 PSR1 GTCCR

Read/Write R R R R R R R/W R/W

Initial Value 0 0 0 0 0 0 0 0

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12. 16-bit Timer/Counter1

The 16-bit timer/counter unit allows accurate program execution timing (event management), wave generation, and signal

timing measurement. The main features are:

12.1 Features

●True 16-bit design (i.e., Allows 16-bit PWM)

●Two independent output compare units

●Four controlled output pins per output compare unit

●Double buffered output compare registers

●One input capture unit

●Input capture noise canceler

●Clear timer on compare match (auto reload)

●Glitch-free, phase correct pulse width modulator (PWM)

●Variable PWM period

●Frequency generator

●External event counter

●Four independent interrupt sources (TOV1, OCF1A, OCF1B, and ICF1)

12.2 Overview

Many register and bit references in this section are written in general form.

●A lower case “n” replaces the timer/counter number, in this case 1. However, when using the register or bit defines in

a program, the precise form must be used, i.e., TCNT1 for accessing timer/counter1 counter value and so on.

●A lower case “x” replaces the output compare unit channel, in this case A or B. However, when using the register or bit

defines in a program, the precise form must be used, i.e., OCR1A for accessing timer/counter1 output compare

channel A value and so on.

●A lower case “i” replaces the index of the output compare output pin, in this case U, V, W or X. However, when using

the register or bit defines in a program, the precise form must be used.

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A simplified block diagram of the 16-bit timer/counter is shown in Figure 12-1. For the actual placement of I/O pins, refer to

Section 1.6 “Pin Configuration” on page 6. CPU accessible I/O Registers, including I/O bits and I/O pins, are shown in bold.

The device-specific I/O Register and bit locations are listed in the Section 12.11 “16-bit Timer/Counter Register Description”

on page 124.

Figure 12-1. 16-bit Timer/Counter1 Block Diagram(1)

Note: 1. Refer to Figure 1-2 on page 6, Table 9-6 on page 78, and Table 9-3 on page 73 for timer/counter1 pin place-

ment and description.

Control Logic

TCNTn

Timer/Counter

Count

Clear

Direction

clkTn

OCRnA

OCRnB

TCCRnA

ICRn

TCCRnB TCCRnC

Edge

Detector

(from Prescaler)

Clock Select

TOP BOTTOM

TOVn (Int. Req.)

OCFnA (Int. Req.)

Waveform

Generation

Fixed

TOP

Values

DATA BUS

== 0

OCnAU

OCnAV

OCnAW

OCnAX

OCFnB (Int. Req.)

Waveform

Generation

Noise

Canceler

OCnBU

(From Analog

Comparator Output)

OCnBV

OCnBW

OCnBX

ICFn (Int. Req.)

Edge

Detector ICPn

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12.2.1 Registers

The timer/counter (TCNT1), output compare registers (OCR1A/B), and input capture register (ICR1) are all 16-bit registers.

Special procedures must be followed when accessing the 16-bit registers. These procedures are described in the section

Section 12.3 “Accessing 16-bit Registers” on page 105. The timer/counter control registers (TCCR1A/B) are 8-bit registers

and have no CPU access restrictions. Interrupt requests (abbreviated to Int.Req. in the figure) signals are all visible in the

timer interrupt flag register (TIFR1). All interrupts are individually masked with the timer interrupt mask register (TIMSK1).

TIFR1 and TIMSK1 are not shown in the figure.

The timer/counter can be clocked internally, via the prescaler, or by an external clock source on the Tn pin. The clock select

logic block controls which clock source and edge the timer/counter uses to increment (or decrement) its value. The

timer/counter is inactive when no clock source is selected. The output from the clock select logic is referred to as the timer

clock (clkTn).

The double buffered output compare registers (OCR1A/B) are compared with the timer/counter value at all time. The result

of the compare can be used by the waveform generator to generate a PWM or variable frequency output on the output

compare pins, see Section 12.7 “Output Compare Units” on page 111. The compare match event will also set the compare

match flag (OCF1A/B) which can be used to generate an output compare interrupt request.

The input capture register can capture the timer/counter value at a given external (edge triggered) event on either the input

capture pin (ICP1) or on the analog comparator pins (see Section 18. “AnaComp - Analog Comparator” on page 194). The

input capture unit includes a digital filtering unit (noise canceler) for reducing the chance of capturing noise spikes.

The TOP value, or maximum timer/counter value, can in some modes of operation be defined by either the OCR1A register,

the ICR1 register, or by a set of fixed values. When using OCR1A as TOP value in a PWM mode, the OCR1A register can

not be used for generating a PWM output. However, the TOP value will in this case be double buffered allowing the TOP

value to be changed in run time. If a fixed TOP value is required, the ICR1 register can be used as an alternative, freeing the

OCR1A to be used as PWM output.

12.2.2 Definitions

The following definitions are used extensively throughout the section:

●BOTTOM: The counter reaches the BOTTOM when it becomes 0x0000.

●MAX: The counter reaches its MAXimum when it becomes 0xFFFF (decimal 65,535).

●TOP: The counter reaches the TOP when it becomes equal to the highest value in the count sequence. The TOP

value can be assigned to be one of the fixed values: 0x00FF, 0x01FF, or 0x03FF, or to the value stored in the OCR1A

or ICR1 register. The assignment is dependent of the mode of operation.

12.3 Accessing 16-bit Registers

The TCNT1, OCR1A/B, and ICR1 are 16-bit registers that can be accessed by the AVR® CPU via the 8-bit data bus. The

16-bit register must be byte accessed using two read or write operations. Each 16-bit timer has a single 8-bit register for

temporary storing of the high byte of the 16-bit access. The same temporary register is shared between all 16-bit registers

within each 16-bit timer. Accessing the low byte triggers the 16-bit read or write operation. When the low byte of a 16-bit

register is written by the CPU, the high byte stored in the temporary register, and the low byte written are both copied into the

16-bit register in the same clock cycle. When the low byte of a 16-bit register is read by the CPU, the high byte of the 16-bit

Not all 16-bit accesses uses the temporary register for the high byte. Reading the OCR1A/B 16-bit registers does not involve

using the temporary register.

To do a 16-bit write, the high byte must be written before the low byte. For a 16-bit read, the low byte must be read before the

high byte.

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12.3.1 Code Examples

The following code examples show how to access the 16-bit timer registers assuming that no interrupts updates the

temporary register. The same principle can be used directly for accessing the OCR1A/B and ICR1 registers. Note that when

using “C”, the compiler handles the 16-bit access.

Note: 1. The example code assumes that the part specific header file is included.

The assembly code example returns the TCNT1 value in the r17:r16 register pair.

It is important to notice that accessing 16-bit registers are atomic operations. If an interrupt occurs between the two

instructions accessing the 16-bit register, and the interrupt code updates the temporary register by accessing the same or

any other of the 16-bit timer registers, then the result of the access outside the interrupt will be corrupted. Therefore, when

both the main code and the interrupt code update the temporary register, the main code must disable the interrupts during

the 16-bit access.

Assembly Code Examples(1)

...

; Set TCNT1 to 0x01FF

ldi r17,0x01

ldi r16,0xFF

sts TCNT1H,r17

sts TCNT1L,r16

; Read TCNT1 into r17:r16

lds r16,TCNT1L

lds r17,TCNT1H

...

C Code Examples(1)

unsigned int i;

...

/* Set TCNT1 to 0x01FF */

TCNT1 = 0x1FF;

/* Read TCNT1 into i */

i = TCNT1;

...

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The following code examples show how to do an atomic read of the TCNT1 register contents. Reading any of the OCR1A/B

or ICR1 registers can be done by using the same principle.

Note: 1. The example code assumes that the part specific header file is included.

The assembly code example returns the TCNT1 value in the r17:r16 register pair.

Assembly Code Example(1)

TIM16_ReadTCNT1:

; Save global interrupt flag

in r18,SREG

; Disable interrupts

cli

; Read TCNT1 into r17:r16

lds r16,TCNT1L

lds r17,TCNT1H

; Restore global interrupt flag

out SREG,r18

ret

C Code Example(1)

unsigned int TIM16_ReadTCNT1(void)

{

unsigned char sreg;

unsigned int i;

/* Save global interrupt flag */

sreg = SREG;

/* Disable interrupts */

_CLI();

/* Read TCNT1 into i */

i = TCNT1;

/* Restore global interrupt flag */

SREG = sreg;

return i;

}

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The following code examples show how to do an atomic write of the TCNT1 register contents. Writing any of the OCR1A/B

or ICR1 registers can be done by using the same principle.

Note: 1. The example code assumes that the part specific header file is included.

The assembly code example requires that the r17:r16 register pair contains the value to be written to TCNT1.

12.3.2 Reusing the Temporary High Byte Register

If writing to more than one 16-bit register where the high byte is the same for all registers written, then the high byte only

needs to be written once. However, note that the same rule of atomic operation described previously also applies in this

case.

12.4 Timer/Counter Clock Sources

The Timer/Counter can be clocked by an internal or an external clock source. The clock source is selected by the Clock

Select logic which is controlled by the Clock Select (CS12:0) bits located in the Timer/Counter control Register B (TCCR1B).

For details on clock sources and prescaler, see Section 11. “Timer/Counter1 Prescaler” on page 101.

Assembly Code Example(1)

TIM16_WriteTCNT1:

; Save global interrupt flag

in r18,SREG

; Disable interrupts

cli

; Set TCNT1 to r17:r16

sts TCNT1H,r17

sts TCNT1L,r16

; Restore global interrupt flag

out SREG,r18

ret

C Code Example(1)

void TIM16_WriteTCNT1(unsigned int i)

{

unsigned char sreg;

unsigned int i;

/* Save global interrupt flag */

sreg = SREG;

/* Disable interrupts */

_CLI();

/* Set TCNT1 to i */

TCNT1 = i;

/* Restore global interrupt flag */

SREG = sreg;

}

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12.5 Counter Unit

The main part of the 16-bit timer/counter is the programmable 16-bit bi-directional counter unit. Figure 12-2 shows a block

diagram of the counter and its surroundings.

Figure 12-2. Counter Unit Block Diagram

Signal description (internal signals):

Count Increment or decrement TCNT1 by 1.

Direction Select between increment and decrement.

Clear Clear TCNT1 (set all bits to zero).

clkT1 Timer/counter clock.

TOP Signalize that TCNT1 has reached maximum value.

BOTTOM Signalize that TCNT1 has reached minimum value (zero).

The 16-bit counter is mapped into two 8-bit I/O memory locations: counter High (TCNT1H) containing the upper eight bits of

the counter, and counter low (TCNT1L) containing the lower eight bits. The TCNT1H register can only be indirectly accessed

by the CPU. When the CPU does an access to the TCNT1H I/O location, the CPU accesses the high byte temporary register

(TEMP). The temporary register is updated with the TCNT1H value when the TCNT1L is read, and TCNT1H is updated with

the temporary register value when TCNT1L is written. This allows the CPU to read or write the entire 16-bit counter value

within one clock cycle via the 8-bit data bus. It is important to notice that there are special cases of writing to the TCNT1

register when the counter is counting that will give unpredictable results. The special cases are described in the sections

where they are of importance.

Depending on the mode of operation used, the counter is cleared, incremented, or decremented at each timer clock (clkT1).

The clkT1 can be generated from an external or internal clock source, selected by the clock select bits (CS12:0). When no

clock source is selected (CS12:0 = 0) the timer is stopped. However, the TCNT1 value can be accessed by the CPU,

independent of whether clkT1 is present or not. A CPU write overrides (has priority over) all counter clear or count

operations.

The counting sequence is determined by the setting of the waveform generation mode bits (WGM13:0) located in the

timer/counter control registers A and B (TCCR1A and TCCR1B). There are close connections between how the counter

behaves (counts) and how waveforms are generated on the output compare outputs OC1A/B. For more details about

advanced counting sequences and waveform generation, see Section 12.9 “Modes of Operation” on page 115.

The timer/counter overflow flag (TOV1) is set according to the mode of operation selected by the WGM13:0 bits. TOV1 can

be used for generating a CPU interrupt.

BOTTOMTOP

TOVn

(Int. Req.)

DATA BUS (8-bit)

Control Logic

TCNTnH (8-bit)

TCNTn (16-bit Counter)

TCNTnL (8-bit)

TEMP (8-bit)

clkTn

Clear

Count

Direction

Edge

Detector

(from Prescaler)

Clock Select

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12.6 Input Capture Unit

The timer/counter incorporates an input capture unit that can capture external events and give them a time-stamp indicating

time of occurrence. The external signal indicating an event, or multiple events, can be applied via the ICP1 pin or

alternatively, via the analog-comparator unit. The time-stamps can then be used to calculate frequency, duty-cycle, and

other features of the signal applied. Alternatively the time-stamps can be used for creating a log of the events.

The input capture unit is illustrated by the block diagram shown in Figure 12-3. The elements of the block diagram that are

not directly a part of the input capture unit are gray shaded.

Figure 12-3. Input Capture Unit Block Diagram

When a change of the logic level (an event) occurs on the input capture pin (ICP1), alternatively on the analog comparator

output (ACO), and this change confirms to the setting of the edge detector, a capture will be triggered. When a capture is

triggered, the 16-bit value of the counter (TCNT1) is written to the input capture register (ICR1). The input capture flag (ICF1)

is set at the same system clock as the TCNT1 value is copied into ICR1 register. If enabled (ICIE1 = 1), the input capture flag

generates an input capture interrupt. The ICF1 flag is automatically cleared when the interrupt is executed. Alternatively the

ICF1 flag can be cleared by software by writing a logical one to its I/O bit location.

Reading the 16-bit value in the input capture register (ICR1) is done by first reading the low byte (ICR1L) and then the high

byte (ICR1H). When the low byte is read the high byte is copied into the high byte temporary register (TEMP). When the

CPU reads the ICR1H I/O location it will access the TEMP register.

The ICR1 register can only be written when using a waveform generation mode that utilizes the ICR1 register for defining the

counter’s TOP value. In these cases the waveform generation mode (WGM13:0) bits must be set before the TOP value can

be written to the ICR1 register. When writing the ICR1 register the high byte must be written to the ICR1H I/O location before

the low byte is written to ICR1L.

For more information on how to access the 16-bit registers refer to Section 12.3 “Accessing 16-bit Registers” on page 105.

ICF1n (Int. Req.)

ICRnL (8-bit)ICRnH (8-bit)

ICRn (16-bit Register)

TEMP (8-bit)

TCNTnL (8-bit)TCNTnH (8-bit)

TCNTn (16-bit Counter)

DATA BUS (8-bit)

Noise

Canceler

Analog

Comparator

Edge

Detector

ICNCnACIC

ACO

WRITE

ICESn

ICPn

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12.6.1 Input Capture Trigger Source

The main trigger source for the input capture unit is the input capture pin (ICP1). Only timer/counter1 can alternatively use

the analog comparator output as trigger source for the input capture unit. The analog comparator is selected as trigger

source by setting the Analog Comparator Input Capture (ACIC) bit in the analog comparator control and status register

(ACSR). Be aware that changing trigger source can trigger a capture. The input capture flag must therefore be cleared after

the change.

Both the input capture pin (ICP1) and the analog comparator output (ACO) inputs are sampled using the same technique as

for the T1 pin (Figure 11-1 on page 101). The edge detector is also identical. However, when the noise canceler is enabled,

additional logic is inserted before the edge detector, which increases the delay by four system clock cycles. Note that the

input of the noise canceler and edge detector is always enabled unless the timer/counter is set in a waveform generation

mode that uses ICR1 to define TOP.

An input capture can be triggered by software by controlling the port of the ICP1 pin.

12.6.2 Noise Canceler

The noise canceler improves noise immunity by using a simple digital filtering scheme. The noise canceler input is monitored

over four samples, and all four must be equal for changing the output that in turn is used by the edge detector.

The noise canceler is enabled by setting the input capture noise canceler (ICNC1) bit in timer/counter control register B

(TCCR1B). When enabled the noise canceler introduces additional four system clock cycles of delay from a change applied

to the input, to the update of the ICR1 register. The noise canceler uses the system clock and is therefore not affected by the

prescaler.

12.6.3 Using the Input Capture Unit

The main challenge when using the input capture unit is to assign enough processor capacity for handling the incoming

events. The time between two events is critical. If the processor has not read the captured value in the ICR1 register before

the next event occurs, the ICR1 will be overwritten with a new value. In this case the result of the capture will be incorrect.

When using the input capture interrupt, the ICR1 register should be read as early in the interrupt handler routine as possible.

Even though the input capture interrupt has relatively high priority, the maximum interrupt response time is dependent on the

maximum number of clock cycles it takes to handle any of the other interrupt requests.

Using the input capture unit in any mode of operation when the TOP value (resolution) is actively changed during operation,

is not recommended.

Measurement of an external signal’s duty cycle requires that the trigger edge is changed after each capture. Changing the

edge sensing must be done as early as possible after the ICR1 register has been read. After a change of the edge, the input

capture flag (ICF1) must be cleared by software (writing a logical one to the I/O bit location). For measuring frequency only,

the clearing of the ICF1 flag is not required (if an interrupt handler is used).

12.7 Output Compare Units

The 16-bit comparator continuously compares TCNT1 with the output compare register (OCR1A/B). If TCNT equals

OCR1A/B the comparator signals a match. A match will set the output compare flag (OCF1A/B) at the next timer clock cycle.

If enabled (OCIE1A/B = 1), the output compare flag generates an output compare interrupt. The OCF1A/B flag is

automatically cleared when the interrupt is executed. Alternatively the OCF1A/B flag can be cleared by software by writing a

logical one to its I/O bit locations. The waveform generator uses the match signal to generate an output according to

operating mode set by the waveform generation mode (WGM13:0) bits and compare output mode (COM1A/B1:0) bits. The

TOP and BOTTOM signals are used by the waveform generator for handling the special cases of the extreme values in

some modes of operation (see Section 12.9 “Modes of Operation” on page 115)

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A special feature of output compare unit A allows it to define the timer/counter TOP value (i.e., counter resolution). In

addition to the counter resolution, the TOP value defines the period time for waveforms generated by the waveform

generator.

Figure 12-4 shows a block diagram of the output compare unit. The elements of the block diagram that are not directly a part

of the output compare unit are gray shaded.

Figure 12-4. Output Compare Unit, Block Diagram

The OCR1A/B register is double buffered when using any of the twelve pulse width modulation (PWM) modes. For the

normal and clear timer on compare (CTC) modes of operation, the double buffering is disabled. The double buffering

synchronizes the update of the OCR1A/B compare register to either TOP or BOTTOM of the counting sequence. The

synchronization prevents the occurrence of odd-length, non-symmetrical PWM pulses, thereby making the output glitch-free.

The OCR1A/B register access may seem complex, but this is not case. When the double buffering is enabled, the CPU has

access to the OCR1A/B buffer register, and if double buffering is disabled the CPU will access the OCR1A/B directly. The

content of the OCR1A/B (buffer or compare) register is only changed by a write operation (the timer/counter does not update

this register automatically as the TCNT1 and ICR1 register). Therefore OCR1A/B is not read via the high byte temporary

register (TEMP). However, it is a good practice to read the low byte first as when accessing other 16-bit registers. Writing the

OCR1A/B registers must be done via the TEMP register since the compare of all 16 bits is done continuously. The high byte

(OCR1A/BH) has to be written first. When the high byte I/O location is written by the CPU, the TEMP register will be updated

by the value written. Then when the low byte (OCR1A/BL) is written to the lower eight bits, the high byte will be copied into

the upper 8-bits of either the OCR1A/B buffer or OCR1A/B compare register in the same system clock cycle.

For more information of how to access the 16-bit registers refer to Section 12.3 “Accessing 16-bit Registers” on page 105.

OCRnxL Buf. (8-bit)OCRnxH Buf. (8-bit)

OCRnx Buffer (16-bit Register)

TEMP (8-bit)

OCRnxL (8-bit)

OCFnx (Int. Req.)

OCRnxH (8-bit)

OCRnx (16-bit Register)

(16-bitComparator)

WGMn3:0 COMnx1:0

Waveform Generator

TCNTnL (8-bit)TCNTnH (8-bit)

TCNTn (16-bit Counter)

DATA BUS (8-bit)

OCnxV

TOP

BOTTOM

OCnxU

OCnxX

OCnxW

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12.7.1 Force Output Compare

In non-PWM waveform generation modes, the match output of the comparator can be forced by writing a one to the force

output compare (FOC1A/B) bit. Forcing compare match will not set the OCF1A/B flag or reload/clear the timer, but the

OC1A/Bi pins will be updated as if a real compare match had occurred (the COM1A/B1:0 bits settings define whether the

OC1A/Bi pins are set, cleared or toggled - if the respective OCnxi bit is set).

12.7.2 Compare Match Blocking by TCNT1 Write

All CPU writes to the TCNT1 register will block any compare match that occurs in the next timer clock cycle, even when the

timer is stopped. This feature allows OCR1A/B to be initialized to the same value as TCNT1 without triggering an interrupt

when the timer/counter clock is enabled.

12.7.3 Using the Output Compare Unit

Since writing TCNT1 in any mode of operation will block all compare matches for one timer clock cycle, there are risks

involved when changing TCNT1 when using any of the output compare channels, independent of whether the timer/counter

is running or not. If the value written to TCNT1 equals the OCR1A/B value, the compare match will be missed, resulting in

incorrect waveform generation. Do not write the TCNT1 equal to TOP in PWM modes with variable TOP values. The

compare match for the TOP will be ignored and the counter will continue to 0xFFFF. Similarly, do not write the TCNT1 value

equal to BOTTOM when the counter is down counting.

The setup of the OC1A/B should be performed before setting the data direction register for the port pin to output. The easiest

way of setting the OC1A/B value is to use the force output compare (FOC1A/B) strobe bits in normal mode. The OC1A/B

Be aware that the COM1A/B1:0 bits are not double buffered together with the compare value. Changing the COM1A/B1:0

bits will take effect immediately.

12.8 Compare Match Output Unit

The compare output mode (COM1A/B1:0) bits have two functions. The waveform generator uses the COM1A/B1:0 bits for

defining the output compare (OC1A/B) state at the next compare match. Secondly the COM1A/B1:0 and OCnxi bits control

the OC1A/Bi pin output source. Figure 12-6 on page 115 shows a simplified schematic of the logic affected by the

COM1A/B1:0 and OCnxi bit setting. The I/O registers, I/O bits, and I/O pins in the figure are shown in bold. Only the parts of

the general I/O port control registers (DDR and PORT) that are affected by the COM1A/B1:0 and OCnxi bits are shown.

When referring to the OC1A/B state, the reference is for the internal OC1A/B register, not the OC1A/Bi pin. If a system reset

occur, the OC1A/B register is reset to “0”.

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Figure 12-5. Compare Match Output

PORTB0

OC1AU(*)

DDB0

PINB0

20 PB0/ OC1AU

PORTB2

WGM10

COM1A0

OCF1A

OCF1B

COM1A1

COM1B0

COM1B1

WGM11

WGM12

WGM13

OC1AV(*)

(*) OC1xi: TCCR1D register bit

DDB2

PINB2

Waveform

Generation

OCR1A

16-bit Register

OCR1B

16-bit Register

TCNT1

16-bit Counter

Waveform

Generation

18 PB2/ OC1AV

PORTB4

OC1AW(*)

DDB4

PINB4

14 PB4/ OC1AW

PORTB6

OC1AX(*)

DDB6

PINB6

12 PB6/ OC1AX

FOC1A

TOP

Count

Direction

Clear

BOTTOM

PORTB1

OC1BU(*)

DDB1

PINB1

19 PB1/ OC1BU

PORTB3

OC1BV(*)

DDB3

PINB3

17 PB3/ OC1BV

PORTB5

OC1BW(*)

DDB5

PINB5

13 PB5/ OC1BW

PORTB7

OC1BX(*)

DDB7

PINB7

11 PB7/ OC1BX

FOC1B

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Figure 12-6. Compare Match Output Logic

12.8.1 Compare Output Function

The general I/O port function is overridden by the output compare (OC1A/B) from the waveform generator if either of the

COM1A/B1:0 bits are set and if OCnxi respective bit is set in TCCR1D register. However, the OC1A/Bi pin direction (input or

output) is still controlled by the data direction register (DDR) for the port pin. The data direction register bit for the OC1A/Bi

pin (DDR_OC1A/Bi) must be set as output before the OC1A/B value is visible on the pin. The port override function is

generally independent of the waveform generation mode, but there are some exceptions. Refer to Table 12-1 on page 124,

Table 12-2 on page 124 and Table 12-3 on page 125 for details.

The design of the output compare pin logic allows initialization of the OC1A/B state before the output is enabled. Note that

some COM1A/B1:0 bit settings are reserved for certain modes of operation, see Section 12.11 “16-bit Timer/Counter

The COM1A/B1:0 bits have no effect on the input capture unit.

12.8.2 Compare Output Mode and Waveform Generation

The waveform generator uses the COM1A/B1:0 bits differently in normal, CTC, and PWM modes. For all modes, setting the

COM1A/B1:0 = 0 tells the waveform generator that no action on the OC1A/B register is to be performed on the next compare

match. For compare output actions in the non-PWM modes refer to Table 12-1 on page 124. For fast PWM mode refer to

Table 12-2 on page 124, and for phase correct and phase and frequency correct PWM refer to Table 12-3 on page 125.

A change of the COM1A/B1:0 bits state will have effect at the first compare match after the bits are written. For non-PWM

modes, the action can be forced to have immediate effect by using the FOC1A/B strobe bits.

12.9 Modes of Operation

The mode of operation, i.e., the behavior of the timer/counter and the output compare pins, is defined by the combination of

the waveform generation mode (WGM13:0) and compare output mode (COM1A/B1:0) bits. The compare output mode bits

do not affect the counting sequence, while the waveform generation mode bits do. The COM1A/B1:0 bits control whether the

PWM output generated should be inverted or not (inverted or non-inverted PWM). For non-PWM modes the COM1A/B1:0

bits control whether the output should be set, cleared or toggle at a compare match (see Section 12.8 “Compare Match

Output Unit” on page 113). The OCnxi bits over control the setting of the COM1A/B1:0 bits as shown in Figure 12-6 on page

115. For detailed timing information refer to Section 12.10 “Timer/Counter Timing Diagrams” on page 122.

DATA BUS

COMnx1

OCnxi

COMnx0

FOCnx

OCnx

Waveform

Generator

PORT

DDR

OCnxi

clkI/O

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12.9.1 Normal Mode

The simplest mode of operation is the normal mode (WGM13:0 = 0). In this mode the counting direction is always up

(incrementing), and no counter clear is performed. The counter simply overruns when it passes its maximum 16-bit value

(MAX = 0xFFFF) and then restarts from the BOTTOM (0x0000). In normal operation the timer/counter overflow flag (TOV1)

will be set in the same timer clock cycle as the TCNT1 becomes zero. The TOV1 flag in this case behaves like a 17th bit,

except that it is only set, not cleared. However, combined with the timer overflow interrupt that automatically clears the TOV1

flag, the timer resolution can be increased by software. There are no special cases to consider in the normal mode, a new

counter value can be written anytime.

The input capture unit is easy to use in normal mode. However, observe that the maximum interval between the external

events must not exceed the resolution of the counter. If the interval between events are too long, the timer overflow interrupt

or the prescaler must be used to extend the resolution for the capture unit.

The output compare units can be used to generate interrupts at some given time. Using the output compare to generate

waveforms in normal mode is not recommended, since this will occupy too much of the CPU time.

12.9.2 Clear Timer on Compare Match (CTC) Mode

In clear timer on compare or CTC mode (WGM13:0 = 4 or 12), the OCR1A or ICR1 register are used to manipulate the

counter resolution. In CTC mode the counter is cleared to zero when the counter value (TCNT1) matches either the OCR1A

(WGM13:0 = 4) or the ICR1 (WGM13:0 = 12). The OCR1A or ICR1 define the top value for the counter, hence also its

resolution. This mode allows greater control of the compare match output frequency. It also simplifies the operation of

counting external events.

The timing diagram for the CTC mode is shown in Figure 12-7. The counter value (TCNT1) increases until a compare match

occurs with either OCR1A or ICR1, and then counter (TCNT1) is cleared.

Figure 12-7. CTC Mode, Timing Diagram

An interrupt can be generated at each time the counter value reaches the TOP value by either using the OCF1A or ICF1 flag

according to the register used to define the TOP value. If the interrupt is enabled, the interrupt handler routine can be used

for updating the TOP value. However, changing the TOP to a value close to BOTTOM when the counter is running with none

or a low prescaler value must be done with care since the CTC mode does not have the double buffering feature. If the new

value written to OCR1A or ICR1 is lower than the current value of TCNT1, the counter will miss the compare match. The

counter will then have to count to its maximum value (0xFFFF) and wrap around starting at 0x0000 before the compare

match can occur. In many cases this feature is not desirable. An alternative will then be to use the fast PWM mode using

OCR1A for defining TOP (WGM13:0 = 15) since the OCR1A then will be double buffered.

For generating a waveform output in CTC mode, the OC1A output can be set to toggle its logical level on each compare

match by setting the compare output mode bits to toggle mode (COM1A1:0 = 1). The OC1A value will not be visible on the

port pin unless the data direction for the pin is set to output (DDR_OC1A = 1) and OC1Ai is set. The waveform generated will

have a maximum frequency of fOC1A = fclk_I/O/2 when OCR1A is set to zero (0x0000). The waveform frequency is defined by

the following equation:

TCNTn

(COMnA1:0 = 1)

OCnAi

(Toggle)

Period 3

OCnA Interrupt Flag Set

or ICFn Interrupt Flag Set

(Interrupt on TOP)

fOCnA

fclk_I/O

2N1OCRnA+

--------------------------------------------------

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The N variable represents the prescaler factor (1, 8, 64, 256, or 1024).

As for the normal mode of operation, the TOV1 flag is set in the same timer clock cycle that the counter counts from MAX to

0x0000.

12.9.3 Fast PWM Mode

The fast pulse width modulation or fast PWM mode (WGM13:0 = 5, 6, 7, 14, or 15) provides a high frequency PWM

waveform generation option. The fast PWM differs from the other PWM options by its single-slope operation. The counter

counts from BOTTOM to TOP then restarts from BOTTOM. In non-inverting compare output mode, the output compare

(OC1A/B) is set on the compare match between TCNT1 and OCR1A/B, and cleared at TOP. In inverting compare output

mode output is cleared on compare match and set at TOP. Due to the single-slope operation, the operating frequency of the

fast PWM mode can be twice as high as the phase correct and phase and frequency correct PWM modes that use dual-

slope operation. This high frequency makes the fast PWM mode well suited for power regulation, rectification, and DAC

applications. High frequency allows physically small sized external components (coils, capacitors), hence reduces total

system cost.

The PWM resolution for fast PWM can be fixed to 8-, 9-, or 10-bit, or defined by either ICR1 or OCR1A. The minimum

resolution allowed is 2-bit (ICR1 or OCR1A set to 0x0003), and the maximum resolution is 16-bit (ICR1 or OCR1A set to

MAX). The PWM resolution in bits can be calculated by using the following equation:

In fast PWM mode the counter is incremented until the counter value matches either one of the fixed values 0x00FF,

0x01FF, or 0x03FF (WGM13:0 = 5, 6, or 7), the value in ICR1 (WGM13:0 = 14), or the value in OCR1A (WGM13:0 = 15).

The counter is then cleared at the following timer clock cycle. The timing diagram for the fast PWM mode is shown in

Figure 12-8. The figure shows fast PWM mode when OCR1A or ICR1 is used to define TOP. The TCNT1 value is in the

timing diagram shown as a histogram for illustrating the single-slope operation. The diagram includes non-inverted and

inverted PWM outputs. The small horizontal line marks on the TCNT1 slopes represent compare matches between

OCR1A/B and TCNT1. The OC1A/B interrupt flag will be set when a compare match occurs.

Figure 12-8. Fast PWM Mode, Timing Diagram

The timer/counter overflow flag (TOV1) is set each time the counter reaches TOP. In addition the OC1A or ICF1 flag is set at

the same timer clock cycle as TOV1 is set when either OCR1A or ICR1 is used for defining the TOP value. If one of the

interrupts are enabled, the interrupt handler routine can be used for updating the TOP and compare values.

When changing the TOP value the program must ensure that the new TOP value is higher or equal to the value of all of the

compare registers. If the TOP value is lower than any of the compare registers, a compare match will never occur between

the TCNT1 and the OCR1A/B. Note that when using fixed TOP values the unused bits are masked to zero when any of the

OCR1A/B registers are written.

RFPWM TOP 1+log

2log

----------------------------------

12345

TCNTn

(COMnx1:0 = 2)

OCnxi

Period

OCRnx/ TOP Update and

TOVn Interrupt Flag Set and

OCnA Interrupt Flag Set

or ICFn Interrupt Flag Set

(Interrupt on TOP)

67 8

(COMnx1:0 = 3)

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The procedure for updating ICR1 differs from updating OCR1A when used for defining the TOP value. The ICR1 register is

not double buffered. This means that if ICR1 is changed to a low value when the counter is running with none or a low

prescaler value, there is a risk that the new ICR1 value written is lower than the current value of TCNT1. The result will then

be that the counter will miss the compare match at the TOP value. The counter will then have to count to the MAX value

(0xFFFF) and wrap around starting at 0x0000 before the compare match can occur. The OCR1A register however, is double

buffered. This feature allows the OCR1A I/O location to be written anytime. When the OCR1A I/O location is written the

value written will be put into the OCR1A buffer register. The OCR1A compare register will then be updated with the value in

the buffer register at the next timer clock cycle the TCNT1 matches TOP. The update is done at the same timer clock cycle

as the TCNT1 is cleared and the TOV1 flag is set.

Using the ICR1 register for defining TOP works well when using fixed TOP values. By using ICR1, the OCR1A register is

free to be used for generating a PWM output on OC1A. However, if the base PWM frequency is actively changed (by

changing the TOP value), using the OCR1A as TOP is clearly a better choice due to its double buffer feature.

In fast PWM mode, the compare units allow generation of PWM waveforms on the OC1A/B pins. Setting the COM1x1:0 bits

to two will produce a non-inverted PWM and an inverted PWM output can be generated by setting the COM1A/B1:0 to three

(see Table 12-2 on page 124). The actual OC1A/B value will only be visible on the port pin if the data direction for the port pin

is set as output (DDR_OC1A/B) and OC1A/Bi is set. The PWM waveform is generated by setting (or clearing) the OC1A/B

clock cycle the counter is cleared (changes from TOP to BOTTOM).

The PWM frequency for the output can be calculated by the following equation:

The N variable represents the prescaler divider (1, 8, 64, 256, or 1024).

The extreme values for the OCR1A/B register represents special cases when generating a PWM waveform output in the fast

PWM mode. If the OCR1A/B is set equal to BOTTOM (0x0000) the output will be a narrow spike for each TOP+1 timer clock

cycle. Setting the OCR1A/B equal to TOP will result in a constant high or low output (depending on the polarity of the output

set by the COM1A/B1:0 bits.)

A frequency (with 50% duty cycle) waveform output in fast PWM mode can be achieved by setting OC1A to toggle its logical

level on each compare match (COM1A1:0 = 1). The waveform generated will have a maximum frequency of fOC1A =

fclk_I/O/2 when OCR1A is set to zero (0x0000). This feature is similar to the OC1A toggle in CTC mode, except the double

buffer feature of the output compare unit is enabled in the fast PWM mode.

12.9.4 Phase Correct PWM Mode

The phase correct pulse width modulation or phase correct PWM mode (WGM13:0 = 1, 2, 3, 10, or 11) provides a high

resolution phase correct PWM waveform generation option. The phase correct PWM mode is, like the phase and frequency

correct PWM mode, based on a dual-slope operation. The counter counts repeatedly from BOTTOM (0x0000) to TOP and

then from TOP to BOTTOM. In non-inverting compare output mode, the output compare (OC1A/B) is cleared on the

compare match between TCNT1 and OCR1A/B while up counting, and set on the compare match while down counting. In

inverting output compare mode, the operation is inverted. The dual-slope operation has lower maximum operation frequency

than single slope operation. However, due to the symmetric feature of the dual-slope PWM modes, these modes are

preferred for motor control applications.

The PWM resolution for the phase correct PWM mode can be fixed to 8-, 9-, or 10-bit, or defined by either ICR1 or OCR1A.

The minimum resolution allowed is 2-bit (ICR1 or OCR1A set to 0x0003), and the maximum resolution is 16-bit (ICR1 or

OCR1A set to MAX). The PWM resolution in bits can be calculated by using the following equation:

fOCnxPWM

fclk_I/O

N1TOP+

----------------------------------

RPCPWM TOP 1+log

2log

----------------------------------

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In phase correct PWM mode the counter is incremented until the counter value matches either one of the fixed values

0x00FF, 0x01FF, or 0x03FF (WGM13:0 = 1, 2, or 3), the value in ICR1 (WGM13:0 = 10), or the value in OCR1A

(WGM13:0 = 11). The counter has then reached the TOP and changes the count direction. The TCNT1 value will be equal to

TOP for one timer clock cycle. The timing diagram for the phase correct PWM mode is shown on Figure 12-9. The figure

shows phase correct PWM mode when OCR1A or ICR1 is used to define TOP. The TCNT1 value is in the timing diagram

shown as a histogram for illustrating the dual-slope operation. The diagram includes non-inverted and inverted PWM

outputs. The small horizontal line marks on the TCNT1 slopes represent compare matches between OCR1A/B and TCNT1.

The OC1A/B interrupt flag will be set when a compare match occurs.

Figure 12-9. Phase Correct PWM Mode, Timing Diagram

The timer/counter overflow flag (TOV1) is set each time the counter reaches BOTTOM. When either OCR1A or ICR1 is used

for defining the TOP value, the OC1A or ICF1 flag is set accordingly at the same timer clock cycle as the OCR1A/B registers

are updated with the double buffer value (at TOP). The interrupt flags can be used to generate an interrupt each time the

counter reaches the TOP or BOTTOM value.

When changing the TOP value the program must ensure that the new TOP value is higher or equal to the value of all of the

compare registers. If the TOP value is lower than any of the compare registers, a compare match will never occur between

the TCNT1 and the OCR1A/B. Note that when using fixed TOP values, the unused bits are masked to zero when any of the

OCR1A/B registers are written. As the third period shown in Figure 12-9 illustrates, changing the TOP actively while the

timer/counter is running in the phase correct mode can result in an unsymmetrical output. The reason for this can be found in

the time of update of the OCR1A/B register. Since the OCR1A/B update occurs at TOP, the PWM period starts and ends at

TOP. This implies that the length of the falling slope is determined by the previous TOP value, while the length of the rising

slope is determined by the new TOP value. When these two values differ the two slopes of the period will differ in length. The

difference in length gives the unsymmetrical result on the output.

It is recommended to use the phase and frequency correct mode instead of the phase correct mode when changing the TOP

value while the timer/counter is running. When using a static TOP value there are practically no differences between the two

modes of operation.

1234

TCNTn

(COMnx1:0 = 2)

(COMnx1:0 = 3)

OCnxi

Period

TOVn Interrupt Flag Set

(Interrupt on Bottom)

OCRnx/ TOP Update and

OCnA Interrupt Flag Set

or ICFn Interrupt Flag Set

(Interrupt on TOP)

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In phase correct PWM mode, the compare units allow generation of PWM waveforms on the OC1A/B pins. Setting the

COM1A/B1:0 bits to two will produce a non-inverted PWM and an inverted PWM output can be generated by setting the

COM1A/B1:0 to three (See Table on page 125). The actual OC1A/B value will only be visible on the port pin if the data

direction for the port pin is set as output (DDR_OC1A/B) and OC1A/Bi is set. The PWM waveform is generated by setting (or

clearing) the OC1A/B register at the compare match between OCR1A/B and TCNT1 when the counter increments, and

clearing (or setting) the OC1A/B Register at compare match between OCR1A/B and TCNT1 when the counter decrements.

The PWM frequency for the output when using phase correct PWM can be calculated by the following equation:

The N variable represents the prescaler divider (1, 8, 64, 256, or 1024).

The extreme values for the OCR1A/B register represent special cases when generating a PWM waveform output in the

phase correct PWM mode. If the OCR1A/B is set equal to BOTTOM the output will be continuously low and if set equal to

TOP the output will be continuously high for non-inverted PWM mode. For inverted PWM the output will have the opposite

logic values.

12.9.5 Phase and Frequency Correct PWM Mode

The phase and frequency correct pulse width modulation, or phase and frequency correct PWM mode (WGM13:0 = 8 or 9)

provides a high resolution phase and frequency correct PWM waveform generation option. The phase and frequency correct

PWM mode is, like the phase correct PWM mode, based on a dual-slope operation. The counter counts repeatedly from

BOTTOM (0x0000) to TOP and then from TOP to BOTTOM. In non-inverting compare output mode, the output compare

(OC1A/B) is cleared on the compare match between TCNT1 and OCR1A/B while up counting, and set on the compare

match while down counting. In inverting compare output mode, the operation is inverted. The dual-slope operation gives a

lower maximum operation frequency compared to the single-slope operation. However, due to the symmetric feature of the

dual-slope PWM modes, these modes are preferred for motor control applications.

The main difference between the phase correct, and the phase and frequency correct PWM mode is the time the OCR1A/B

The PWM resolution for the phase and frequency correct PWM mode can be defined by either ICR1 or OCR1A. The

minimum resolution allowed is 2-bit (ICR1 or OCR1A set to 0x0003), and the maximum resolution is 16-bit (ICR1 or OCR1A

set to MAX). The PWM resolution in bits can be calculated using the following equation

In phase and frequency correct PWM mode the counter is incremented until the counter value matches either the value in

ICR1 (WGM13:0 = 8), or the value in OCR1A (WGM13:0 = 9). The counter has then reached the TOP and changes the

count direction. The TCNT1 value will be equal to TOP for one timer clock cycle. The timing diagram for the phase correct

and frequency correct PWM mode is shown on Figure 12-10 on page 121. The figure shows phase and frequency correct

PWM mode when OCR1A or ICR1 is used to define TOP. The TCNT1 value is in the timing diagram shown as a histogram

for illustrating the dual-slope operation. The diagram includes non-inverted and inverted PWM outputs. The small horizontal

line marks on the TCNT1 slopes represent compare matches between OCR1A/B and TCNT1. The OC1A/B interrupt flag will

be set when a compare match occurs.

fOCnxPCPWM

fclk_I/O

2NTOP

----------------------------

RPFCPWM TOP 1+log

2log

----------------------------------

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Figure 12-10.Phase and Frequency Correct PWM Mode, Timing Diagram

The timer/counter overflow flag (TOV1) is set at the same timer clock cycle as the OCR1A/B registers are updated with the

double buffer value (at BOTTOM). When either OCR1A or ICR1 is used for defining the TOP value, the OC1A or ICF1 flag

set when TCNT1 has reached TOP. The interrupt flags can then be used to generate an interrupt each time the counter

reaches the TOP or BOTTOM value.

When changing the TOP value the program must ensure that the new TOP value is higher or equal to the value of all of the

compare registers. If the TOP value is lower than any of the compare registers, a compare match will never occur between

the TCNT1 and the OCR1A/B.

As Figure 12-10 shows the output generated is, in contrast to the phase correct mode, symmetrical in all periods. Since the

OCR1A/B registers are updated at BOTTOM, the length of the rising and the falling slopes will always be equal. This gives

symmetrical output pulses and is therefore frequency correct.

Using the ICR1 register for defining TOP works well when using fixed TOP values. By using ICR1, the OCR1A register is

free to be used for generating a PWM output on OC1A. However, if the base PWM frequency is actively changed by

changing the TOP value, using the OCR1A as TOP is clearly a better choice due to its double buffer feature.

In phase and frequency correct PWM mode, the compare units allow generation of PWM waveforms on the OC1A/B pins.

Setting the COM1A/B1:0 bits to two will produce a non-inverted PWM and an inverted PWM output can be generated by

setting the COM1A/B1:0 to three (See Table on page 125). The actual OC1A/B value will only be visible on the port pin if the

data direction for the port pin is set as output (DDR_OC1A/B) and OC1A/Bi is set. The PWM waveform is generated by

setting (or clearing) the OC1A/B register at the compare match between OCR1A/B and TCNT1 when the counter

increments, and clearing (or setting) the OC1A/B register at compare match between OCR1A/B and TCNT1 when the

counter decrements. The PWM frequency for the output when using phase and frequency correct PWM can be calculated by

the following equation:

The N variable represents the prescaler divider (1, 8, 64, 256, or 1024).

The extreme values for the OCR1A/B register represents special cases when generating a PWM waveform output in the

phase correct PWM mode. If the OCR1A/B is set equal to BOTTOM the output will be continuously low and if set equal to

TOP the output will be set to high for non-inverted PWM mode. For inverted PWM the output will have the opposite logic

values.

1234

TCNTn

(COMnx1:0 = 2)

(COMnx1:0 = 3)

OCnxi

Period

OCnA Interrupt Flag Set

or ICFn Interrupt Flag Set

(Interrupt on TOP)

OCRnx/ TOP Update and

TOVn Interrupt Flag Set

(Interrupt on Bottom)

fOCnxPFCPWM

fclk_I/O

2NTOP

----------------------------

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12.10 Timer/Counter Timing Diagrams

The timer/counter is a synchronous design and the timer clock (clkT1) is therefore shown as a clock enable signal in the

following figures. The figures include information on when interrupt flags are set, and when the OCR1A/B register is updated

with the OCR1A/B buffer value (only for modes utilizing double buffering). Figure 12-11 shows a timing diagram for the

setting of OCF1A/B.

Figure 12-11.Timer/Counter Timing Diagram, Setting of OCF1A/B, no Prescaling

Figure 12-12 shows the same timing data, but with the prescaler enabled.

Figure 12-12.Timer/Counter Timing Diagram, Setting of OCF1A/B, with Prescaler (fclk_I/O/8)

OCRnx - 1

clkI/O

(clkI/O/8)

TCNTn

OCRnx

OCFnx

clkTn

OCRnx OCRnx + 1

OCRnx Value

OCRnx + 2

OCRnx - 1

clkI/O

(clkI/O/8)

TCNTn

OCRnx

OCFnx

clkTn

OCRnx OCRnx + 1

OCRnx Value

OCRnx + 2

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Figure 12-13 shows the count sequence close to TOP in various modes. When using phase and frequency correct PWM

mode the OCR1A/B Register is updated at BOTTOM. The timing diagrams will be the same, but TOP should be replaced by

BOTTOM, TOP-1 by BOTTOM+1 and so on. The same renaming applies for modes that set the TOV1 flag at BOTTOM.

Figure 12-13.Timer/Counter Timing Diagram, no Prescaling

Figure 12-14 shows the same timing data, but with the prescaler enabled.

Figure 12-14.Timer/Counter Timing Diagram, with Prescaler (fclk_I/O/8)

TOP - 1

clkI/O

(clkI/O/1)

TCNTn

(CTC and FPWM)

OCRnx

(Update at TOP)

TCNTn

(PC and PFC PWM)

TOVn (FPWM)

and ICFn

(if used as TOP)

clkTn

TOP

Old OCRnx Value New OCRnx Value

BOTTOM BOTTOM + 1

TOP - 1 TOP TOP -1 TOP -2

TOP - 1 TOP BOTTOM BOTTOM + 1

TOP - 1 TOP TOP - 1 TOP - 2

clkI/O

(clkI/O/8)

TCNTn

(CTC and FPWM)

OCRnx

(Update at TOP)

TCNTn

(PC and PFC PWM)

TOVn (FPWM)

and ICFn

(if used as TOP)

clkTn

Old OCRnx Value New OCRnx Value

Nme: 1. A special case occurs when OCR1A/OCR1 B equals TOP and COM1A1/COM1 B1 is set. In Ihis case the com- AtmeL

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12.11 16-bit Timer/Counter Register Description

12.11.1 Timer/Counter1 Control Register A – TCCR1A

• Bit 7:6 – COM1A1:0: Compare Output Mode for Channel A

• Bit 5:4 – COM1B1:0: Compare Output Mode for Channel B

The COM1A1:0 and COM1B1:0 control the output compare pins (OC1Ai and OC1Bi respectively) behavior. If one or both of

the COM1A1:0 bits are written to one, the OC1Ai output overrides the normal port functionality of the I/O pin it is connected

to. If one or both of the COM1B1:0 bit are written to one, the OC1Bi output overrides the normal port functionality of the I/O

pin it is connected to. However, note that the data direction register (DDR) bit and OC1xi bit (TCCR1D) corresponding to the

OC1Ai or OC1Bi pin must be set in order to enable the output driver.

When the OC1Ai or OC1Bi is connected to the pin, the function of the COM1A/B1:0 bits is dependent of the WGM13:0 bits

setting. Table 12-1 shows the COM1A/B1:0 bit functionality when the WGM13:0 bits are set to a Normal or a CTC mode

(non-PWM).

Table 12-2 shows the COM1A/B1:0 bit functionality when the WGM13:0 bits are set to the fast PWM mode.

Bit 76543210

COM1A1 COM1A0 COM1B1 COM1B0 – – WGM11 WGM10 TCCR1A

Read/Write R/W R/W R/W R/W R R R/W R/W

Initial Value 0 0 0 0 0 0 0 0

Table 12-1. Compare Output Mode, non-PWM

OC1Ai

OC1Bi

COM1A1

COM1B1

COM1A0

COM1B0 Description

0 x x Normal port operation, OC1A/OC1B disconnected.

0 0

0 1 Toggle OC1A/OC1B on compare match.

1 0 Clear OC1A/OC1B on compare match (set output to low level).

1 1 Set OC1A/OC1B on compare match (set output to high level).

Table 12-2. Compare Output Mode, Fast PWM (1)

OC1Ai

OC1Bi

COM1A1

COM1B1

COM1A0

COM1B0 Description

0 x x Normal port operation, OC1A/OC1B disconnected.

1 0 0

1 0 1 WGM13=0: Normal port operation, OC1A/OC1B disconnected.

WGM13=1: Toggle OC1A on compare match, OC1B reserved.

1 1 0 Clear OC1A/OC1B on compare match

Set OC1A/OC1B at TOP

1 1 1 Set OC1A/OC1B on compare match

Clear OC1A/OC1B at TOP

Note: 1. A special case occurs when OCR1A/OCR1B equals TOP and COM1A1/COM1B1 is set. In this case the com-

pare match is ignored, but the set or clear is done at TOP. See Section 12.9.3 “Fast PWM Mode” on page 117

for more details.

Note: 1. A special case occurs wnen OC1A/OC1B equals TOP and COM1A1/COM1B1 is set. See Section 12.9.4 Notes: 1. The CTC1 and PWM11:0 bit definition names are obsolete. Use tne WGM12:0 deﬁnitions. However. the functionality AtmeL

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Table 12-3 shows the COM1A/B1:0 bit functionality when the WGM13:0 bits are set to the phase correct or the phase and

frequency correct, PWM mode.

• Bit 3:2 – Reserved Bits

These bits are reserved for future use.

• Bit 1:0 – WGM11:0: Waveform Generation Mode

Combined with the WGM13:2 bits found in the TCCR1B register, these bits control the counting sequence of the counter, the

source for maximum (TOP) counter value, and what type of waveform generation to be used, see Table 12-4. Modes of

operation supported by the timer/counter unit are: normal mode (counter), Clear timer on compare match (CTC) mode, and

three types of pulse width modulation (PWM) modes (see Section 12.9 “Modes of Operation” on page 115).

Table 12-3. Compare Output Mode, Phase Correct and Phase and Frequency Correct PWM(1)

OC1Ai

OC1Bi

COM1A1

COM1B1

COM1A0

COM1B0 Description

0 x x Normal port operation, OC1A/OC1B disconnected.

1 0 0

1 0 1 WGM13=0: Normal port operation, OC1A/OC1B disconnected.

WGM13=1: Toggle OC1A on compare match, OC1B reserved.

1 1 0 Clear OC1A/OC1B on compare match when up-counting.

Set OC1A/OC1B on compare match when downcounting.

1 1 1 Set OC1A/OC1B on compare match when up-counting.

Clear OC1A/OC1B on compare match when downcounting.

Note: 1. A special case occurs when OC1A/OC1B equals TOP and COM1A1/COM1B1 is set. See Section 12.9.4

“Phase Correct PWM Mode” on page 118 for more details.

Table 12-4. Waveform Generation Mode Bit Description (1)

Mode WGM13

WGM12

(CTC1)

WGM11

(PWM11)

WGM10

(PWM10)

Timer/Counter

Mode of Operation TOP

Update of

OCR1A/B at

TOV1 Flag

Set on

0 0 0 0 0 Normal 0xFFFF Immediate MAX

1 0 0 0 1 PWM, phase correct, 8-bit 0x00FF TOP BOTTOM

2 0 0 1 0 PWM, phase correct, 9-bit 0x01FF TOP BOTTOM

3 0 0 1 1 PWM, phase correct, 10-bit 0x03FF TOP BOTTOM

4 0 1 0 0 CTC OCR1A Immediate MAX

5 0 1 0 1 Fast PWM, 8-bit 0x00FF TOP TOP

6 0 1 1 0 Fast PWM, 9-bit 0x01FF TOP TOP

7 0 1 1 1 Fast PWM, 10-bit 0x03FF TOP TOP

8 1 0 0 0 PWM, phase and frequency

correct ICR1 BOTTOM BOTTOM

9 1 0 0 1 PWM, phase and frequency

correct OCR1A BOTTOM BOTTOM

10 1 0 1 0 PWM, phase correct ICR1 TOP BOTTOM

11 1 0 1 1 PWM, phase correct OCR1A TOP BOTTOM

12 1 1 0 0 CTC ICR1 Immediate MAX

13 1 1 0 1 (Reserved) – – –

14 1 1 1 0 Fast PWM ICR1 TOP TOP

15 1 1 1 1 Fast PWM OCR1A TOP TOP

Notes: 1. The CTC1 and PWM11:0 bit definition names are obsolete. Use the WGM12:0 definitions. However, the functionality

and location of these bits are compatible with previous versions of the timer.

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12.11.2 Timer/Counter1 Control Register B – TCCR1B

• Bit 7 – ICNC1: Input Capture Noise Canceler

Setting this bit (to one) activates the input capture noise canceler. When the noise canceler is activated, the input from the

input capture pin (ICP1) is filtered. The filter function requires four successive equal valued samples of the ICP1 pin for

changing its output. The input capture is therefore delayed by four oscillator cycles when the noise canceler is enabled.

• Bit 6 – ICES1: Input Capture Edge Select

This bit selects which edge on the input capture pin (ICP1) that is used to trigger a capture event. When the ICES1 bit is

written to zero, a falling (negative) edge is used as trigger, and when the ICES1 bit is written to one, a rising (positive) edge

will trigger the capture.

When a capture is triggered according to the ICES1 setting, the counter value is copied into the input capture register

(ICR1). The event will also set the input capture flag (ICF1), and this can be used to cause an Input capture interrupt, if this

interrupt is enabled.

When the ICR1 is used as TOP value (see description of the WGM13:0 bits located in the TCCR1A and the TCCR1B

• Bit 5 – Reserved Bit

This bit is reserved for future use. For ensuring compatibility with future devices, this bit must be written to zero when

TCCR1B is written.

• Bit 4:3 – WGM13:2: Waveform Generation Mode

See TCCR1A register description.

• Bit 2:0 – CS12:0: Clock Select

The three Clock Select bits select the clock source to be used by the Timer/Counter, see Figure 12-11 on page 122 and

Figure 12-12 on page 122.

If external pin modes are used for the timer/counter1, transitions on the T1 pin will clock the counter even if the pin is

configured as an output. This feature allows software control of the counting.

Bit 76543210

ICNC1 ICES1 – WGM13 WGM12 CS12 CS11 CS10 TCCR1B

Read/Write R/W R/W R R/W R/W R/W R/W R/W

Initial Value 0 0 0 0 0 0 0 0

Table 12-5. Clock Select Bit Description

CS12 CS11 CS10 Description

000No clock source (timer/counter stopped).

001clkI/O/1 (no prescaling)

010clkI/O/8 (from prescaler)

011clkI/O/64 (from prescaler)

100clkI/O/256 (from prescaler)

101clkI/O/1024 (from prescaler)

110External clock source on T1 pin. Clock on falling edge.

111External clock source on T1 pin. Clock on rising edge.

AtmeL T—CNT1l15:B] _R/w Fuw RIW RNV 'le Fuw Fuw RNV

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12.11.3 Timer/Counter1 Control Register C – TCCR1C

• Bit 7 – FOC1A: Force Output Compare for Channel A

• Bit 6 – FOC1B: Force Output Compare for Channel B

The FOC1A/FOC1B bits are only active when the WGM13:0 bits specifies a non-PWM mode. However, for ensuring

compatibility with future devices, these bits must be set to zero when TCCR1A is written when operating in a PWM mode.

When writing a logical one to the FOC1A/FOC1B bit, an immediate compare match is forced on the waveform generation

unit. The OC1nx output is changed according to its COM1A/B1:0 and OC1nx bits setting. Note that the FOC1A/FOC1B bits

are implemented as strobes. Therefore it is the value present in the COM1A/B1:0 bits that determine the effect of the forced

compare.

A FOC1A/FOC1B strobe will not generate any interrupt nor will it clear the timer in clear timer on compare match (CTC)

mode using OCR1A as TOP.

The FOC1A/FOC1B bits are always read as zero.

12.11.4 Timer/Counter1 Control Register D – TCCR1D

• Bit 7:4 – OC1Bi: Output Compare Pin Enable for Channel B

The OC1Bi bits enable the output compare pins of channel B as shown in Figure 12-6 on page 115.

• Bit 3:0 – OC1Ai: Output Compare Pin Enable for Channel A

The OC1Ai bits enable the output compare pins of channel A as shown in Figure 12-6 on page 115.

12.11.5 Timer/Counter1 – TCNT1H and TCNT1L

The two timer/counter I/O locations (TCNT1H and TCNT1L, combined TCNT1) give direct access, both for read and for write

operations, to the timer/counter unit 16-bit counter. To ensure that both the high and low bytes are read and written

simultaneously when the CPU accesses these registers, the access is performed using an 8-bit temporary high byte register

(TEMP). This temporary register is shared by all the other 16-bit registers, see Section 12.3 “Accessing 16-bit Registers” on

page 105.

Modifying the counter (TCNT1) while the counter is running introduces a risk of missing a compare match between TCNT1

and one of the OCR1A/B registers.

Writing to the TCNT1 register blocks (removes) the compare match on the following timer clock for all compare units.

Bit 76543210

FOC1A FOC1B – – – – – – TCCR1C

Read/Write R/W R/W R/W R R R R R

Initial Value 0 0 0 0 0 0 0 0

Bit 76543210

OC1BX OC1BW OC1BV OC1BU OC1AX OC1AW OC1AV OC1AU TCCR1D

Read/Write R/W R/W R/W R/W R/W R/W R/W R/W

Initial Value 0 0 0 0 0 0 0 0

Bit 76543210

TCNT1[15:8] TCNT1H

TCNT1[7:0] TCNT1L

Read/Write R/W R/W R/W R/W R/W R/W R/W R/W

Initial Value00000000

OCR1A[15:3] RM RM RM RM] RM] RM] RM] R/W OCR1E[15:3] RM RM RM RM] RM] RM] RM RM ICR1[15:8] R/W R/W RM RM] RM] RM] RM RM AtmeL

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12.11.6 Output Compare Register A – OCR1AH and OCR1AL

12.11.7 Output Compare Register B – OCR1BH and OCR1BL

The output compare registers contain a 16-bit value that is continuously compared with the counter value (TCNT1). A match

can be used to generate an output compare interrupt, or to generate a waveform output on the OC1A/B pin.

The output compare registers are 16-bit in size. To ensure that both the high and low bytes are written simultaneously when

the CPU writes to these registers, the access is performed using an 8-bit temporary high byte register (TEMP). This

temporary register is shared by all the other 16-bit registers, see Section 12.3 “Accessing 16-bit Registers” on page 105.

12.11.8 Input Capture Register – ICR1H and ICR1L

The input capture is updated with the counter (TCNT1) value each time an event occurs on the ICP1 pin (or optionally on the

analog comparator output for timer/counter1). The input capture can be used for defining the counter TOP value.

The input capture register is 16-bit in size. To ensure that both the high and low bytes are read simultaneously when the

CPU accesses these registers, the access is performed using an 8-bit temporary high byte register (TEMP). This temporary

12.11.9 Timer/Counter1 Interrupt Mask Register – TIMSK1

• Bit 7..6 – Reserved Bits

These bits are reserved for future use.

• Bit 5 – ICIE1: Input Capture Interrupt Enable

When this bit is written to one, and the I-flag in the status register is set (interrupts globally enabled), the timer/counter1 input

capture interrupt is enabled. The corresponding interrupt vector (see Section 7.1 “Interrupt Vectors in ATtiny87/167” on page

57) is executed when the ICF1 flag, located in TIFR1, is set.

• Bit 4..3 – Reserved Bits

These bits are reserved for future use.

Bit 76543210

OCR1A[15:8] OCR1AH

OCR1A[7:0] OCR1AL

Read/Write R/W R/W R/W R/W R/W R/W R/W R/W

Initial Value00000000

Bit 76543210

OCR1B[15:8] OCR1BH

OCR1B[7:0] OCR1BL

Read/Write R/W R/W R/W R/W R/W R/W R/W R/W

Initial Value00000000

Bit 76543210

ICR1[15:8] ICR1H

ICR1[7:0] ICR1L

Read/Write R/W R/W R/W R/W R/W R/W R/W R/W

Initial Value00000000

Bit 76543210

– – ICIE1 – – OCIE1B OCIE1A TOIE1 TIMSK1

Read/Write R R R/W R R R/W R/W R/W

Initial Value00000000

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• Bit 2 – OCIE1B: Output Compare B Match Interrupt Enable

When this bit is written to one, and the I-flag in the status register is set (interrupts globally enabled), the timer/counter1

output compare B match interrupt is enabled. The corresponding interrupt vector (see Section 7.1 “Interrupt Vectors in

ATtiny87/167” on page 57) is executed when the OCF1B flag, located in TIFR1, is set.

• Bit 1 – OCIE1A: Output Compare A Match Interrupt Enable

When this bit is written to one, and the I-flag in the status register is set (interrupts globally enabled), the timer/counter1

output compare A match interrupt is enabled. The corresponding interrupt vector (see Section 7.1 “Interrupt Vectors in

ATtiny87/167” on page 57) is executed when the OCF1A flag, located in TIFR1, is set.

• Bit 0 – TOIE1: Timer/Counter Overflow Interrupt Enable

When this bit is written to one, and the I-flag in the status register is set (interrupts globally enabled), the timer/counter1

overflow interrupt is enabled. The corresponding interrupt vector (see Section 7.1 “Interrupt Vectors in ATtiny87/167” on

page 57) is executed when the TOV1 flag, located in TIFR1, is set.

12.11.10 Timer/Counter1 Interrupt Flag Register – TIFR1

• Bit 7..6 – Reserved Bits

These bits are reserved for future use.

• Bit 5 – ICF1: Input Capture Flag

This flag is set when a capture event occurs on the ICP1 pin. When the input capture register (ICR1) is set by the WGM13:0

to be used as the TOP value, the ICF1 flag is set when the counter reaches the TOP value.

ICF1 is automatically cleared when the input capture interrupt vector is executed. Alternatively, ICF1 can be cleared by

writing a logic one to its bit location.

• Bit 4..3 – Reserved Bits

These bits are reserved for future use.

• Bit 2 – OCF1B: Output Compare B Match Flag

This flag is set in the timer clock cycle after the counter (TCNT1) value matches the output compare register B (OCR1B).

Note that a forced output compare (FOC1B) strobe will not set the OCF1B flag.

OCF1B is automatically cleared when the output compare match B interrupt vector is executed. Alternatively, OCF1B can be

cleared by writing a logic one to its bit location.

• Bit 1 – OCF1A: Output Compare A Match Flag

This flag is set in the timer clock cycle after the counter (TCNT1) value matches the output compare register A (OCR1A).

Note that a forced output compare (FOC1A) strobe will not set the OCF1A flag.

OCF1A is automatically cleared when the output compare match A interrupt vector is executed. Alternatively, OCF1A can be

cleared by writing a logic one to its bit location.

• Bit 0 – TOV1: Timer/Counter Overflow Flag

The setting of this flag is dependent of the WGM13:0 bits setting. In normal and CTC modes, the TOV1 flag is set when the

timer overflows. Refer to Table 12-4 on page 125 for the TOV1 flag behavior when using another WGM13:0 bit setting.

TOV1 is automatically cleared when the timer/counter1 overflow interrupt vector is executed. Alternatively, TOV1 can be

cleared by writing a logic one to its bit location.

Bit 76543210

––ICF1––OCF1BOCF1ATOV1TIFR1

Read/Write R R R/W R R R/W R/W R/W

Initial Value00000000

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13. SPI - Serial Peripheral Interface

The serial peripheral interface (SPI) allows high-speed synchronous data transfer between the Atmel® ATtiny87/167 and

peripheral devices or between several AVR® devices. The Atmel ATtiny87/167 SPI includes the following features:

13.1 Features

●Full-duplex, three-wire synchronous data transfer

●Master or slave operation

●LSB first or MSB first data transfer

●Seven programmable bit rates

●End of transmission interrupt flag

●Write collision flag protection

●Wake-up from idle mode

●Double speed (CK/2) master SPI mode

Figure 13-1. SPI Block Diagram(1)

Note: 1. Refer to Figure 1.6 on page 6, and Table 9-3 on page 73 for SPI pin placement.

The interconnection between master and slave CPUs with SPI is shown in Figure 13-2 on page 131. The system consists of

two shift registers, and a master clock generator. The SPI master initiates the communication cycle when pulling low the

slave select SS pin of the desired slave. Master and slave prepare the data to be sent in their respective shift registers, and

the master generates the required clock pulses on the SCK line to interchange data. Data is always shifted from master to

slave on the master Out – slave in, MOSI, line, and from slave to master on the master in – slave out, MISO, line. After each

data packet, the master will synchronize the slave by pulling high the slave select, SS, line.

8-Bit Shift Register

Read Data Buffer

SPI Control RegisterSPI Status Register

MSTR

SPI Clock (Master)

SPE

SPI Control

SPI Interrupt

Request

Select Clock

Logic

MISO

Clock

MSB LSB

SPIE

SPE

WCOL

SPIF

SPI2X

SPR1

MSTR

SPE

DORD

SPR0

DORD

MSTR

CPOL

CPHA

SPR1

SPR0

MOSI

SCK

Divider

/2/4/8/16/32/64/128

clkI/O

Internal

Data Bus

Control

Logic

Note: 1. See Section 9.3.4 “Alternate Functions of Port B" on page 8 for a detailed description of how to deﬁne the AtmeL

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When configured as a master, the SPI interface has no automatic control of the SS line. This must be handled by user

software before communication can start. When this is done, writing a byte to the SPI data register starts the SPI clock

generator, and the hardware shifts the eight bits into the slave. After shifting one byte, the SPI clock generator stops, setting

the end of transmission flag (SPIF). If the SPI interrupt enable bit (SPIE) in the SPCR register is set, an interrupt is

requested. The master may continue to shift the next byte by writing it into SPDR, or signal the end of packet by pulling high

the slave select, SS line. The last incoming byte will be kept in the buffer register for later use.

When configured as a slave, the SPI interface will remain sleeping with MISO tri-stated as long as the SS pin is driven high.

In this state, software may update the contents of the SPI data register, SPDR, but the data will not be shifted out by

incoming clock pulses on the SCK pin until the SS pin is driven low. As one byte has been completely shifted, the end of

transmission flag, SPIF is set. If the SPI interrupt enable bit, SPIE, in the SPCR register is set, an interrupt is requested. The

slave may continue to place new data to be sent into SPDR before reading the incoming data. The last incoming byte will be

kept in the buffer register for later use.

Figure 13-2. SPI Master-slave Interconnection

The system is single buffered in the transmit direction and double buffered in the receive direction. This means that bytes to

be transmitted cannot be written to the SPI data register before the entire shift cycle is completed. When receiving data,

however, a received character must be read from the SPI data register before the next character has been completely

shifted in. Otherwise, the first byte is lost.

In SPI slave mode, the control logic will sample the incoming signal of the SCK pin. To ensure correct sampling of the clock

signal, the frequency of the SPI clock should never exceed fclkio/4.

When the SPI is enabled, the data direction of the MOSI, MISO, SCK, and SS pins is overridden according to Table 13-1. For

more details on automatic port overrides, refer to Section 9.3 “Alternate Port Functions” on page 70.

Table 13-1. SPI Pin Overrides(1)

Pin Direction, Master SPI Direction, Slave SPI

MOSI User defined Input

MISO Input User defined

SCK User defined Input

SS User defined Input

Note: 1. See Section 9.3.4 “Alternate Functions of Port B” on page 78 for a detailed description of how to define the

direction of the user defined SPI pins.

LSBSLAVEMSB

8 Bit Shift Register

LSB

Shift

Enable

MASTERMSB

SCK

MOSIMOSI

MISOMISO

8 Bit Shift Register

SPI

Clock Generator

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The following code examples show how to initialize the SPI as a master and how to perform a simple transmission.

DDR_SPI in the examples must be replaced by the actual data direction register controlling the SPI pins. DD_MOSI,

DD_MISO and DD_SCK must be replaced by the actual data direction bits for these pins. E.g. if MOSI is placed on pin PB2,

replace DD_MOSI with DDB2 and DDR_SPI with DDRB.

Note: 1. The example code assumes that the part specific header file is included.

Assembly Code Example(1)

SPI_MasterInit:

; Set MOSI and SCK output, all others input

ldi r17,(1<<DD_MOSI)|(1<<DD_SCK)

out DDR_SPI,r17

; Enable SPI, Master, set clock rate fck/16

ldi r17,(1<<SPE)|(1<<MSTR)|(1<<SPR0)

out SPCR,r17

ret

SPI_MasterTransmit:

; Start transmission of data (r16)

out SPDR,r16

Wait_Transmit:

; Wait for transmission complete

in r17,SPSR

sbrs r17,SPIF

rjmp Wait_Transmit

ret

C Code Example(1)

void SPI_MasterInit(void)

{

/* Set MOSI and SCK output, all others input */

DDR_SPI = (1<<DD_MOSI)|(1<<DD_SCK);

/* Enable SPI, Master, set clock rate fck/16 */

SPCR = (1<<SPE)|(1<<MSTR)|(1<<SPR0);

}

void SPI_MasterTransmit(char cData)

{

/* Start transmission */

SPDR = cData;

/* Wait for transmission complete */

while(!(SPSR & (1<<SPIF)));

}

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The following code examples show how to initialize the SPI as a slave and how to perform a simple reception.

Note: 1. The example code assumes that the part specific header file is included.

Assembly Code Example(1)

SPI_SlaveInit:

; Set MISO output, all others input

ldi r17,(1<<DD_MISO)

out DDR_SPI,r17

; Enable SPI

ldi r17,(1<<SPE)

out SPCR,r17

ret

SPI_SlaveReceive:

; Wait for reception complete

sbis SPSR,SPIF

rjmp SPI_SlaveReceive

; Read received data and return

in r16,SPDR

ret

C Code Example(1)

void SPI_SlaveInit(void)

{

/* Set MISO output, all others input */

DDR_SPI = (1<<DD_MISO);

/* Enable SPI */

SPCR = (1<<SPE);

}

char SPI_SlaveReceive(void)

{

/* Wait for reception complete */

while(!(SPSR & (1<<SPIF)));

/* Return data register */

return SPDR;

}

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13.2 SS Pin Functionality

13.2.1 Slave Mode

When the SPI is configured as a slave, the slave select (SS) pin is always input. When SS is held low, the SPI is activated,

and MISO becomes an output if configured so by the user. All other pins are inputs. When SS is driven high, all pins are

inputs, and the SPI is passive, which means that it will not receive incoming data. Note that the SPI logic will be reset once

the SS pin is driven high.

The SS pin is useful for packet/byte synchronization to keep the slave bit counter synchronous with the master clock

generator. When the SS pin is driven high, the SPI slave will immediately reset the send and receive logic, and drop any

partially received data in the shift register.

13.2.2 Master Mode

When the SPI is configured as a master (MSTR in SPCR is set), the user can determine the direction of the SS pin.

If SS is configured as an output, the pin is a general output pin which does not affect the SPI system. Typically, the pin will be

driving the SS pin of the SPI slave.

If SS is configured as an input, it must be held high to ensure master SPI operation. If the SS pin is driven low by peripheral

circuitry when the SPI is configured as a master with the SS pin defined as an input, the SPI system interprets this as

another master selecting the SPI as a slave and starting to send data to it. To avoid bus contention, the SPI system takes the

following actions:

1. The MSTR bit in SPCR is cleared and the SPI system becomes a slave. As a result of the SPI becoming a slave,

the MOSI and SCK pins become inputs.

2. The SPIF flag in SPSR is set, and if the SPI interrupt is enabled, and the I-bit in SREG is set, the interrupt routine

will be executed.

Thus, when interrupt-driven SPI transmission is used in master mode, and there exists a possibility that SS is driven low, the

interrupt should always check that the MSTR bit is still set. If the MSTR bit has been cleared by a slave select, it must be set

by the user to re-enable SPI master mode.

13.2.3 SPI Control Register – SPCR

• Bit 7 – SPIE: SPI Interrupt Enable

This bit causes the SPI interrupt to be executed if SPIF bit in the SPSR register is set and if the global interrupt enable bit in

SREG is set.

• Bit 6 – SPE: SPI Enable

When the SPE bit is written to one, the SPI is enabled. This bit must be set to enable any SPI operations.

• Bit 5 – DORD: Data Order

When the DORD bit is written to one, the LSB of the data word is transmitted first.

When the DORD bit is written to zero, the MSB of the data word is transmitted first.

• Bit 4 – MSTR: Master/Slave Select

This bit selects master SPI mode when written to one, and slave SPI mode when written logic zero. If SS is configured as an

input and is driven low while MSTR is set, MSTR will be cleared, and SPIF in SPSR will become set. The user will then have

to set MSTR to re-enable SPI master mode.

Bit 76543210

SPIE SPE DORD MSTR CPOL CPHA SPR1 SPR0 SPCR

Read/Write R/W R/W R/W R/W R/W R/W R/W R/W

Initial Value00000000

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• Bit 3 – CPOL: Clock Polarity

When this bit is written to one, SCK is high when idle. When CPOL is written to zero, SCK is low when idle. Refer to Figure

13-3 and Figure 13-4 for an example. The CPOL functionality is summarized below:

• Bit 2 – CPHA: Clock Phase

The settings of the clock phase bit (CPHA) determine if data is sampled on the leading (first) or trailing (last) edge of SCK.

Refer to Figure 13-3 and Figure 13-4 for an example. The CPOL functionality is summarized below:

• Bits 1, 0 – SPR1, SPR0: SPI Clock Rate Select 1 and 0

These two bits control the SCK rate of the device configured as a master. SPR1 and SPR0 have no effect on the slave. The

relationship between SCK and the clkIO frequency fclkio is shown in the following table:

13.2.4 SPI Status Register – SPSR

• Bit 7 – SPIF: SPI Interrupt Flag

When a serial transfer is complete, the SPIF flag is set. An interrupt is generated if SPIE in SPCR is set and global interrupts

are enabled. If SS is an input and is driven low when the SPI is in master mode, this will also set the SPIF flag. SPIF is

cleared by hardware when executing the corresponding interrupt handling vector. Alternatively, the SPIF bit is cleared by

first reading the SPI status register with SPIF set, then accessing the SPI data register (SPDR).

Table 13-2. CPOL Functionality

CPOL Leading Edge Trailing Edge

0Rising Falling

1Falling Rising

Table 13-3. CPHA Functionality

CPHA Leading Edge Trailing Edge

0Sample Setup

1Setup Sample

Table 13-4. Relationship Between SCK and the Oscillator Frequency

SPI2X SPR1 SPR0 SCK Frequency

0 0 0 fclkio/4

0 0 1 fclkio/16

0 1 0 fclkio/64

0 1 1 fclkio/128

1 0 0 fclkio/2

1 0 1 fclkio/8

1 1 0 fclkio/32

1 1 1 fclkio/64

Bit 76543210

SPIFWCOL–––––SPI2XSPSR

Read/Write R R R RRRRR/W

Initial Value00000000

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• Bit 6 – WCOL: Write COLlision Flag

The WCOL bit is set if the SPI data register (SPDR) is written during a data transfer. The WCOL bit (and the SPIF bit) are

cleared by first reading the SPI status register with WCOL set, and then accessing the SPI data register.

• Bit 5..1 – Res: Reserved Bits

These bits are reserved bits in the Atmel® ATtiny87/167 and will always read as zero.

• Bit 0 – SPI2X: Double SPI Speed Bit

When this bit is written logic one the SPI speed (SCK Frequency) will be doubled when the SPI is in master mode (see Table

13-4 on page 135). This means that the minimum SCK period will be two CPU clock periods. When the SPI is configured as

slave, the SPI is only guaranteed to work at fclkio/4 or lower.

The SPI interface on the Atmel ATtiny87/167 is also used for program memory and EEPROM downloading or uploading.

See Section 21.8 “Serial Downloading” on page 218 for serial programming and verification.

13.2.5 SPI Data Register – SPDR

• Bits 7:0 - SPD7:0: SPI Data

The SPI data register is a read/write register used for data transfer between the register file and the SPI shift register. Writing

to the register initiates data transmission. Reading the register causes the shift register receive buffer to be read.

13.3 Data Modes

There are four combinations of SCK phase and polarity with respect to serial data, which are determined by control bits

CPHA and CPOL. The SPI data transfer formats are shown in Figure 13-3 and Figure 13-4 on page 137. Data bits are

shifted out and latched in on opposite edges of the SCK signal, ensuring sufficient time for data signals to stabilize. This is

clearly seen by summarizing Table 13-2 and Table 13-3, as done below:

Bit 76543210

SPD7 SPD6 SPD5 SPD4 SPD3 SPD2 SPD1 SPD0 SPDR

Read/Write R/W R/W R/W R/W R/W R/W R/W R/W

Initial ValueXXXXXXXXUndefined

Table 13-5. CPOL Functionality

Leading Edge Trailing Edge SPI Mode

CPOL=0, CPHA=0 Sample (rising) Setup (falling) 0

CPOL=0, CPHA=1 Setup (rising) Sample (falling) 1

CPOL=1, CPHA=0 Sample (falling) Setup (rising) 2

CPOL=1, CPHA=1 Setup (falling) Sample (rising) 3

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Figure 13-3. SPI Transfer Format with CPHA = 0

Figure 13-4. SPI Transfer Format with CPHA = 1

LSB

MSB

Bit 1

Bit 6

Bit 2

Bit 5

Bit 3

Bit 4

Bit 3

Bit 5

Bit 2

Bit 6

Bit 1

MSB

LSB

MSB first (DORD = 0)

LSB first (DORD =1)

SCK (CPOL = 0)

mode 0

SCK (CPOL = 1)

mode 2

SAMPLE I

MOSI/MISO

CHANGE 0

MOSI PIN

CHANGE 0

MISO PIN

LSB

MSB

Bit 1

Bit 6

Bit 2

Bit 5

Bit 3

Bit 4

Bit 3

Bit 5

Bit 2

Bit 6

Bit 1

MSB

LSB

MSB first (DORD = 0)

LSB first (DORD =1)

SCK (CPOL = 0)

mode 1

SCK (CPOL = 1)

mode 3

SAMPLE I

MOSI/MISO

CHANGE 0

MOSI PIN

CHANGE 0

MISO PIN

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14. USI – Universal Serial Interface

14.1 Features

●Two-wire synchronous data transfer (master or slave)

●Three-wire synchronous data transfer (master or slave)

●Data received interrupt

●Wake up from idle mode

●In two-wire mode: Wake-up from all sleep modes, including power-down mode

●Two-wire start condition detector with interrupt capability

14.2 Overview

The universal serial interface, or USI, provides the basic hardware resources needed for serial communication. Combined

with a minimum of control software, the USI allows significantly higher transfer rates and uses less code space than

solutions based on software only. Interrupts are included to minimize the processor load.

A simplified block diagram of the USI is shown on Figure 14-1 for the actual placement of I/O pins, refer to Section 1.6 “Pin

Configuration” on page 6. CPU accessible I/O registers, including I/O bits and I/O pins, are shown in bold. The device-

specific I/O register and bit locations are listed in the Section 14.5 “Register Descriptions” on page 144.

Figure 14-1. Universal Serial Interface, Block Diagram

The 8-bit USI data register is directly accessible via the data bus and contains the incoming and outgoing data. The register

has no buffering so the data must be read as quickly as possible to ensure that no data is lost. The USI data register is a

serial shift register and the most significant bit that is the output of the serial shift register is connected to one of two output

pins depending of the wire mode configuration.

A transparent latch is inserted between the USI data register output and output pin, which delays the change of data output

to the opposite clock edge of the data input sampling. The serial input is always sampled from the data input (DI) pin

independent of the configuration.

USIDR

TIM0 COMP

USCK/ SCL

Two-wire Clock

Control Unit

CLOCK

HOLD

[1]

Bit0

Bit7

USISIF

USIOIF

USIPF

USIDC

USIDB

USISR

4-bit Counter

DI/ SDA

DO (Output only)

(Input/ Open Drain))

USISIE

USIOIE

USIWM1

USIWM0

USICS1

USICS0

USICLK

USITC

USICR

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The 4-bit counter can be both read and written via the data bus, and can generate an overflow interrupt. Both the USI data

register and the counter are clocked simultaneously by the same clock source. This allows the counter to count the number

of bits received or transmitted and generate an interrupt when the transfer is complete. Note that when an external clock

source is selected the counter counts both clock edges. In this case the counter counts the number of edges, and not the

number of bits. The clock can be selected from three different sources: The USCK pin, timer/counter0 compare match or

from software.

The Two-wire clock control unit can generate an interrupt when a start condition is detected on the two-wire bus. It can also

generate wait states by holding the clock pin low after a start condition is detected, or after the counter overflows.

14.3 Functional Descriptions

14.3.1 Three-wire Mode

The USI three-wire mode is compliant to the serial peripheral interface (SPI) mode 0 and 1, but does not have the slave

select (SS) pin functionality. However, this feature can be implemented in software if necessary. Pin names used by this

mode are: DI, DO, and USCK.

Figure 14-2. Three-wire Mode Operation, Simplified Diagram

Figure 14-2 shows two USI units operating in three-wire mode, one as master and one as slave. The two USI data register

are interconnected in such way that after eight USCK clocks, the data in each register are interchanged. The same clock

also increments the USI’s 4-bit counter. The counter overflow (interrupt) flag, or USIOIF, can therefore be used to determine

when a transfer is completed.

The clock is generated by the master device software by toggling the USCK pin via the PORT register or by writing a one to

the USITC bit in USICR.

Bit7 DI

USCK

PORTxn

SLAVE

Bit6 Bit5 Bit4 Bit3 Bit2 Bit1 Bit0

Bit7 DI

MASTER

Bit6 Bit5 Bit4 Bit3 Bit2 Bit1 Bit0

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Figure 14-3. Three-wire Mode, Timing Diagram

The three-wire mode timing is shown in Figure 14-3 at the top of the figure is a USCK cycle reference. One bit is shifted into

the USI data register (USIDR) for each of these cycles. The USCK timing is shown for both external clock modes. In external

clock mode 0 (USICS0 = 0), DI is sampled at positive edges, and DO is changed (data register is shifted by one) at negative

edges. External clock mode 1 (USICS0 = 1) uses the opposite edges versus mode 0, i.e., samples data at negative and

changes the output at positive edges. The USI clock modes corresponds to the SPI data mode 0 and 1.

Referring to the timing diagram (Figure 14-3), a bus transfer involves the following steps:

1. The slave device and master device sets up its data output and, depending on the protocol used, enables its out-

put driver (mark A and B). The output is set up by writing the data to be transmitted to the USI data register.

Enabling of the output is done by setting the corresponding bit in the port data direction register. Note that point A

and B does not have any specific order, but both must be at least one half USCK cycle before point C where the

data is sampled. This must be done to ensure that the data setup requirement is satisfied. The 4-bit counter is

reset to zero.

2. The master generates a clock pulse by software toggling the USCK line twice (C and D). The bit value on the

slave and master’s data input (DI) pin is sampled by the USI on the first edge (C), and the data output is changed

on the opposite edge (D). The 4-bit counter will count both edges.

3. Step 2. is repeated eight times for a complete register (byte) transfer.

4. After eight clock pulses (i.e., 16 clock edges) the counter will overflow and indicate that the transfer is completed.

The data bytes transferred must now be processed before a new transfer can be initiated. The overflow interrupt

will wake up the processor if it is set to idle mode. Depending of the protocol used the slave device can now set its

output to high impedance.

14.3.2 SPI Master Operation Example

The following code demonstrates how to use the USI module as a SPI master:

SPITransfer:

sts USIDR,r16

ldi r16,(1<<USIOIF)

sts USISR,r16

ldi r16,(1<<USIWM0)|(1<<USICS1)|(1<<USICLK)|(1<<USITC)

SPITransfer_loop:

sts USICR,r16

lds r16, USISR

sbrs r16, USIOIF

rjmp SPITransfer_loop

lds r16,USIDR

ret

6MSB 5 4 3 2 1 LSB

345678

6MSB

CYCLE

(Reference)

USCK

54321LSB

A B C D E

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The code is size optimized using only eight instructions (+ ret). The code example assumes that the DO and USCK pins are

enabled as output in the DDRA or DDRB register. The value stored in register r16 prior to the function is called is transferred

to the slave device, and when the transfer is completed the data received from the slave is stored back into the r16 register.

The second and third instructions clears the USI counter overflow flag and the USI counter value. The fourth and fifth

instruction set three-wire mode, positive edge shift register clock, count at USITC strobe, and toggle USCK. The loop is

repeated 16 times.

The following code demonstrates how to use the USI module as a SPI master with maximum speed (fsck = fck/4):

SPITransfer_Fast:

sts USIDR,r16

ldi r16,(1<<USIWM0)|(0<<USICS0)|(1<<USITC)

ldi r17,(1<<USIWM0)|(0<<USICS0)|(1<<USITC)|(1<<USICLK)

sts USICR,r16 ; MSB

sts USICR,r17

sts USICR,r16

sts USICR,r17

sts USICR,r16

sts USICR,r17

sts USICR,r16

sts USICR,r17

sts USICR,r16

sts USICR,r17

sts USICR,r16

sts USICR,r17

sts USICR,r16

sts USICR,r17

sts USICR,r16 ; LSB

sts USICR,r17

lds r16,USIDR

ret

14.3.3 SPI Slave Operation Example

The following code demonstrates how to use the USI module as a SPI slave:

init:

ldi r16,(1<<USIWM0)|(1<<USICS1)

sts USICR,r16

...

SlaveSPITransfer:

sts USIDR,r16

ldi r16,(1<<USIOIF)

sts USISR,r16

SlaveSPITransfer_loop:

lds r16, USISR

sbrs r16, USIOIF

rjmp SlaveSPITransfer_loop

lds r16,USIDR

ret

lull-In -—:I}“ i] —°\,— lull-In }’ 1 % AtmeL

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The code is size optimized using only eight instructions (+ ret). The code example assumes that the DO is configured as

output and USCK pin is configured as input in the DDR register. The value stored in register r16 prior to the function is called

is transferred to the master device, and when the transfer is completed the data received from the master is stored back into

the r16 register.

Note that the first two instructions is for initialization only and needs only to be executed once.These instructions sets three-

wire mode and positive edge USI data register clock. The loop is repeated until the USI counter overflow flag is set.

14.3.4 Two-wire Mode

The USI two-wire mode is compliant to the inter IC (TWI) bus protocol, but without slew rate limiting on outputs and input

noise filtering. Pin names used by this mode are SCL and SDA.

Figure 14-4. Two-wire Mode Operation, Simplified Diagram

Figure 14-4 shows two USI units operating in two-wire mode, one as master and one as slave. It is only the physical layer

that is shown since the system operation is highly dependent of the communication scheme used. The main differences

between the master and slave operation at this level, is the serial clock generation which is always done by the master, and

only the slave uses the clock control unit. Clock generation must be implemented in software, but the shift operation is done

automatically by both devices. Note that only clocking on negative edge for shifting data is of practical use in this mode. The

slave can insert wait states at start or end of transfer by forcing the SCL clock low. This means that the master must always

check if the SCL line was actually released after it has generated a positive edge.

Since the clock also increments the counter, a counter overflow can be used to indicate that the transfer is completed. The

clock is generated by the master by toggling the USCK pin via the PORT register.

The data direction is not given by the physical layer. A protocol, like the one used by the TWI-bus, must be implemented to

control the data flow.

Bit7

SDA

SCL

HOLD

SCL

SLAVE

Bit6 Bit5 Bit4 Bit3 Bit2 Bit1 Bit0

Two-wire

Clock

Control Unit

VCC

Bit7

SDA

SCL

MASTER

Bit6 Bit5 Bit4 Bit3 Bit2 Bit1 Bit0

PORTxn

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Figure 14-5. Two-wire Mode, Typical Timing Diagram

Referring to the timing diagram (Figure 14-5 on page 143), a bus transfer involves the following steps:

1. The a start condition is generated by the master by forcing the SDA low line while the SCL line is high (A). SDA

can be forced low either by writing a zero to bit 7 of the shift register, or by setting the corresponding bit in the

PORT register to zero. Note that the USI data register bit must be set to one for the output to be enabled. The

slave device’s start detector logic (Figure 14-6.) detects the start condition and sets the USISIF flag. The flag can

generate an interrupt if necessary.

2. In addition, the start detector will hold the SCL line low after the master has forced an negative edge on this line

(B). This allows the slave to wake up from sleep or complete its other tasks before setting up the USI data register

to receive the address. This is done by clearing the start condition flag and reset the counter.

3. The master set the first bit to be transferred and releases the SCL line (C). The slave samples the data and shift it

into the USI data register at the positive edge of the SCL clock.

4. After eight bits are transferred containing slave address and data direction (read or write), the slave counter over-

flows and the SCL line is forced low (D). If the slave is not the one the master has addressed, it releases the SCL

line and waits for a new start condition.

5. If the slave is addressed it holds the SDA line low during the acknowledgment cycle before holding the SCL line

low again (i.e., the counter register must be set to 14 before releasing SCL at (D)). Depending of the R/W bit the

master or slave enables its output. If the bit is set, a master read operation is in progress (i.e., the slave drives the

SDA line) The slave can hold the SCL line low after the acknowledge (E).

6. Multiple bytes can now be transmitted, all in same direction, until a stop condition is given by the master (F). Or a

new start condition is given.

If the slave is not able to receive more data it does not acknowledge the data byte it has last received. When the master does

a read operation it must terminate the operation by force the acknowledge bit low after the last byte transmitted.

Figure 14-6. Start Condition Detector, Logic Diagram

14.3.5 Start Condition Detector

The start condition detector is shown in Figure 14-6. The SDA line is delayed (in the range of 50 to 300 ns) to ensure valid

sampling of the SCL line. The start condition detector is only enabled in two-wire mode.

The start condition detector is working asynchronously and can therefore wake up the processor from the power-down sleep

mode. However, the protocol used might have restrictions on the SCL hold time. Therefore, when using this feature in this

case the oscillator start-up time set by the CKSEL fuses (see Section 4.1 “Clock Systems and their Distribution” on page 25)

must also be taken into the consideration. Refer to the USISIF bit description on page 145 for further details.

1 to 7 8

SADDRESS R/W ACK DATA ACK ACKDATA

1 to 8 9 1 to 8 99

A B C D E F

SDA

SCL

SDA

SCL

Write (USISIF)

CLR

USISIF

CLOCK

HOLD

CLR

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14.4 Alternative USI Usage

When the USI unit is not used for serial communication, it can be set up to do alternative tasks due to its flexible design.

14.4.1 Half-duplex Asynchronous Data Transfer

By utilizing the USI data register in three-wire mode, it is possible to implement a more compact and higher performance

UART than by software only.

14.4.2 4-bit Counter

The 4-bit counter can be used as a stand-alone counter with overflow interrupt. Note that if the counter is clocked externally,

both clock edges will generate an increment.

14.4.3 12-bit Timer/Counter

Combining the USI 4-bit counter and timer/counter0 allows them to be used as a 12-bit counter.

14.4.4 Edge Triggered External Interrupt

By setting the counter to maximum value (F) it can function as an additional external interrupt. The overflow flag and interrupt

enable bit are then used for the external interrupt. This feature is selected by the USICS1 bit.

14.4.5 Software Interrupt

The counter overflow interrupt can be used as a software interrupt triggered by a clock strobe.

14.5 Register Descriptions

14.5.1 USIDR – USI Data Register

• Bits 7:0 – USID7..0: USI Data

When accessing the USI data register (USIDR) the serial register can be accessed directly. If a serial clock occurs at the

same cycle the register is written, the register will contain the value written and no shift is performed. A (left) shift operation is

performed depending of the USICS1..0 bits setting. The shift operation can be controlled by an external clock edge, by a

timer/counter0 compare match, or directly by software using the USICLK strobe bit. Note that even when no wire mode is

selected (USIWM1..0 = 0) both the external data input (DI/SDA) and the external clock input (USCK/SCL) can still be used

by the USI data register.

The output pin in use, DO or SDA depending on the wire mode, is connected via the output latch to the most significant bit

(bit 7) of the data register. The output latch is open (transparent) during the first half of a serial clock cycle when an external

clock source is selected (USICS1 = 1), and constantly open when an internal clock source is used (USICS1 = 0). The output

will be changed immediately when a new MSB written as long as the latch is open. The latch ensures that data input is

sampled and data output is changed on opposite clock edges.

Note that the corresponding data direction register to the pin must be set to one for enabling data output from the USI data

Bit 7 6 5 4 3 2 1 0

USID7 USID6 USID5 USID4 USID3 USID2 USID1 USID0 USIDR

Read/Write R/W R/W R/W R/W R/W R/W R/W R/W

Initial Value 0 0 0 0 0 0 0 0

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14.5.2 USIBR – USI Buffer Register

• Bits 7:0 – USID7..0: USI Buffer

The content of the serial register is loaded to the USI buffer register when the transfer is completed, and instead of

accessing the USI data register (the serial register) the USI data buffer can be accessed when the CPU reads the received

data. This gives the CPU time to handle other program tasks too as the controlling of the USI is not so timing critical. The USI

flags as set same as when reading the USIDR register.

14.5.3 USISR – USI Status Register

The Status Register contains Interrupt Flags, line Status Flags and the counter value.

• Bit 7 – USISIF: Start Condition Interrupt Flag

When two-wire mode is selected, the USISIF flag is set (to one) when a start condition is detected. When output disable

mode or three-wire mode is selected and (USICSx = 11b & USICLK = 0) or (USICS = 10b & USICLK = 0), any edge on the

SCK pin sets the flag.

An interrupt will be generated when the flag is set while the USISIE bit in USICR and the global interrupt enable flag are set.

The flag will only be cleared by writing a logical one to the USISIF bit. Clearing this bit will release the start detection hold of

USCL in two-wire mode.

A start condition interrupt will wake up the processor from all sleep modes.

• Bit 6 – USIOIF: Counter Overflow Interrupt Flag

This flag is set (one) when the 4-bit counter overflows (i.e., at the transition from 15 to 0). An interrupt will be generated when

the flag is set while the USIOIE bit in USICR and the global interrupt enable flag are set. The flag will only be cleared if a one

is written to the USIOIF bit. Clearing this bit will release the counter overflow hold of SCL in two-wire mode.

A counter overflow interrupt will wake up the processor from idle sleep mode.

• Bit 5 – USIPF: Stop Condition Flag

When two-wire mode is selected, the USIPF flag is set (one) when a stop condition is detected. The flag is cleared by writing

a one to this bit. Note that this is not an interrupt flag. This signal is useful when implementing two-wire bus master

arbitration.

• Bit 4 – USIDC: Data Output Collision

This bit is logical one when bit 7 in the USI data register differs from the physical pin value. The flag is only valid when two-

wire mode is used. This signal is useful when implementing two-wire bus master arbitration

Bit 7 6 5 4 3 2 1 0

USIB7 USIB6 USIB5 USIB4 USIB3 USIB2 USIB1 USIB0 USIBR

Read/Write R R R R R R R R

Initial Value 0 0 0 0 0 0 0 0

Bit 7 6 5 4 3 2 1 0

USISIF USIOIF USIPF USIDC USICNT3 USICNT2 USICNT1 USICNT0 USISR

Read/Write R/W R/W R/W R R/W R/W R/W R/W

Initial Value 0 0 0 0 0 0 0 0

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• Bits 3:0 – USICNT3..0: Counter Value

These bits reflect the current 4-bit counter value. The 4-bit counter value can directly be read or written by the CPU.

The 4-bit counter increments by one for each clock generated either by the external clock edge detector, by a timer/counter0

compare match, or by software using USICLK or USITC strobe bits. The clock source depends of the setting of the

USICS1..0 bits. For external clock operation a special feature is added that allows the clock to be generated by writing to the

USITC strobe bit. This feature is enabled by write a one to the USICLK bit while setting an external clock source

(USICS1 = 1).

Note that even when no wire mode is selected (USIWM1..0 = 0) the external clock input (USCK/SCL) are can still be used by

the counter.

14.5.4 USICR – USI Control Register

The control register includes interrupt enable control, wire mode setting, clock select setting, and clock strobe.

• Bit 7 – USISIE: Start Condition Interrupt Enable

Setting this bit to one enables the start condition detector interrupt. If there is a pending interrupt when the USISIE and the

global interrupt enable flag is set to one, this will immediately be executed. Refer to the USISIF bit description on page 145

for further details.

• Bit 6 – USIOIE: Counter Overflow Interrupt Enable

Setting this bit to one enables the counter overflow interrupt. If there is a pending interrupt when the USIOIE and the global

interrupt enable flag is set to one, this will immediately be executed. Refer to the USIOIF bit description on page 145 for

further details.

• Bit 5:4 – USIWM1:0: Wire Mode

These bits set the type of wire mode to be used. Basically only the function of the outputs are affected by these bits. Data

and clock inputs are not affected by the mode selected and will always have the same function. The counter and USI data

between USIWM1:0 and the USI operation is summarized in Table 14-1 on page 147.

Bit 7 6 5 4 3 2 1 0

USISIE USIOIE USIWM1 USIWM0 USICS1 USICS0 USICLK USITC USICR

Read/Write R/W R/W R/W R/W R/W R/W W W

Initial Value 0 0 0 0 0 0 0 0

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• Bit 3:2 – USICS1:0: Clock Source Select

These bits set the clock source for the USI data register and counter. The data output latch ensures that the output is

changed at the opposite edge of the sampling of the data input (DI/SDA) when using external clock source (USCK/SCL).

When software strobe or timer/counter0 compare match clock option is selected, the output latch is transparent and

therefore the output is changed immediately. Clearing the USICS1:0 bits enables software strobe option. When using this

option, writing a one to the USICLK bit clocks both the USI data register and the counter. For external clock source

(USICS1 = 1), the USICLK bit is no longer used as a strobe, but selects between external clocking and software clocking by

the USITC strobe bit.

Table 14-2 on page 148 shows the relationship between the USICS1..0 and USICLK setting and clock source used for the

USI data register and the 4-bit counter.

Table 14-1. Relations between USIWM1..0 and the USI Operation

USIWM1 USIWM0 Description

0 0 Outputs, clock hold, and start detector disabled. Port pins operates as normal.

0 1

Three-wire mode. Uses DO, DI, and USCK pins.

The data output (DO) pin overrides the corresponding bit in the PORT register in this mode.

However, the corresponding DDR bit still controls the data direction. When the port pin is set as

input the pins pull-up is controlled by the PORT bit.

The data input (DI) and serial clock (USCK) pins do not affect the normal port operation. When

operating as master, clock pulses are software generated by toggling the PORT register, while

the data direction is set to output. The USITC bit in the USICR register can be used for this

purpose.

1 0

Two-wire mode. Uses SDA (DI) and SCL (USCK) pins(1).

The serial data (SDA) and the serial clock (SCL) pins are bi-directional and uses open-collector

output drives. The output drivers are enabled by setting the corresponding bit for SDA and SCL

in the DDR register.

When the output driver is enabled for the SDA pin, the output driver will force the line SDA low

if the output of the USI data register or the corresponding bit in the PORT register is zero.

Otherwise the SDA line will not be driven (i.e., it is released). When the SCL pin output driver is

enabled the SCL line will be forced low if the corresponding bit in the PORT register is zero, or

by the start detector. Otherwise the SCL line will not be driven.

The SCL line is held low when a start detector detects a start condition and the output is

enabled. Clearing the start condition flag (USISIF) releases the line. The SDA and SCL pin

inputs is not affected by enabling this mode. Pull-ups on the SDA and SCL port pin are disabled

in Two-wire mode.

1 1

Two-wire mode. Uses SDA and SCL pins.

Same operation as for the two-wire mode described above, except that the SCL line is also

held low when a counter overflow occurs, and is held low until the counter overflow flag

(USIOIF) is cleared.

Note: 1. The DI and USCK pins are renamed to serial data (SDA) and serial clock (SCL) respectively to avoid confu-

sion between the modes of operation.

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• Bit 1 – USICLK: Clock Strobe

Writing a one to this bit location strobes the USI data register to shift one step and the counter to increment by one, provided

that the USICS1..0 bits are set to zero and by doing so the software clock strobe option is selected. The output will change

immediately when the clock strobe is executed, i.e., in the same instruction cycle. The value shifted into the USI data register

is sampled the previous instruction cycle. The bit will be read as zero.

When an external clock source is selected (USICS1 = 1), the USICLK function is changed from a clock strobe to a clock

select register. Setting the USICLK bit in this case will select the USITC strobe bit as clock source for the 4-bit counter (see

Table 14-2).

• Bit 0 – USITC: Toggle Clock Port Pin

Writing a one to this bit location toggles the USCK/SCL value either from 0 to 1, or from 1 to 0. The toggling is independent

of the setting in the data direction register, but if the PORT value is to be shown on the pin the DDB2 must be set as output

(to one). This feature allows easy clock generation when implementing master devices. The bit will be read as zero.

When an external clock source is selected (USICS1 = 1) and the USICLK bit is set to one, writing to the USITC strobe bit will

directly clock the 4-bit counter. This allows an early detection of when the transfer is done when operating as a master

device.

14.5.5 USIPP – USI Pin Position

• Bits 7:1 – Res: Reserved Bits

These bits are reserved bits in the Atmel® ATtiny87/167 and always reads as zero.

• Bit 0 – USIPOS: USI Pin Position

Setting or clearing this bit changes the USI pin position.

Table 14-2. Relations between the USICS1..0 and USICLK Setting

USICS1 USICS0 USICLK USI Data Register Clock Source 4-bit Counter Clock Source

0 0 0 No Clock No Clock

0 0 1 Software clock strobe (USICLK) Software clock strobe (USICLK)

0 1 X Timer/counter0 compare match Timer/counter0 compare match

1 0 0 External, positive edge External, both edges

1 1 0 External, negative edge External, both edges

1 0 1 External, positive edge Software clock strobe (USITC)

1 1 1 External, negative edge Software clock strobe (USITC)

Bit 76543210

-------USIPOSUSIPP

Read/Write R R R RRRRR/W

Initial Value00000000

Table 14-3. USI Pin Position

USIPOS USI Pin Position

0PortB

(Default)

DI, SDA PB0 - (PCINT8/OC1AU)

DO PB1 - (PCINT9/OC1BU)

USCK, SCL PB2 - (PCINT10/OC1AV)

1Port A

(Alternate)

DI, SDA PA4 - (PCINT4/ADC4/ICP1/MOSI)

DO PA2 - (PCINT2/ADC2/OC0A/MISO)

USCK, SCL PA5 - (PCINT5/ADC5/T1/SCK)

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15. LIN/UART - Local Interconnect Network Controller or UART

The LIN (local interconnect network) is a serial communications protocol which efficiently supports the control of

mechatronics nodes in distributed automotive applications. The main properties of the LIN bus are:

●Single master with multiple slaves concept

●Low cost silicon implementation based on common UART/SCI interface

●Self synchronization with on-chip oscillator in slave node

●Deterministic signal transmission with signal propagation time computable in advance

●Low cost single-wire implementation

●Speed up to 20Kbit/s.

LIN provides a cost efficient bus communication where the bandwidth and versatility of CAN are not required. The

specification of the line driver/receiver needs to match the ISO9141 NRZ-standard.

If LIN is not required, the controller alternatively can be programmed as universal asynchronous serial receiver and

transmitter (UART).

15.1 LIN Features

●Hardware implementation of LIN 2.1 (LIN 1.3 compatibility)

●Small, CPU efficient and independent master/slave routines based on “LIN Work Flow Concept” of LIN 2.1

specification

●Automatic LIN header handling and filtering of irrelevant LIN frames

●Automatic LIN response handling

●Extended LIN error detection and signaling

●Hardware frame time-out detection

●“Break-in-data” support capability

●Automatic re-synchronization to ensure proper frame integrity

●Fully flexible extended frames support capabilities

15.2 UART Features

●Full duplex operation (independent serial receive and transmit processes)

●Asynchronous operation

●High resolution baud rate generator

●Hardware support of 8 data bits, odd/even/no parity Bit, 1 stop bit frames

●Data over-run and framing error detection

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15.3 LIN Protocol

15.3.1 Master and Slave

A LIN cluster consists of one master task and several slave tasks. A master node contains the master task as well as a slave

task. All other nodes contain a slave task only.

Figure 15-1. LIN Cluster with One Master Node and “n” Slave Nodes

The master task decides when and which frame shall be transferred on the bus. The slave tasks provide the data

transported by each frame. Both the master task and the slave task are parts of the frame handler

15.3.2 Frames

A frame consists of a header (provided by the master task) and a response (provided by a slave task).

The header consists of a BREAK and SYNC pattern followed by a PROTECTED IDENTIFIER. The identifier uniquely

defines the purpose of the frame. The slave task appointed for providing the response associated with the identifier transmits

it. The response consists of a DATA field and a CHECKSUM field.

Figure 15-2. Master and Slave Tasks Behavior in LIN Frame

The slave tasks waiting for the data associated with the identifier receives the response and uses the data transported after

verifying the checksum.

Figure 15-3. Structure of a LIN Frame

15.3.3 Data Transport

Two types of data may be transported in a frame; signals or diagnostic messages.

●Signals

Signals are scalar values or byte arrays that are packed into the data field of a frame. A signal is always present at the

same position in the data field for all frames with the same identifier.

●Diagnostic messages

Diagnostic messages are transported in frames with two reserved identifiers. The interpretation of the data field

depends on the data field itself as well as the state of the communicating nodes.

master task

slave task

master node

slave task

slave node

slave task

slave node

LIN bus

HEADER

Master Task

Slave Task 1

Slave Task 2

RESPONSE

HEADER

RESPONSE

Field Field

SYNC

HEADER

FRAME SLOT

RESPONSE

Break Delimiter

BREAK

Field

PROTECTED

IDENTIFIER

Field

DATA 0

Field

DATA n CHECKSUM

Field

Inter-byte space Inter-frame space

Each byte field is transmitted as a serial byte, LSB first

Response Space

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15.3.4 Schedule Table

The master task (in the master node) transmits frame headers based on a schedule table. The schedule table specifies the

identifiers for each header and the interval between the start of a frame and the start of the following frame. The master

application may use different schedule tables and select among them.

15.3.5 Compatibility with LIN 1.3

LIN 2.1 is a super-set of LIN 1.3.

A LIN 2.1 master node can handle clusters consisting of both LIN 1.3 slaves and/or LIN 2.1 slaves. The master will then

avoid requesting the new LIN 2.1 features from a LIN 1.3 slave:

●Enhanced checksum,

●Re-configuration and diagnostics,

●Automatic baud rate detection,

●“Response error” status monitoring.

LIN 2.1 slave nodes can not operate with a LIN 1.3 master node (e.g. the LIN1.3 master does not support the enhanced

checksum).

The LIN 2.1 physical layer is backwards compatible with the LIN1.3 physical layer. But not the other way around. The LIN 2.1

physical layer sets greater requirements, i.e. a master node using the LIN 2.1 physical layer can operate in a LIN 1.3 cluster.

15.4 LIN/UART Controller

The LIN/UART controller is divided in three main functions:

●Tx LIN header function,

●Rx LIN header function,

●LIN response function.

These functions mainly use two services:

●Rx service,

●Tx service.

Because these two services are basically UART services, the controller is also able to switch into an UART function.

15.4.1 LIN Overview

The LIN/UART controller is designed to match as closely as possible to the LIN software application structure. The LIN

software application is developed as independent tasks, several slave tasks and one master task (c.f. Section 15.3.4

“Schedule Table” on page 151). The Atmel® ATtiny87/167 conforms to this perspective. The only link between the master

task and the slave task will be at the cross-over point where the interrupt routine is called once a new identifier is available.

Thus, in a master node, housing both master and slave task, the Tx LIN header function will alert the slave task of an

identifier presence. In the same way, in a slave node, the Rx LIN header function will alert the slave task of an identifier

presence.

When the slave task is warned of an identifier presence, it has first to analyze it to know what to do with the response.

Hardware flags identify the presence of one of the specific identifiers from 60 (0x3C) up to 63 (0x3F).

For LIN communication, only four interrupts need to be managed:

●LIDOK: New LIN identifier available,

●LRXOK: LIN response received,

●LTXOK: LIN response transmitted,

●LERR: LIN error(s).

The wake-up management can be automated using the UART wake-up capability and a node sending a minimum of 5 low

bits (0xF0) for LIN 2.1 and 8 low bits (0x80) for LIN 1.3. Pin change interrupt on LIN wake-up signal can be also used to exit

the device of one of its sleep modes.

Extended frame identifiers 62 (0x3E) and 63 (0x3F) are reserved to allow the embedding of user-defined message formats

and future LIN formats. The byte transfer mode offered by the UART will ensure the upwards compatibility of LIN slaves with

accommodation of the LIN protocol.

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15.4.2 UART Overview

The LIN/UART controller can also function as a conventional UART. By default, the UART operates as a full duplex

controller. It has local loop back circuitry for test purposes. The UART has the ability to buffer one character for transmit and

two for receive. The receive buffer is made of one 8-bit serial register followed by one 8-bit independent buffer register.

Automatic flag management is implemented when the application puts or gets characters, thus reducing the software

overhead. Because transmit and receive services are independent, the user can save one device pin when one of the two

services is not used. The UART has an enhanced baud rate generator providing a maximum error of 2% whatever the clock

frequency and the targeted baud rate.

15.4.3 LIN/UART Controller Structure

Figure 15-4. LIN/UART Controller Block Diagram

Prescaler

clkI/O

RxD

Sample /bit BAUD_RATE

Get Byte

RX Frame Time out

Synchronization

Monitoring

Data FIFO

Put Byte

Finite State Machine

FSM

BUFFER

Tx Response Rx Response x Header or LIN Anon AtmeL

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15.4.4 LIN/UART Command Overview

Figure 15-5. LIN/UART Command Dependencies

Table 15-1. LIN/UART Command List

LENA LCMD[2] LCMD[1] LCMD[0] Command Comment

0 x x x Disable peripheral

00Rx Header - LIN Abort LIN Withdrawal

1Tx Header LCMD[2..0]=000 after Tx

10Rx Response LCMD[2..0]=000 after Rx

1Tx Response LCMD[2..0]=000 after Tx

0 0 Byte transfer

no CRC, no Time out

LTXDL=LRXDL=0

(LINDLR: read only register)

1 0 Rx Byte

0 1 Tx Byte

1 1 Full duplex

Rx Header

LIN Abort

Byte

Transfer

DISABLE

LIN

UART

Response

IDOK

Recommended

Way

TXOK

RXOK

Byte

Response

Byte

Header

Full

Duplex

Possible

Way

Automatic

Return

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15.4.5 Enable/Disable

Setting the LENA bit in LINCR register enables the LIN/UART controller. To disable the LIN/UART controller, LENA bit must

be written to 0. No wait states are implemented, so, the disable command is taken into account immediately.

15.4.6 LIN Commands

Clearing the LCMD[2] bit in LINCR register enables LIN commands.

As shown in Table 15-1 on page 153, four functions controlled by the LCMD[1..0] bits of LINCR register are available (c.f.

Figure 15-5 on page 153).

15.4.6.1 Rx Header / LIN Abort Function

This function (or state) is mainly the withdrawal mode of the controller.

When the controller has to execute a master task, this state is the start point before enabling a Tx header command.

When the controller has only to execute slave tasks, LIN header detection/acquisition is enabled as background function. At

the end of such an acquisition (Rx header function), automatically the appropriate flags are set, and in LIN 1.3, the LINDLR

This state is also the start point before enabling the Tx or the Rx response command.

A running function (i.e. Tx header, Tx or Rx response ) can be aborted by clearing LCMD[1..0] bits in LINCR register (see

Section 15.5.11 “Break-in-data” on page 163). In this case, an abort flag - LABORT - in LINERR register will be set to inform

the other software tasks. No wait states are implemented, so, the abort command is taken into account immediately.

Rx Header function is responsible for:

●The BREAK field detection,

●The hardware re-synchronization analyzing the SYNCH field,

●The reception of the PROTECTED IDENTIFIER field, the parity control and the update of the LINDLR register in case

of LIN 1.3,

●The starting of the frame_time_out,

●The checking of the LIN communication integrity.

15.4.6.2 Tx Header Function

In accordance with the LIN protocol, only the master task must enable this function. The header is sent in the appropriate

timed slots at the programmed baud rate (c.f. LINBRR & LINBTR registers).

The controller is responsible for:

●The transmission of the BREAK field - 13 dominant bits,

●The transmission of the SYNCH field - character 0x55,

●The transmission of the PROTECTED IDENTIFIER field. It is the full content of the LINIDR register (automatic check

bits included).

At the end of this transmission, the controller automatically returns to Rx header / LIN abort state (i.e. LCMD[1..0] = 00) after

setting the appropriate flags. This function leaves the controller in the same setting as after the Rx header function. This

means that, in LIN 1.3, the LINDLR register is set with the uncoded length value at the end of the Tx header function.

During this function, the controller is also responsible for:

●The starting of the Frame_Time_Out,

●The checking of the LIN communication integrity.

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15.4.6.3 Rx and TX Response Functions

These functions are initiated by the slave task of a LIN node. They must be used after sending an header (master task) or

after receiving an header (considered as belonging to the slave task). When the TX response order is sent, the transmission

begins. A Rx response order can be sent up to the reception of the last serial bit of the first byte (before the stop-bit).

In LIN 1.3, the header slot configures the LINDLR register. In LIN 2.1, the user must configure the LINDLR register, either

LRXDL[3..0] for Rx response either LTXDL[3..0] for Tx response.

When the command starts, the controller checks the LIN13 bit of the LINCR register to apply the right rule for computing the

checksum. Checksum calculation over the DATA bytes and the PROTECTED IDENTIFIER byte is called enhanced

checksum and it is used for communication with LIN 2.1 slaves. Checksum calculation over the DATA bytes only is called

classic checksum and it is used for communication with LIN 1.3 slaves. Note that identifiers 60 (0x3C) to 63 (0x3F) shall

always use classic checksum.

At the end of this reception or transmission, the controller automatically returns to Rx header / LIN abort state (i.e.

LCMD[1..0] = 00) after setting the appropriate flags.

If an LIN error occurs, the reception or the transmission is stopped, the appropriate flags are set and the LIN bus is left to

recessive state.

During these functions, the controller is responsible for:

●The initialization of the checksum operator,

●The transmission or the reception of ‘n’ data with the update of the checksum calculation,

●The transmission or the checking of the CHECKSUM field,

●The checking of the frame_time_out,

●The checking of the LIN communication integrity.

While the controller is sending or receiving a response, BREAK and SYNCH fields can be detected and the identifier of this

new header will be recorded. Of course, specific errors on the previous response will be maintained with this identifier

reception.

15.4.6.4 Handling Data of LIN response

A FIFO data buffer is used for data of the LIN response. After setting all parameters in the LINSEL register, repeated

accesses to the LINDAT register perform data read or data write (c.f. Section 15.5.15 “Data Management” on page 164).

Note that LRXDL[3..0] and LTXDL[3..0] are not linked to the data access.

15.4.7 UART Commands

Setting the LCMD[2] bit in LINENR register enables UART commands.

Tx byte and Rx byte services are independent as shown in Table 15-1 on page 153.

●Byte transfer: the UART is selected but both Rx and Tx services are disabled,

●Rx byte: only the Rx service is enable but Tx service is disabled,

●Tx byte: only the Tx service is enable but Rx service is disabled,

●Full duplex: the UART is selected and both Rx and Tx services are enabled.

This combination of services is controlled by the LCMD[1..0] bits of LINENR register (c.f. Figure 15-5 on page 153).

15.4.7.1 Data Handling

The FIFO used for LIN communication is disabled during UART accesses. LRXDL[3..0] and LTXDL[3..0] values of LINDLR

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15.4.7.2 Rx Service

Once this service is enabled, the user is warned of an in-coming character by the LRXOK flag of LINSIR register. Reading

LINDAT register automatically clears the flag and makes free the second stage of the buffer. If the user considers that the in-

coming character is irrelevant without reading it, he directly can clear the flag (see specific flag management described in

Section 15.6.2 “LIN Status and Interrupt Register - LINSIR” on page 167).

The intrinsic structure of the Rx service offers a 2-byte buffer. The fist one is used for serial to parallel conversion, the

second one receives the result of the conversion. This second buffer byte is reached reading LINDAT register. If the 2-byte

buffer is full, a new in-coming character will overwrite the second one already recorded. An OVRERR error in

LINERR register will then accompany this character when read.

A FERR error in LINERR register will be set in case of framing error.

15.4.7.3 Tx Service

If this service is enabled, the user sends a character by writing in LINDAT register. Automatically the LTXOK flag of

LINSIR register is cleared. It will rise at the end of the serial transmission. If no new character has to be sent, LTXOK flag

can be cleared separately (see specific flag management described in Section 15.6.2 “LIN Status and Interrupt Register -

LINSIR” on page 167).

There is no transmit buffering.

No error is detected by this service.

15.5 LIN/UART Description

15.5.1 Reset

The AVR® core reset logic signal also resets the LIN/UART controller. Another form of reset exists, a software reset

controlled by LSWRES bit in LINCR register. This self-reset bit performs a partial reset as shown in Table 15-2.

15.5.2 Clock

The I/O clock signal (clki/o) also clocks the LIN/UART controller. It is its unique clock.

15.5.3 LIN Protocol Selection

LIN13 bit in LINCR register is used to select the LIN protocol:

●LIN13 = 0 (default): LIN 2.1 protocol,

●LIN13 = 1: LIN 1.3 protocol.

The controller checks the LIN13 bit in computing the checksum (enhanced checksum in LIN2.1 / classic checksum in LIN

1.3). This bit is irrelevant for UART commands.

Table 15-2. Reset of LIN/UART Registers

LIN control reg. LINCR 0000 0000 b0000 0000 b

x=unknown

u=unchanged

LIN status & interrupt reg. LINSIR 0000 0000 b0000 0000 b

LIN enable interrupt reg. LINENIR 0000 0000 bxxxx 0000 b

LIN error reg. LINERR 0000 0000 b0000 0000 b

LIN bit timing reg. LINBTR 0010 0000 b0010 0000 b

LIN baud rate reg. low LINBRRL 0000 0000 buuuu uuuu b

LIN baud rate reg. high LINBRRH 0000 0000 bxxxx uuuu b

LIN data length reg. LINDLR 0000 0000 b0000 0000 b

LIN identifier reg. LINIDR 1000 0000 b1000 0000 b

LIN data buffer selection LINSEL 0000 0000 bxxxx 0000 b

LIN data LINDAT 0000 0000 b0000 0000 b

J | Jr J |

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15.5.4 Configuration

Depending on the mode (LIN or UART), LCONF[1..0] bits of the LINCR register set the controller in the following

configuration (see Table 15-3).

The LIN configuration is independent of the programmed LIN protocol.

The listening mode connects the internal Tx LIN and the internal Rx LIN together. In this mode, the TXLIN output pin is

disabled and the RXLIN input pin is always enabled. The same scheme is available in UART mode.

Figure 15-6. Listening Mode

15.5.5 Busy Signal

LBUSY bit flag in LINSIR register is the image of the BUSY signal. It is set and cleared by hardware. It signals that the

controller is busy with LIN or UART communication.

15.5.5.1 Busy Signal in LIN Mode

Figure 15-7. Busy Signal in LIN Mode

Table 15-3. Configuration Table versus Mode

Mode LCONF[1..0] Configuration

LIN

00 bLIN standard configuration (default)

01 bNo CRC field detection or transmission

10 bFrame_time_out disable

11 bListening mode

UART

00 b8-bit data, no parity and 1 stop-bit

01 b8-bit data, even parity and 1 stop-bit

10 b8-bit data, odd parity and 1 stop-bit

11 bListening mode, 8-bit data, no parity and 1 stop-bit

TXLIN

internal

Tx LIN

internal

Rx LIN

LISTEN

RXLIN

Field Field

SYNC

Node providing the master task

Node providing a slave task

HEADER

LIN Bus

1) LBUSY

2) LBUSY

3) LBUSY

FRAME SLOT

RESPONSE

LCMD = Tx Header LIDOK LCMD = Tx or Rx Response LTXOK or LRXOK

BREAK

Field

PROTECTED

IDENTIFIER

Field

DATA-0

Field

DATA-n CHECKSUM

Field

Node providing neither the master task, neither a slave task

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When the busy signal is set, some registers are locked, user writing is not allowed:

●“LIN control register” - LINCR - except LCMD[2..0], LENA and LSWRES,

●“LIN baud rate registers” - LINBRRL and LINBRRH,

●“LIN data length register” - LINDLR,

●“LIN identifier register” - LINIDR,

●“LIN data register” - LINDAT.

If the busy signal is set, the only available commands are:

●LCMD[1..0] = 00 b, the abort command is taken into account at the end of the byte,

●LENA = 0 and/or LCMD[2] = 0, the kill command is taken into account immediately,

●LSWRES = 1, the reset command is taken into account immediately.

Note that, if another command is entered during busy signal, the new command is not validated and the LOVRERR bit flag of

the LINERR register is set. The on-going transfer is not interrupted.

15.5.5.2 Busy Signal in UART Mode

During the byte transmission, the busy signal is set. This locks some registers from being written:

●“LIN control register” - LINCR - except LCMD[2..0], LENA and LSWRES,

●“LIN data register” - LINDAT.

The busy signal is not generated during a byte reception.

15.5.6 Bit Timing

15.5.6.1 Baud rate Generator

The baud rate is defined to be the transfer rate in bits per second (bps):

●BAUD: Baud rate (in bps),

●fclki/o: System I/O clock frequency,

●LDIV[11..0]: Contents of LINBRRH & LINBRRL registers - (0-4095), the pre-scaler receives clki/o as input clock.

●LBT[5..0]: Least significant bits of - LINBTR register- (0-63) is the number of samplings in a LIN or UART bit (default

value 32).

Equation for calculating baud rate:

BAUD = fclki/o / LBT[5..0] x (LDIV[11..0] + 1)

Equation for setting LINDIV value:

LDIV[11..0] = ( fclki/o / LBT[5..0] x BAUD ) - 1

Note that in reception a majority vote on three samplings is made.

15.5.6.2 Re-synchronization in LIN Mode

When waiting for Rx header, LBT[5..0] = 32 in LINBTR register. The re-synchronization begins when the BREAK is detected.

If the BREAK size is not in the range (10.5 bits min., 28 bits max. — 13 bits nominal), the BREAK is refused. The re-

synchronization is done by adjusting LBT[5..0] value to the SYNCH field of the received header (0x55). Then the

PROTECTED IDENTIFIER is sampled using the new value of LBT[5..0].

The re-synchronization implemented in the controller tolerates a clock deviation of ±20% and adjusts the baud rate in a ±2%

range.

The new LBT[5..0] value will be used up to the end of the response. Then, the LBT[5..0] will be reset to 32 for the next

header.

The LINBTR register can be used to (software) re-calibrate the clock oscillator.

The re-synchronization is not performed if the LIN node is enabled as a master.

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15.5.6.3 Handling LBT[5..0]

LDISR bit of LINBTR register is used to:

●Disable the re-synchronization (for instance in the case of LIN MASTER node),

●To enable the setting of LBT[5..0] (to manually adjust the baud rate especially in the case of UART mode). A minimum

of 8 is required for LBT[5..0] due to the sampling operation.

Note that the LENA bit of LINCR register is important for this handling (see Figure 15-8).

Figure 15-8. Handling LBT[5..0]

15.5.7 Data Length

Section 15.4.6 “LIN Commands” on page 154 describes how to set or how are automatically set the LRXDL[3..0] or

LTXDL[3..0] fields of LINDLR register before receiving or transmitting a response.

In the case of Tx response the LRXDL[3..0] will be used by the hardware to count the number of bytes already successfully

sent.

In the case of Rx response the LTXDL[3..0] will be used by the hardware to count the number of bytes already successfully

received.

If an error occurs, this information is useful to the programmer to recover the LIN messages.

15.5.7.1 Data Length in LIN 2.1

●If LTXDL[3..0]=0 only the CHECKSUM will be sent,

●If LRXDL[3..0]=0 the first byte received will be interpreted as the CHECKSUM,

●If LTXDL[3..0] or LRXDL[3..0] >8, values will be forced to 8 after the command setting and before sending or receiving

of the first byte.

LENA ?

(LINCR bit4)

LDISR

to write

= 1

= 0

Write in LINBTR register

LBT [5..0] forced to 0x20

LDISR forced to 0

Enable re-synch. in LIN mode

LBT [5..0] = LBT [5..0] to write

(LBT [5..0]

min

= 8)

LDISR forced to 1

Disable re-synch. in LIN mode

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15.5.7.2 Data Length in LIN 1.3

●LRXDL and LTXDL fields are both hardware updated before setting LIDOK by decoding the data length code

contained in the received PROTECTED IDENTIFIER (LRXDL = LTXDL).

●Via the above mechanism, a length of 0 or >8 is not possible.

15.5.7.3 Data Length in Rx Response

Figure 15-9. LIN2.1 - Rx Response - No error

●The user initializes LRXDL field before setting the Rx response command,

●After setting the Rx response command, LTXDL is reset by hardware,

●LRXDL field will remain unchanged during Rx (during busy signal),

●LTXDL field will count the number of received bytes (during busy signal),

●If an error occurs, Rx stops, the corresponding error flag is set and LTXDL will give the number of received bytes

without error,

●If no error occurs, LRXOK is set after the reception of the CHECKSUM, LRXDL will be unchanged (and

LTXDL = LRXDL).

15.5.7.4 Data Length in Tx Response

Figure 15-10. LIN1.3 - Tx Response - No Error

●The user initializes LTXDL field before setting the Tx response command,

●After setting the Tx response command, LRXDL is reset by hardware,

●LTXDL will remain unchanged during Tx (during busy signal),

●LRXDL will count the number of transmitted bytes (during busy signal),

●If an error occurs, Tx stops, the corresponding error flag is set and LRXDL will give the number of transmitted bytes

without error,

●If no error occurs, LTXOK is set after the transmission of the CHECKSUM, LTXDL will be unchanged (and

LRXDL = LTXDL).

DATA-0

LCMD = Rx Response LCMD2..0 = 000b

LINDLR = 0x?4

(*): LRXDL and LTXDL updated by user

?01234

LIDOK

LIN bus

LRXDL (*)

LTXDL (*)

LBUSY

1st Byte 2nd Byte 3rd Byte 4th Byte

DATA-1 DATA-2 DATA-3 CHECKSUM

LRXOK

DATA-0

LCMD = Tx Response LCMD2..0 = 000b

(*): LRXDL and LTXDL updated by Rx Response or Tx Response task

401234

LIN bus

LRXDL (*)

LTXDL (*)

LBUSY

1st Byte 2nd Byte 3rd Byte 4th Byte

DATA-1 DATA-2 DATA-3 CHECKSUM

LIDOK LTXOK

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15.5.7.5 Data Length after Error

Figure 15-11. Tx Response - Error

Note: Information on response (ex: error on byte) is only available at the end of the serialization/de-serialization of

the byte.

15.5.7.6 Data Length in UART Mode

●The UART mode forces LRXDL and LTXDL to 0 and disables the writing in LINDLR register,

●Note that after reset, LRXDL and LTXDL are also forced to 0.

15.5.8 xxOK Flags

There are three xxOK flags in LINSIR register:

●LIDOK: LIN identifier OK

It is set at the end of the header, either by the Tx header function or by the Rx header. In LIN 1.3, before generating

LIDOK, the controller updates the LRXDL & LTXDL fields in LINDLR register.

It is not driven in UART mode.

●LRXOK: LIN RX response complete

It is set at the end of the response by the Rx response function in LIN mode and once a character is received in UART

mode.

●LTXOK: LIN TX response complete

It is set at the end of the response by the Tx response function in LIN mode and once a character has been sent in

UART mode.

These flags can generate interrupts if the corresponding enable interrupt bit is set in the LINENIR register (see Section

15.5.13 “Interrupts” on page 163).

DATA-0

LCMD = Tx Response

LCMD2..0 = 000b

40 1 2

LIN bus

LRXDL

LTXDL

LBUSY

1st Byte 2nd Byte 3rd Byte

LERR

DATA-1 DATA-2

ERROR

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15.5.9 xxERR Flags

LERR bit of the LINSIR register is an logical ‘OR’ of all the bits of LINERR register (see Section 15.5.13 “Interrupts” on page

163). There are eight flags:

●LBERR = LIN Bit ERRor.

A unit that is sending a bit on the bus also monitors the bus. A LIN bit error will be flagged when the bit value that is

monitored is different from the bit value that is sent. After detection of a LIN bit error the transmission is aborted.

●LCERR = LIN Checksum ERRor.

A LIN checksum error will be flagged if the inverted modulo-256 sum of all received data bytes (and the protected

identifier in LIN 2.1) added to the checksum does not result in 0xFF.

●LPERR = LIN Parity ERRor (identifier).

A LIN parity error in the IDENTIFIER field will be flagged if the value of the parity bits does not match with the identifier

value. (See LP[1:0] bits in Section 15.6.8 “LIN Identifier Register - LINIDR” on page 170). A LIN slave application does

not distinguish between corrupted parity bits and a corrupted identifier. The hardware does not undertake any

correction. However, the LIN slave application has to solve this as:

●known identifier (parity bits corrupted),

●or corrupted identifier to be ignored,

●or new identifier.

●LSERR = LIN Synchronization ERRor.

A LIN synchronization error will be flagged if a slave detects the edges of the SYNCH field outside the given

tolerance.

●LFERR = LIN framing ERRor.

A framing error will be flagged if dominant STOP bit is sampled.

Same function in UART mode.

●LTOERR = LIN time out ERRor.

A time-out error will be flagged if the MESSAGE frame is not fully completed within the maximum length TFrame_Maximum

by any slave task upon transmission of the SYNCH and IDENTIFIER fields (see Section 15.5.10 “Frame Time Out” on

page 162).

●LOVERR = LIN OVerrun ERRor.

Overrun error will be flagged if a new command (other than LIN Abort) is entered while ‘busy signal’ is present.

In UART mode, an overrun error will be flagged if a received byte overwrites the byte stored in the serial input buffer.

●LABORT

LIN abort transfer reflects a previous LIN Abort command (LCMD[2..0] = 000) while ‘busy signal’ is present.

After each LIN error, the LIN controller stops its previous activity and returns to its withdrawal mode (LCMD[2..0] = 000 b) as

illustrated in Figure 15-11 on page 161.

Writing 1 in LERR of LINSIR register resets LERR bit and all the bits of the LINERR register.

15.5.10 Frame Time Out

According to the LIN protocol, a frame time-out error is flagged if: T Frame > T Frame_Maximum.

This feature is implemented in the LIN/UART controller.

Figure 15-12.LIN timing and frame time-out

Field Field

SYNC

Header

Header_Nominal

Response_Nominal

Frame_Nominal

34 x T

Bit

10 (Number_of_Data + 1) x T

Bit

Header_ Nominal

+ T

Response_Nominal

Header_Maximum

Response_Maximum

Frame_Maximum

1.4 x T

Header_Nominal

1.4 x T

Response_Nominal

Header_ Maximum

+ T

Response_Maximum

Frame

Response

BREAK

Field

Nominal Maximum before Time-out

PROTECTED

IDENTIFIER

Field

DATA-0

Field

DATA-n CHECKSUM

Field

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15.5.11 Break-in-data

According to the LIN protocol, the LIN/UART controller can detect the BREAK/SYNC field sequence even if the break is

partially superimposed with a byte of the response. When a BREAK/SYNC field sequence happens, the transfer in progress

is aborted and the processing of the new frame starts.

●On slave node(s), an error is generated (i.e. LBERR in case of Tx response or LFERR in case of Rx response).

Information on data error is also available, refer to the Section 15.5.7.5 “Data Length after Error” on page 161.

●On master node, the user (code) is responsible for this aborting of frame. To do this, the master task has first to abort

the on-going communication (clearing LCMD bits - LIN abort command) and then to apply the Tx header command. In

this case, the abort error flag - LABORT - is set.

On the slave node, the BREAK detection is processed with the synchronization setting available when the LIN/UART

controller processed the (aborted) response. But the re-synchronization restarts as usual. Due to a possible difference of

timing reference between the BREAK field and the rest of the frame, the time-out values can be slightly inaccurate.

15.5.12 Checksum

The last field of a frame is the checksum.

In LIN 2.1, the checksum contains the inverted eight bit sum with carry over all data bytes and the protected identifier. This

calculation is called enhanced checksum

In LIN 1.3, the checksum contains the inverted eight bit sum with carry over all data bytes. This calculation is called classic

checksum.

Frame identifiers 60 (0x3C) to 61 (0x3D) shall always use classic checksum.

15.5.13 Interrupts

As shown in Figure 15-13 on page 163, the four communication flags of the LINSIR register are combined to drive two

interrupts. Each of these flags have their respective enable interrupt bit in LINENIR register.

(see Section 15.5.8 “xxOK Flags” on page 161 and Section 15.5.9 “xxERR Flags” on page 162).

Figure 15-13.LIN Interrupt Mapping

CHECKSUM 255 unsigned char DATA n









PROTECTED ID.+







unsigned char DATA n









PROTECTED ID.+







8»







 

 

 

–=

CHECKSUM 255 unsigned char DATAn









unsigned char DATAn









8»













–=

LABORT

LTOERR

LOVERR

LFERR

LSERR

LPERR

LCERR

LBERR

LERR LIN ERR

LIN TC

LIDOK

LTXOK

LRXOK

LENERR

LINENIR.3 LINENIR.2 LINENIR.1 LINENIR.0

LENIDOK LENTXOK LENRXOK

LINSIR.3

LINSIR.2

LINERR.7

LINERR.6

LINERR.5

LINERR.4

LINERR.3

LINERR.2

LINERR.1

LINERR.0 LINSIR.1

LINSIR.0

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15.5.14 Message Filtering

Message filtering based upon the whole identifier is not implemented. Only a status for frame headers having 0x3C, 0x3D,

0x3E and 0x3F as identifier is available in the LINSIR register.

The LIN protocol says that a message with an identifier from 60 (0x3C) up to 63 (0x3F) uses a classic checksum (sum over

the data bytes only). Software will be responsible for switching correctly the LIN13 bit to provide/check this expected

checksum (the insertion of the ID field in the computation of the CRC is set - or not - just after entering the Rx or Tx response

command).

15.5.15 Data Management

15.5.15.1 LIN FIFO Data Buffer

To preserve register allocation, the LIN data buffer is seen as a FIFO (with address pointer accessible). This FIFO is

accessed via the LINDX[2..0] field of LINSEL register through the LINDAT register.

LINDX[2..0], the data index, is the address pointer to the required data byte. The data byte can be read or written. The data

index is automatically incremented after each LINDAT access if the LAINC (active low) bit is cleared. A roll-over is

implemented, after data index=7 it is data index=0. Otherwise, if LAINC bit is set, the data index needs to be written

(updated) before each LINDAT access.

The first byte of a LIN frame is stored at the data index=0, the second one at the data index=1, and so on. Nevertheless,

LINSEL must be initialized by the user before use.

15.5.15.2 UART Data Register

The LINDAT register is the data register (no buffering - no FIFO). In write access, LINDAT will be for data out and in read

access, LINDAT will be for data in.

In UART mode the LINSEL register is unused.

15.5.16 OCD Support

When a debugger break occurs, the state machine of the LIN/UART controller is stopped (included frame time-out) and

further communication may be corrupted.

Table 15-4. Frame Status

LIDST[2..0] Frame Status

0xx bNo specific identifier

100 b60 (0x3C) identifier

101 b61 (0x3D) identifier

110 b62 (0x3E) identifier

111 b63 (0x3F) identifier

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15.6 LIN / UART Register Description

Table 15-5. LIN/UART Register Bits Summary

Name Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0

LINCR LSWRES LIN13 LCONF1 LCONF0 LENA LCMD2 LCMD1 LCMD0

0 R/W 0 R/W 0 R/W 0 R/W 0 R/W 0 R/W 0 R/W 0 R/W

LINSIR LIDST2 LIDST1 LIDST0 LBUSY LERR LIDOK LTXOK LRXOK

0 R 0 R 0 R 0 R 0 R/Wone 0R/Wone 0R/Wone 0R/Wone

LINENIR ————LENERR LENIDOK LENTXOK LENRXOK

0 R 0 R 0 R 0 R 0 R/W 0 R/W 0 R/W 0 R/W

LINERR LABORT LTOERR LOVERR LFERR LSERR LPERR LCERR LBERR

0 R 0 R 0 R 0 R 0 R 0 R 0 R 0 R

LINBTR LDISR LBT5 LBT4 LBT3 LBT2 LBT1 LBT0

0 R/W 0 R 1 R/(W) 0R/(W) 0R/(W) 0R/(W) 0R/(W) 0R/(W)

LINBRRL LDIV7 LDIV6 LDIV5 LDIV4 LDIV3 LDIV2 LDIV1 LDIV0

0 R/W 0 R/W 0 R/W 0 R/W 0 R/W 0 R/W 0 R/W 0 R/W

LINBRRH ————LDIV11 LDIV10 LDIV9 LDIV8

0 R 0 R 0 R 0 R 0 R/W 0 R/W 0 R/W 0 R/W

LINDLR LTXDL3 LTXDL2 LTXDL1 LTXDL0 LRXDL3 LRXDL2 LRXDL1 LRXDL0

0 R/W 0 R/W 0 R/W 0 R/W 0 R/W 0 R/W 0 R/W 0 R/W

LINIDR LP1 LP0 LID5/LDL1 LID4/LDL0 LID3 LID2 LID1 LID0

1 R 0 R 0 R/W 0 R/W 0 R/W 0 R/W 0 R/W 0 R/W

LINSEL ————LAINC LINDX2 LINDX1 LINDX0

0 R 0 R 0 R 0 R 0 R/W 0 R/W 0 R/W 0 R/W

LINDAT LDATA7 LDATA6 LDATA5 LDATA4 LDATA3 LDATA2 LDATA1 LDATA0

0 R/W 0 R/W 0 R/W 0 R/W 0 R/W 0 R/W 0 R/W 0 R/W

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15.6.1 LIN Control Register - LINCR

• Bit 7 - LSWRES: Software Reset

●0 = No action,

●1 = Software reset (this bit is self-reset at the end of the reset procedure).

• Bit 6 - LIN13: LIN 1.3 mode

●0 = LIN 2.1 (default),

●1 = LIN 1.3.

• Bit 5:4 - LCONF[1:0]: Configuration

a. LIN mode (default = 00):

●00 = LIN standard configuration (listen mode “off”, CRC “on” and frame_time_out “on”,

●01 = no CRC, no frame_time_out (listen mode “off”),

●10 = no frame_time_out (listen mode “off” and CRC “on”),

●11 = listening mode (CRC “on” and frame_time_out “on”).

b. UART mode (default = 00):

●00 = 8-bit, no parity (listen mode “off”),

●01 = 8-bit, even parity (listen mode “off”),

●10 = 8-bit, odd parity (listen mode “off”),

●11 = listening mode, 8-bit, no parity.

• Bit 3 - LENA: Enable

●0 = disable (both LIN and UART modes),

●1 = enable (both LIN and UART modes).

• Bit 2:0 - LCMD[2..0]: Command and mode

The command is only available if LENA is set.

●000 = LIN Rx header - LIN abort,

●001 = LIN Tx header,

●010 = LIN Rx response,

●011 = LIN Tx response,

●100 = UART Rx and Tx byte disable,

●11x = UART Rx byte enable,

●1x1 = UART Tx byte enable.

Bit 7 6543210

LSWRES LIN13 LCONF1 LCONF0 LENA LCMD2 LCMD1 LCMD0 LINCR

Read/Write R/W R/W R/W R/W R/W R/W R/W R/W

Initial Value0 0000000

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15.6.2 LIN Status and Interrupt Register - LINSIR

• Bits 7:5 - LIDST[2:0]: Identifier Status

●0xx = no specific identifier,

●100 = identifier 60 (0x3C),

●101 = identifier 61 (0x3D),

●110 = identifier 62 (0x3E),

●111 = identifier 63 (0x3F).

• Bit 4 - LBUSY: Busy Signal

●0 = not busy,

●1 = busy (receiving or transmitting).

• Bit 3 - LERR: Error Interrupt

It is a logical OR of LINERR register bits. This bit generates an interrupt if its respective enable bit - LENERR - is set in

LINENIR.

●0 = no error,

●1 = an error has occurred.

The user clears this bit by writing 1 in order to reset this interrupt. Resetting LERR also resets all LINERR bits. In UART

mode, this bit is also cleared by reading LINDAT.

• Bit 2 - LIDOK: Identifier Interrupt

This bit generates an interrupt if its respective enable bit - LENIDOK - is set in LINENIR.

●0 = no identifier,

●1 = slave task: Identifier present, master task: Tx header complete.

The user clears this bit by writing 1, in order to reset this interrupt.

• Bit 1 - LTXOK: Transmit Performed Interrupt

This bit generates an interrupt if its respective enable bit - LENTXOK - is set in LINENIR.

●0 = no Tx,

●1 = Tx response complete.

The user clears this bit by writing 1, in order to reset this interrupt.

In UART mode, this bit is also cleared by writing LINDAT.

• Bit 0 - LRXOK: Receive Performed Interrupt

This bit generates an interrupt if its respective enable bit - LENRXOK - is set in LINENIR.

●0 = no Rx

●1 = Rx response complete.

The user clears this bit by writing 1, in order to reset this interrupt.

In UART mode, this bit is also cleared by reading LINDAT.

Bit 76543210

LIDST2 LIDST1 LIDST0 LBUSY LERR LIDOK LTXOK LRXOK LINSIR

Read/Write RRRRR/WoneR/WoneR/WoneR/Wone

Initial Value00000000

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15.6.3 LIN Enable Interrupt Register - LINENIR

• Bits 7:4 - Reserved Bits

These bits are reserved for future use. For compatibility with future devices, they must be written to zero when LINENIR is

written.

• Bit 3 - LENERR: Enable Error Interrupt

●0 = Error interrupt masked,

●1 = Error interrupt enabled.

• Bit 2 - LENIDOK: Enable Identifier Interrupt

●0 = Identifier interrupt masked,

●1 = Identifier interrupt enabled.

• Bit 1 - LENTXOK: Enable Transmit Performed Interrupt

●0 = Transmit performed interrupt masked,

●1 = Transmit performed interrupt enabled.

• Bit 0 - LENRXOK: Enable Receive Performed Interrupt

●0 = Receive performed interrupt masked,

●1 = Receive performed interrupt enabled.

15.6.4 LIN Error Register - LINERR

• Bit 7 - LABORT: Abort Flag

●0 = No warning,

●1 = LIN abort command occurred.

This bit is cleared when LERR bit in LINSIR is cleared.

• Bit 6 - LTOERR: Frame_Time_Out Error Flag

●0 = No error,

●1 = Frame_time_out error.

This bit is cleared when LERR bit in LINSIR is cleared.

• Bit 5 - LOVERR: Overrun Error Flag

●0 = No error,

●1 = Overrun error.

This bit is cleared when LERR bit in LINSIR is cleared.

Bit 7654 3 2 1 0

- - - - LENERR LENIDOK LENTXOK LENRXOK LINENIR

Read/Write R R R R R/W R/W R/W R/W

Initial Value 0 0 0 0 0 0 0 0

Bit 76543210

LABORT LTOERR LOVERR LFERR LSERR LPERR LCERR LBERR LINERR

Read/Write RRRRRRRR

Initial Value00000000

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• Bit 4 - LFERR: Framing Error Flag

●0 = No error,

●1 = Framing error.

This bit is cleared when LERR bit in LINSIR is cleared.

• Bit 3 - LSERR: Synchronization Error Flag

●0 = No error,

●1 = Synchronization error.

This bit is cleared when LERR bit in LINSIR is cleared.

• Bit 2 - LPERR: Parity Error Flag

●0 = No error,

●1 = Parity error.

This bit is cleared when LERR bit in LINSIR is cleared.

• Bit 1 - LCERR: Checksum Error Flag

●0 = No error,

●1 = Checksum error.

This bit is cleared when LERR bit in LINSIR is cleared.

• Bit 0 - LBERR: Bit Error Flag

●0 = no error,

●1 = Bit error.

This bit is cleared when LERR bit in LINSIR is cleared.

15.6.5 LIN Bit Timing Register - LINBTR

• Bit 7 - LDISR: Disable Bit Timing Re synchronization

●0 = Bit timing re-synchronization enabled (default),

●1 = Bit timing re-synchronization disabled.

• Bits 5:0 - LBT[5:0]: LIN Bit Timing

Gives the number of samples of a bit.

Sample-time = (1 / fclki/o) x (LDIV[11..0] + 1)

Default value: LBT[6:0]=32 — Min. value: LBT[6:0]=8 — Max. value: LBT[6:0]=63

Bit 7654321 0

LDISR - LBT5 LBT4 LBT3 LBT2 LBT1 LBT0 LINBTR

Read/Write R/W R R/(W) R/(W) R/(W) R/(W) R/(W) R/(W)

Initial Value0010000 0

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15.6.6 LIN Baud Rate Register - LINBRR

• Bits 15:12 - Reserved Bits

These bits are reserved for future use. For compatibility with future devices, they must be written to zero when LINBRR is

written.

• Bits 11:0 - LDIV[11:0]: Scaling of clki/o Frequency

The LDIV value is used to scale the entering clki/o frequency to achieve appropriate LIN or UART baud rate.

15.6.7 LIN Data Length Register - LINDLR

• Bits 7:4 - LTXDL[3:0]: LIN Transmit Data Length

In LIN mode, this field gives the number of bytes to be transmitted (clamped to 8 Max).

In UART mode this field is unused.

• Bits 3:0 - LRXDL[3:0]: LIN Receive Data Length

In LIN mode, this field gives the number of bytes to be received (clamped to 8 Max).

In UART mode this field is unused.

15.6.8 LIN Identifier Register - LINIDR

• Bits 7:6 - LP[1:0]: Parity

In LIN mode:

LP0 = LID4 ^ LID2 ^ LID1 ^ LID0

LP1 = ! ( LID1 ^ LID3 ^ LID4 ^ LID5 )

In UART mode this field is unused.

Bit 76543210

LDIV7 LDIV6 LDIV5 LDIV4 LDIV3 LDIV2 LDIV1 LDIV0 LINBRRL

----LDIV11LDIV10LDIV9LDIV8LINBRRH

Bit 151413121110 9 8

Read/Write R/W R/W R/W R/W R/W R/W R/W R/W

Initial Value00000000

Bit 76543210

LTXDL3 LTXDL2 LTXDL1 LTXDL0 LRXDL3 LRXDL2 LRXDL1 LRXDL0 LINDLR

Read/Write R/W R/W R/W R/W R/W R/W R/W R/W

Initial Value00000000

Bit 76 5 4 3210

LP1 LP0 LID5 /

LDL1

LID4 /

LDL0 LID3 LID2 LID1 LID0 LINIDR

Read/Write R R R/W R/W R/W R/W R/W R/W

Initial Value00 0 0 0000

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• Bits 5:4 - LDL[1:0]: LIN 1.3 Data Length

In LIN 1.3 mode:

●00 = 2-byte response,

●01 = 2-byte response,

●10 = 4-byte response,

●11 = 8-byte response.

In UART mode this field is unused.

• Bits 3:0 - LID[3:0]: LIN 1.3 Identifier

In LIN 1.3 mode: 4-bit identifier.

In UART mode this field is unused.

• Bits 5:0 - LID[5:0]: LIN 2.1 Identifier

In LIN 2.1 mode: 6-bit identifier (no length transported).

In UART mode this field is unused.

15.6.9 LIN Data Buffer Selection Register - LINSEL

• Bits 7:4 - Reserved Bits

These bits are reserved for future use. For compatibility with future devices, they must be written to zero when LINSEL is

written.

• Bit 3 - LAINC: Auto Increment of Data Buffer Index

In LIN mode:

●0 = Auto incrementation of FIFO data buffer index (default),

●1 = No auto incrementation.

In UART mode this field is unused.

• Bits 2:0 - LINDX 2:0: FIFO LIN Data Buffer Index

In LIN mode: location (index) of the LIN response data byte into the FIFO data buffer. The FIFO data buffer is accessed

through LINDAT.

In UART mode this field is unused.

Bit 76543210

----LAINCLINDX2LINDX1LINDX0LINSEL

Read/Write----R/WR/WR/WR/W

Initial Value----0000

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15.6.10 LIN Data Register - LINDAT

• Bits 7:0 - LDATA[7:0]: LIN Data In / Data out

In LIN mode: FIFO data buffer port.

In UART mode: data register (no data buffer - no FIFO).

●In write access, data out.

●In read access, data in.

Bit 76543210

LDATA7 LDATA6 LDATA5 LDATA4 LDATA3 LDATA2 LDATA1 LDATA0 LINDAT

Read/Write R/W R/W R/W R/W R/W R/W R/W R/W

Initial Value00000000

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16. ISRC - Current Source

16.1 Features

●100µA Constant current source

●±10% Absolute Accuracy

The Atmel® ATtiny87/167 features a 100µA ±10% Current Source. Up on request, the current is flowing through an external

resistor. The voltage can be measured on the dedicated pin shared with the ADC. Using a resistor in series with a ≤ 0.5%

tolerance is recommended. To protect the device against big values, the ADC must be configured with AVcc as internal

reference to perform the first measurement. Afterwards, another internal reference can be chosen according to the previous

measured value to refine the result.

When ISRCEN bit is set, the ISRC pin sources 100µA. Otherwise this pin keeps its initial function.

Figure 16-1. Current Source Block Diagram

16.2 Typical applications

16.2.1 LIN Current Source

During the configuration of a LIN node in a cluster, it may be necessary to attribute dynamically an unique physical address

to every cluster node. The way to do it is not described in the LIN protocol.

The current source offers an excellent solution to associate a physical address to the application supported by the LIN node.

A full dynamic node configuration can be used to set-up the LIN nodes in a cluster.

Atmel ATtiny87/167 proposes to have an external resistor used in conjunction with the current source. The device measures

the voltage to the boundaries of the resistance via the analog to digital converter. The resulting voltage defines the physical

address that the communication handler will use when the node will participate in LIN communication.

ADC Input

AVCC

ISRCEN

100μA

ADCn/ ISRC

External

Resistor

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In automotive applications, distributed voltages are very disturbed. The internal current source solution of Atmel

ATtiny87/167 immunizes the address detection the against any kind of voltage variations.

Table 16-1. Example of Resistor Values (±5%) for a 8-address System (AVcc = 5V(1))

Physical

Address

Resistor Value

Rload (Ohm)

Typical Measured

Voltage (V)

Minimum

Reading with a

2.56V ref

Typical Reading

with a 2.56V ref

Maximum

Reading with a

2.56V ref

01 000 0.1 40

12 200 0.22 88

23 300 0.33 132

34 700 0.47 188

46 800 0.68 272

510 000 1400

615 000 1.5 600

722 000 2.2 880

Table 16-2. Example of Resistor Values (±1%) for a 16-address System (AVcc = 5V(1))

Physical

Address

Resistor Value

Rload (Ohm)

Typical Measured

Voltage (V)

Minimum

Reading with a

2.56V ref

Typical Reading

with a 2.56V ref

Miximum

Reading with a

2.56V ref

01 000 0.1 38 40 45

11 200 0.12 46 48 54

21500 0.15 57 60 68

31800 0.18 69 72 81

42200 0.22 84 88 99

52700 0.27 104 108 122

63300 0.33 127 132 149

74700 0.47 181 188 212

86 800 0.68 262 272 306

98 200 0.82 316 328 369

10 10 000 1.0 386 400 450

11 12 000 1.2 463 480 540

12 15 000 1.5 579 600 675

13 18 000 1.8 694 720 810

14 22 000 2.2 849 880 989

15 27 000 2.7 1023 1023 1023

Note: 1. 5V range: Max Rload 30K

3V range: Max Rload 15K

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16.2.2 Current Source for Low Cost Transducer

An external transducer based on a variable resistor can be connected to the current source.

This can be, for instance:

●A thermistor, or temperature-sensitive resistor, used as a temperature sensor,

●A CdS photoconductive cell, or luminosity-sensitive resistor, used as a luminosity sensor,

●...

Using the current source with this type of transducer eliminates the need for additional parts otherwise required in resistor

network or wheatstone bridge.

16.2.3 Voltage Reference for External Devices

An external resistor used in conjunction with the current source can be used as voltage reference for external devices. Using

a resistor in serie with a lower tolerance than the current source accuracy (≤2%) is recommended. Table 16-2 on page 174

gives an example of voltage references using standard values of resistors.

16.2.4 Threshold Reference for Internal Analog Comparator

An external resistor used in conjunction with the current source can be used as threshold reference for internal analog

Comparator (see Section 18. “AnaComp - Analog Comparator” on page 194). This can be connected to AIN0 (negative

analog compare input pin) as well as AIN1 (positive analog compare input pin). Using a resistor in serie with a lower

tolerance than the current source accuracy (≤2%) is recommended. Table 16-2 on page 174 gives an example of threshold

references using standard values of resistors.

16.3 Control Register

16.3.1 AMISCR – Analog Miscellaneous Control Register

• Bit 0 – ISRCEN: Current Source Enable

Writing this bit to one enables the current source as shown in Figure 16-1 on page 173. It is recommended to use DIDR

register bit function when ISRCEN is set. It also recommended to turn off the current source as soon as possible (ex: once

the ADC measurement is done).

Bit 76543210

-----AREFEN XREFEN ISRCEN AMISCR

Read/Write RRRRRR/WR/WR/W

Initial Value00000000

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17. ADC – Analog to Digital Converter

17.1 Features

●10-bit resolution

●1.0 LSB integral non-linearity

●±2 LSB absolute accuracy

●13 - 260µs conversion time (low - high resolution)

●Up to 15kSPS at maximum resolution

●11 multiplexed single ended input channels

●8 differential input pairs with selectable gain

●Temperature sensor input channel

●Voltage from internal current source driving (ISRC)

●Optional left adjustment for ADC result readout

●0 - AVcc ADC input voltage range

●Selectable 1.1V/2.56V ADC voltage reference

●Free running or single conversion mode

●ADC start conversion by auto triggering on interrupt sources

●Interrupt on ADC conversion complete

●Sleep mode noise canceler

●Unipolar/bipolar input mode

●Input polarity reversal mode

17.2 Overview

The Atmel® ATtiny87/167 features a 10-bit successive approximation ADC. The ADC is connected to a 11-channel analog

multiplexer which allows 16 differential voltage input combinations and 11 single-ended voltage inputs constructed from the

pins PA7..PA0 or PB7..PB4. The differential input is equipped with a programmable gain stage, providing amplification steps

of 8x or 20x on the differential input voltage before the A/D conversion. The single-ended voltage inputs refer to 0V (AGND).

The ADC contains a sample and hold circuit which ensures that the input voltage to the ADC is held at a constant level

during conversion. A block diagram of the ADC is shown in Figure 17-1 on page 177.

Internal reference voltages of nominally 1.1V or 2.56V are provided On-chip. Alternatively, AVcc can be used as reference

voltage for single ended channels. There are also options to output the internal 1.1V or 2.56V reference voltages or to input

an external voltage reference and turn-off the internal voltage reference. These options are selected using the REFS[1:0]

bits of the ADMUX control register and using AREFEN and XREFEN bits of the AMISCR control register.

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Figure 17-1. Analog to Digital Converter Block Schematic

Trigger

Select

Prescaler

Interrupt

Flags

ADC Conversion

Complete IRQ

Start

AVCC

ADC10

AGND

Bandgap

Reference

Temperature

Sensor

AVCC

Internal

2.56/ 1.1V

Reference

Mux.

Decoder

Sample and Hold

Comparator

ADC Multiplexer

Output

ADC Multiplexer

Select (ADMUX)

Analog Misc.

(AMISCR)

ADC Control and Status

Conversion Logic

ADC Data Register

(ADCH/ ADCL)

MUX[4..0]

XREFEN

AREFEN

REFS1

REFS0

ADLAR

10-bit DAC

Mux.

x8/ x20 Gain

Amplifier

Pos.

Input

Mux.

Neg.

Input

Mux.

ADSP[2..0]

ADTS[2..0]

ADC[9..0]

BIN

ADEN ADIE

ADIF

ADATE

ADSC

ADC9

ADC8

ADC7

ADC6

AREF

XREF

ADC5

ADC4

ISRC/ ADC3

ADC2

ADC1

ADC0

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17.3 Operation

The ADC converts an analog input voltage to a 10-bit digital value through successive approximation. The minimum value

represents AGND and the maximum value represents the voltage on AVcc, the voltage reference on AREF pin or an internal

1.1V/2.56V voltage reference.

The voltage reference for the ADC may be selected by writing to the REFS[1..0] bits in ADMUX and AREFEN bit in AMISCR.

The AVcc supply, the AREF pin or an internal 1.1V / 2.56V voltage reference may be selected as the ADC voltage reference.

The analog input channel and differential gain are selected by writing to the MUX[4..0] bits in ADMUX register. Any of the 11

ADC input pins ADC[10..0] can be selected as single ended inputs to the ADC. The positive and negative inputs to the

differential gain amplifier are described in Table 17-5 on page 189.

If differential channels are selected, the differential gain stage amplifies the voltage difference between the selected input

pair by the selected gain factor 8x or 20x, according to the setting of the MUX[4..0] bits in ADMUX register. This amplified

value then becomes the analog input to the ADC. If single ended channels are used, the gain amplifier is bypassed

altogether.

The on-chip temperature sensor is selected by writing the code defined in Table 17-5 on page 189 to the MUX[4..0] bits in

ADMUX register when its dedicated ADC channel is used as an ADC input.

A specific ADC channel (defined in Table 17-5 on page 189) is used to measure the voltage to the boundaries of an external

resistance flowing by a current driving by the Internal current source (ISRC).

The ADC is enabled by setting the ADC enable bit, ADEN in ADCSRA register. Voltage reference and input channel

selections will not go into effect until ADEN is set. The ADC does not consume power when ADEN is cleared, so it is

recommended to switch off the ADC before entering power saving sleep modes.

The ADC generates a 10-bit result which is presented in the ADC data registers, ADCH and ADCL. By default, the result is

presented right adjusted, but can optionally be presented left adjusted by setting the ADLAR bit in ADMUX register.

If the result is left adjusted and no more than 8-bit precision is required, it is sufficient to read ADCH. Otherwise, ADCL must

be read first, then ADCH, to ensure that the content of the data registers belongs to the same conversion. Once ADCL is

read, ADC access to data registers is blocked. This means that if ADCL has been read, and a conversion completes before

ADCH is read, neither register is updated and the result from the conversion is lost. When ADCH is read, ADC access to the

ADCH and ADCL registers is re-enabled.

The ADC has its own interrupt which can be triggered when a conversion completes. When ADC access to the data registers

is prohibited between reading of ADCH and ADCL, the interrupt will trigger even if the result is lost.

17.4 Starting a Conversion

A single conversion is started by writing a logical one to the ADC start conversion bit, ADSC. This bit stays high as long as

the conversion is in progress and will be cleared by hardware when the conversion is completed. If a different data channel

is selected while a conversion is in progress, the ADC will finish the current conversion before performing the channel

change.

Alternatively, a conversion can be triggered automatically by various sources. Auto triggering is enabled by setting the ADC

auto trigger Enable bit, ADATE in ADCSRA register. The trigger source is selected by setting the ADC trigger select bits,

ADTS in ADCSRB register (see description of the ADTS bits for a list of the trigger sources). When a positive edge occurs on

the selected trigger signal, the ADC prescaler is reset and a conversion is started. This provides a method of starting

conversions at fixed intervals. If the trigger signal still is set when the conversion completes, a new conversion will not be

started. If another positive edge occurs on the trigger signal during conversion, the edge will be ignored. Note that an

interrupt flag will be set even if the specific interrupt is disabled or the global interrupt enable bit in SREG register is cleared.

A conversion can thus be triggered without causing an interrupt. However, the interrupt flag must be cleared in order to

trigger a new conversion at the next interrupt event.

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Figure 17-2. ADC Auto Trigger Logic

Using the ADC interrupt flag as a trigger source makes the ADC start a new conversion as soon as the ongoing conversion

has finished. The ADC then operates in free running mode, constantly sampling and updating the ADC data register. The

first conversion must be started by writing a logical one to the ADSC bit in ADCSRA register. In this mode the ADC will

perform successive conversions independently of whether the ADC interrupt flag, ADIF is cleared or not.

If Auto triggering is enabled, single conversions can be started by writing ADSC in ADCSRA register to one. ADSC can also

be used to determine if a conversion is in progress. The ADSC bit will be read as one during a conversion, independently of

how the conversion was started.

17.5 Prescaling and Conversion Timing

Figure 17-3. ADC Prescaler

By default, the successive approximation circuitry requires an input clock frequency between 50kHz and 200kHz to get

maximum resolution. If a lower resolution than 10 bits is needed, the input clock frequency to the ADC can be higher than

200kHz to get a higher sample rate.

The ADC module contains a prescaler, which generates an acceptable ADC clock frequency from any CPU frequency above

100kHz. The prescaling is set by the ADPS bits in ADCSRA register. The prescaler starts counting from the moment the

ADC is switched on by setting the ADEN bit in ADCSRA register. The prescaler keeps running for as long as the ADEN bit is

set, and is continuously reset when ADEN is low.

When initiating a single ended conversion by setting the ADSC bit in ADCSRA register, the conversion starts at the following

rising edge of the ADC clock cycle.

A normal conversion takes 13 ADC clock cycles. The first conversion after the ADC is switched on (ADEN in ADCSRA

Edge

Detector

Conversion

Logic

ADC Prescaler

ADIF

ADSC

ADATE

START

CLK

ADC

CLK

ADTS[2:0]

SOURCE 1

SOURCE n

7-Bit ADC Prescaler

ADEN

START

CLK

ADPS0

ADPS1

ADPS2

Reset

CK/2

CK/4

CK/8

CK/16

CK/32

CK/64

CK/128

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The actual sample-and-hold takes place 1.5 ADC clock cycles after the start of a normal conversion and 14.5 ADC clock

cycles after the start of an first conversion. When a conversion is complete, the result is written to the ADC data registers,

and ADIF is set. In single conversion mode, ADSC is cleared simultaneously. The software may then set ADSC again, and a

new conversion will be initiated on the first rising ADC clock edge.

When auto triggering is used, the prescaler is reset when the trigger event occurs. This assures a fixed delay from the trigger

event to the start of conversion. In this mode, the sample-and-hold takes place 2 ADC clock cycles after the rising edge on

the trigger source signal. Three additional CPU clock cycles are used for synchronization logic.

In free running mode, a new conversion will be started immediately after the conversion completes, while ADSC remains

high. For a summary of conversion times, see Table 17-1 on page 181.

Figure 17-4. ADC Timing Diagram, First Conversion (Single Conversion Mode)

Figure 17-5. ADC Timing Diagram, Single Conversion

1 2 12 13 14 15 16 17 18 19 20 21 22 23 24 25 1 2 3

Cycle Number

First Conversion

Sign and MSB of Result

LSB of Result

Conversion

MUX and REFS

Update

Conversion

Complete MUX and REFS

Update

ADC Clock

ADEN

ADSC

ADIF

ADCH

ADCL

Sample and Hold

12345678910111213 123

Cycle Number

One Conversion Next Conversion

MUX and REFS

Update

Conversion

Complete MUX and REFS

Update

ADC Clock

ADSC

ADIF

ADCH

ADCL

Sample and Hold

Sign and MSB of Result

LSB of Result

/////////////

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Figure 17-6. ADC Timing Diagram, Auto Triggered Conversion

Figure 17-7. ADC Timing Diagram, Free Running Conversion

Table 17-1. ADC Conversion Time

Condition

Sample and Hold

(Cycles from Start of Conversion) Conversion Time (Cycles)

First conversion 13.5 cycles 25 cycles

Normal conversions 1.5 cycles 13 cycles

Auto Triggered conversions 2 cycles 13.5 cycles

1 2 3 4 5 6 7 8 9 10 11 12 13 1 2

Cycle Number

One Conversion Next Conversion

MUX and REFS

Update

Prescaler

Reset

Prescale

Reset

Conversion

Complete

ADC Clock

Trigger

Source

ADIF

ADATE

ADCH

ADCL

Sample and Hold

Sign and MSB of Result

LSB of Result

11 12 13 1 2 3 4

Cycle Number

One Conversion Next Conversion

MUX and REFS

Update

Conversion

Complete

ADC Clock

ADSC

ADIF

ADCH

ADCL

Sample and Hold

Sign and MSB of Result

LSB of Result

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17.6 Changing Channel or Reference Selection

The MUX[4:0] and REFS[1:0] bits in the ADMUX register are single buffered through a temporary register to which the CPU

has random access. This ensures that the channels and reference selection only takes place at a safe point during the

conversion. The channel and reference selection is continuously updated until a conversion is started. Once the conversion

starts, the channel and reference selection is locked to ensure a sufficient sampling time for the ADC. Continuous updating

resumes in the last ADC clock cycle before the conversion completes (ADIF in ADCSRA register is set). Note that the

conversion starts on the following rising ADC clock edge after ADSC is written. The user is thus advised not to write new

channel or reference selection values to ADMUX until one ADC clock cycle after ADSC is written.

If auto triggering is used, the exact time of the triggering event can be indeterministic. Special care must be taken when

updating the ADMUX register, in order to control which conversion will be affected by the new settings.

If both ADATE and ADEN is written to one, an interrupt event can occur at any time. If the ADMUX register is changed in this

period, the user cannot tell if the next conversion is based on the old or the new settings. ADMUX can be safely updated in

the following ways:

a. When ADATE or ADEN is cleared.

b. During conversion, minimum one ADC clock cycle after the trigger event.

c. After a conversion, before the interrupt flag used as trigger source is cleared.

When updating ADMUX in one of these conditions, the new settings will affect the next ADC conversion.

17.6.1 ADC Input Channels

When changing channel selections, the user should observe the following guidelines to ensure that the correct channel is

selected:

In single conversion mode, always select the channel before starting the conversion. The channel selection may be changed

one ADC clock cycle after writing one to ADSC. However, the simplest method is to wait for the conversion to complete

before changing the channel selection.

In Free Running mode, always select the channel before starting the first conversion. The channel selection may be

changed one ADC clock cycle after writing one to ADSC. However, the simplest method is to wait for the first conversion to

complete, and then change the channel selection. Since the next conversion has already started automatically, the next

result will reflect the previous channel selection. Subsequent conversions will reflect the new channel selection.

17.6.2 ADC Voltage Reference

The voltage reference for the ADC (VREF) indicates the conversion range for the ADC. Single ended channels that exceed

VREF will result in codes close to 0x3FF. VREF can be selected as either AVcc, internal 1.1V/2.56V voltage reference or

external AREF pin. The first ADC conversion result after switching voltage reference source may be inaccurate, and the user

is advised to discard this result.

17.7 ADC Noise Canceler

The ADC features a noise canceler that enables conversion during sleep mode to reduce noise induced from the CPU core

and other I/O peripherals. The noise canceler can be used with ADC noise reduction and idle mode. To make use of this

feature, the following procedure should be used:

a. Make sure that the ADC is enabled and is not busy converting. Single conversion mode must be selected and the

ADC conversion complete interrupt must be enabled.

b. Enter ADC noise reduction mode (or idle mode). The ADC will start a conversion once the CPU has been halted.

c. If no other interrupts occur before the ADC conversion completes, the ADC interrupt will wake up the CPU and

execute the ADC conversion complete interrupt routine. If another interrupt wakes up the CPU before the ADC

conversion is complete, that interrupt will be executed, and an ADC conversion complete interrupt request will be

generated when the ADC conversion completes. The CPU will remain in active mode until a new sleep command

is executed.

Note that the ADC will not be automatically turned off when entering other sleep modes than Idle mode and ADC noise

reduction mode. The user is advised to write zero to ADEN before entering such sleep modes to avoid excessive power

consumption.

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17.7.1 Analog Input Circuitry

The analog input circuitry for single ended channels is illustrated in Figure 17-8. An analog source applied to ADCn is

subjected to the pin capacitance and input leakage of that pin, regardless of whether that channel is selected as input for the

ADC. When the channel is selected, the source must drive the S/H capacitor through the series resistance (combined

resistance in the input path).

The ADC is optimized for analog signals with an output impedance of approximately 10k or less. If such a source is used,

the sampling time will be negligible. If a source with higher impedance is used, the sampling time will depend on how long

time the source needs to charge the S/H capacitor, with can vary widely. The user is recommended to only use low impedant

sources with slowly varying signals, since this minimizes the required charge transfer to the S/H capacitor.

Signal components higher than the nyquist frequency (fADC/2) should not be present to avoid distortion from unpredictable

signal convolution. The user is advised to remove high frequency components with a low-pass filter before applying the

signals as inputs to the ADC.

Figure 17-8. Analog Input Circuitry

17.7.2 Analog Noise Canceling Techniques

Digital circuitry inside and outside the device generates EMI which might affect the accuracy of analog measurements. If

conversion accuracy is critical, the noise level can be reduced by applying the following techniques:

a. Keep analog signal paths as short as possible. Make sure analog tracks run over the analog ground plane, and

keep them well away from high-speed switching digital tracks.

b. Use the ADC noise canceler function to reduce induced noise from the CPU.

c. If any port pins are used as digital outputs, it is essential that these do not switch while a conversion is in progress.

17.7.3 ADC Accuracy Definitions

An n-bit single-ended ADC converts a voltage linearly between GND and VREF in 2n steps (LSBs). The lowest code is read

as 0, and the highest code is read as 2n-1.

Several parameters describe the deviation from the ideal behavior:

●Offset: The deviation of the first transition (0x000 to 0x001) compared to the ideal transition (at 0.5 LSB). Ideal value:

0 LSB.

IIL

VCC/2

CS/H = 14pF

IIH

ADCn

1 to 100kΩ

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Figure 17-9. Offset Error

●Gain Error: After adjusting for offset, the gain error is found as the deviation of the last transition (0x3FE to 0x3FF)

compared to the ideal transition (at 1.5 LSB below maximum). Ideal value: 0 LSB

Figure 17-10. Gain Error

Offset

Error

Output Code

Ideal ADC

Actual ADC

REF

Input Voltage

Output Code

Ideal ADC

Actual ADC

REF

Input Voltage

Gain

Error

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●Integral non-linearity (INL): After adjusting for offset and gain error, the INL is the maximum deviation of an actual

transition compared to an ideal transition for any code. Ideal value: 0 LSB.

Figure 17-11. Integral Non-linearity (INL)

●Differential non-linearity (DNL): The maximum deviation of the actual code width (the interval between two adjacent

transitions) from the ideal code width (1 LSB). Ideal value: 0 LSB.

Figure 17-12. Differential Non-linearity (DNL)

●Quantization error: Due to the quantization of the input voltage into a finite number of codes, a range of input voltages

(1 LSB wide) will code to the same value. Always ±0.5 LSB.

●Absolute accuracy: The maximum deviation of an actual (unadjusted) transition compared to an ideal transition for

any code. This is the compound effect of offset, gain error, differential error, non-linearity, and quantization error. Ideal

value: ±0.5 LSB.

Output Code

Ideal ADC

INL

Actual ADC

REF

Input Voltage

Output Code

0x3FF

0x000

1 LSB

DNL

REF

Input Voltage

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17.8 ADC Conversion Result

After the conversion is complete (ADIF is high), the conversion result can be found in the ADC result registers (ADCL,

ADCH). The form of the conversion result depends on the type of the conversion as there are three types of conversions:

single ended conversion, unipolar differential conversion and bipolar differential conversion.

17.8.1 Single Ended Conversion

For single ended conversion, the result is:

where VIN is the voltage on the selected input pin and VREF the selected voltage reference (see Table 17-4 on page 188 and

Table 17-5 on page 189). 0x000 represents analog ground, and 0x3FF represents the selected voltage reference minus one

LSB. The result is presented in one-sided form, from 0x3FF to 0x000.

17.8.2 Unipolar Differential Conversion

If differential channels and an unipolar input mode are used, the result is:

where VPOS is the voltage on the positive input pin, VNEG the voltage on the negative input pin, and VREF the selected voltage

reference (see Table 17-4 on page 188 and Table 17-5 on page 189). The voltage on the positive pin must always be larger

than the voltage on the negative pin or otherwise the voltage difference is saturated to zero. The result is presented in one-

sided form, from 0x000 (0d) to 0x3FF (+1023d). The GAIN is either 8x or 20x.

17.8.3 Bipolar Differential Conversion

As default the ADC converter operates in the unipolar input mode, but the bipolar input mode can be selected by writing the

BIN bit in the ADCSRB register to one. In the bipolar input mode two-sided voltage differences are allowed and thus the

voltage on the negative input pin can also be larger than the voltage on the positive input pin. If differential channels and a

bipolar input mode are used, the result is:

where VPOS is the voltage on the positive input pin, VNEG the voltage on the negative input pin, and VREF the selected voltage

reference. The result is presented in two’s complement form, from 0x200 (–512d) through 0x000 (+0d) to 0x1FF (+511d). The

GAIN is either 8x or 20x.

However, if the signal is not bipolar by nature (9 bits + sign as the 10th bit), this scheme loses one bit of the converter

dynamic range. Then, if the user wants to perform the conversion with the maximum dynamic range, the user can perform a

quick polarity check of the result and use the unipolar differential conversion with selectable differential input pair. When the

polarity check is performed, it is sufficient to read the MSB of the result (ADC9 in ADCH register). If the bit is one, the result

is negative, and if this bit is zero, the result is positive.

ADC VIN 1024

VREF

---------------------------

ADC VPOS VNEG

–1024

VREF

-------------------------------------------------------GAIN=

ADC VPOS VNEG

–512

VREF

----------------------------------------------------GAIN=

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17.9 Temperature Measurement

The temperature measurement is based on an on-chip temperature sensor that is coupled to a single ended ADC input.

MUX[4..0] bits in ADMUX register enables the temperature sensor. The internal 1.1V voltage reference must also be

selected for the ADC voltage reference source in the temperature sensor measurement. When the temperature sensor is

enabled, the ADC converter can be used in single conversion mode to measure the voltage over the temperature sensor.

The measured voltage has a linear relationship to the temperature as described in Table 17-2 on page 187. The voltage

sensitivity is approximately 1 LSB/°C and the accuracy of the temperature measurement is ±10°C using manufacturing

calibration values (TS_GAIN, TS_OFFSET). The values described in Table 17-2 on page 187 are typical values. However,

due to the process variation the temperature sensor output varies from one chip to another.

17.9.1 Manufacturing Calibration

Calibration values determined during test are available in the signature row.

The temperature in degrees celsius can be calculated using the formula:

Where:

a. ADCH and ADCL are the ADC data registers,

b. is the temperature sensor gain

c. TSOFFSET is the temperature sensor offset correction term

TS_GAIN is the unsigned fixed point 8-bit temperature sensor gain factor in 1/128th units stored in the signature

row

TS_OFFSET is the signed twos complement temperature sensor offset reading stored in the signature row. See

Table 20-1 on page 204 for signature row parameter address.

The following code example allows to read signature row data:

.equ TS_GAIN = 0x0007

.equ TS_OFFSET = 0x0005

LDI R30,LOW(TS_GAIN)

LDI R31,HIGH (TS_GAIN)

RCALL Read_signature_row

MOV R17,R16; Save R16 result

LDI R30,LOW(TS_OFFSET)

LDI R31,HIGH (TS_OFFSET)

RCALL Read_signature_row

; R16 holds TS_OFFSET and R17 holds TS_GAIN

Read_signature_row:

IN R16,SPMCSR ; Wait for SPMEN ready

SBRC R16,SPMEN ; Exit loop here when SPMCSR is free

RJMP Read_signature_row

LDI R16,((1<<SIGRD)|(1<<SPMEN)); We need to set SIGRD and SPMEN

together

OUT SPMCSR,R16 ; and execute the LPM within 3 cycles

LPM R16,Z

RET

Table 17-2. Temperature versus Sensor Output Voltage (Typical Case): Example ADC Values

Temperature/°C –40°C +25°C +85°C

0x00F6 0x0144 0c01B8

TADCH 8«ADCL273 25 TS_OFFSET–+–128

TS_GAIN

------------------------------------------------------------------------------------------------------------------------------------------------ 25+=

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17.10 Internal Voltage Reference Output

The internal voltage reference is output on XREF pin as described in Table 17-3 on page 188 if the ADC is turned on (see

Section 6.2.1 “Voltage Reference Enable Signals and Start-up Time” on page 51). Addition of an external filter capacitor

(5 to 10nF) on XREF pin may be necessary. XREF current load must be from 1µA to 100µA with VCC from 2.7V to 5.5V for

XREF = 1.1V and with VCC from 4.5V to 5.5V for XREF = 2.56V.

XREF pin can be coupled to an analog input of the ADC (see Section 1.6 “Pin Configuration” on page 6).

17.11 Register Description

17.11.1 ADMUX – ADC Multiplexer Selection Register

• Bit 7:6 – REFS1:REFS0: Voltage Reference Selection Bits

These bits and AREFEN bit from the analog miscellaneous control register (AMISCR) select the voltage reference for the

ADC, as shown in Table 17-4. If these bits are changed during a conversion, the change will not go in effect until this

conversion is complete (ADIF in ADCSRA register is set). Whenever these bits are changed, the next conversion will take 25

ADC clock cycles. If active channels are used, using AVCC or an external AREF higher than (AVcc – 1V) is not

recommended, as this will affect ADC accuracy. The internal voltage reference options may not be used if an external

voltage is being applied to the AREF pin.

• Bit 5 – ADLAR: ADC Left Adjust Result

The ADLAR bit affects the presentation of the ADC conversion result in the ADC data register. Write one to ADLAR to left

adjust the result. Otherwise, the result is right adjusted. Changing the ADLAR bit will affect the ADC data register

immediately, regardless of any ongoing conversions. For a complete description of this bit, see Section 17.11.3 “ADCL and

ADCH – The ADC Data Register” on page 191.

Table 17-3. Internal Voltage Reference Output

XREFEN (1) REFS1 (2) REFS0 (2) Voltage Reference Output (Iload ≤ 100 µA)

0 x x Hi-Z, the pin can be used as AREF input or other alternate functions.

1 (1) 0 1 XREF = 1.1V (3)

1 (1) 1 1 XREF = 2.56V (3)(4)

Notes: 1. See “Bit 1 – XREFEN: Internal Voltage Reference Output Enable” on page 193

2. See “Bit 7:6 – REFS1:REFS0: Voltage Reference Selection Bits” on page 188

3. In these configurations, the pin pull-up must be turned off and the pin digital output must be set in Hi-Z.

4. Vcc in range 4.5 - 5.5V.

Bit 76543210

REFS1 REFS0 ADLAR MUX4 MUX3 MUX2 MUX1 MUX0 ADMUX

Read/Write R/W R/W R/W R/W R/W R/W R/W R/W

Initial Value00000000

Table 17-4. Voltage Reference Selections for ADC

REFS1 REFS0 AREFEN Voltage Reference (VREF) Selection

X 0 0 AVcc used as voltage reference, diconnected from AREF pin.

X 0 1 External voltage reference at AREF pin (AREF ≥ 2.0V)

0 1 0 Internal 1.1V voltage reference

1 1 0 Internal 2.56V voltage reference

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• Bits 4:0 – MUX4:0: Analog Channel and Gain Selection Bits

These bits select which combination of analog inputs are connected to the ADC. In case of differential input, gain selection is

also made with these bits. Refer to Table 17-5 on page 189 for details. If these bits are changed during a conversion, the

change will not go into effect until this conversion is complete (ADIF in ADCSRA register is set).

Table 17-5. Input Channel Selections

MUX[4..0] Single Ended Input

Positive Differential

Input

Negative Differential

Input Gain

0 0000 ADC0 (PA0)

NA NA NA

0 0001 ADC1 (PA1)

0 0010 ADC2 (PA2)

0 0011 ADC3 / ISRC (PA3)

0 0100 ADC4 (PA4)

0 0101 ADC5 (PA5)

0 0110 ADC6 (PA6)

0 0111 ADC7 / AREF (PA7)

0 1000 ADC8 (PB5)

0 1001 ADC9 (PB6)

0 1010 ADC10 (PB7)

0 1011 Temperature Sensor

0 1100 Bandgap Reference (1.1 V)

0 1101 AVcc/4

0 1110 GND (0V)

0 1111 (reserved)

1 0000

N/A

ADC0 (PA0) ADC1 (PA1) 8x

1 0001 20x

1 0010 ADC1 (PA1) ADC2 (PA2) 8x

1 0011 20x

1 0100 ADC2 (PA2) ADC3 (PA3) 8x

1 0101 20x

1 0110 ADC4 (PA4) ADC5 (PA5) 8x

1 0111 20x

1 1000 ADC5 (PA5) ADC6 (PA6) 8x

1 1001 20x

1 1010 ADC6 (PA6) ADC7 (PA7) 8x

1 1011 20x

1 1100 ADC8 (PB5) ADC9 (PB6) 8x

1 1101 20x

1 1110 ADC9 (PB6) ADC10 (PB7) 8x

1 1111 20x

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17.11.2 ADCSRA – ADC Control and Status Register A

• Bit 7 – ADEN: ADC Enable

Writing this bit to one enables the ADC. By writing it to zero, the ADC is turned off. Turning the ADC off while a conversion is

in progress, will terminate this conversion.

• Bit 6 – ADSC: ADC Start Conversion

In single conversion mode, write this bit to one to start each conversion. In free running mode, write this bit to one to start the

first conversion. The first conversion after ADSC has been written after the ADC has been enabled, or if ADSC is written at

the same time as the ADC is enabled, will take 25 ADC clock cycles instead of the normal 13. This first conversion performs

initialization of the ADC.

ADSC will read as one as long as a conversion is in progress. When the conversion is complete, it returns to zero. Writing

zero to this bit has no effect.

• Bit 5 – ADATE: ADC Auto Trigger Enable

When this bit is written to one, auto triggering of the ADC is enabled. The ADC will start a conversion on a positive edge of

the selected trigger signal. The trigger source is selected by setting the ADC trigger select bits, ADTS in ADCSRB.

• Bit 4 – ADIF: ADC Interrupt Flag

This bit is set when an ADC conversion completes and the data registers are updated. The ADC conversion complete

interrupt is executed if the ADIE bit and the I-bit in SREG are set. ADIF is cleared by hardware when executing the

corresponding interrupt handling vector. Alternatively, ADIF is cleared by writing a logical one to the flag. Beware that if

doing a read-modify-write on ADCSRA, a pending interrupt can be disabled. This also applies if the SBI and CBI instructions

are used.

• Bit 3 – ADIE: ADC Interrupt Enable

When this bit is written to one and the I-bit in SREG is set, the ADC conversion complete interrupt is activated.

• Bits 2:0 – ADPS2:0: ADC Prescaler Select Bits

These bits determine the division factor between the system clock frequency and the input clock to the ADC.

Bit 76543210

ADEN ADSC ADATE ADIF ADIE ADPS2 ADPS1 ADPS0 ADCSRA

Read/Write R/W R/W R/W R/W R/W R/W R/W R/W

Initial Value 0 0 0 0 0 0 0 0

Table 17-6. ADC Prescaler Selections

ADPS2 ADPS1 ADPS0 Division Factor

0 0 0 2

0 0 1 2

0 1 0 4

0 1 1 8

1 0 0 16

1 0 1 32

1 1 0 64

1 1 1 128

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17.11.3 ADCL and ADCH – The ADC Data Register

17.11.3.1 ADLAR = 0

17.11.3.2 ADLAR = 1

When an ADC conversion is complete, the result is found in these two registers.

When ADCL is read, the ADC data register is not updated until ADCH is read. Consequently, if the result is left adjusted and

no more than 8-bit precision is required, it is sufficient to read ADCH. Otherwise, ADCL must be read first, then ADCH.

The ADLAR bit in ADMUX, and the MUXn bits in ADMUX affect the way the result is read from the registers. If ADLAR is set,

the result is left adjusted. If ADLAR is cleared (default), the result is right adjusted.

• ADC9:0: ADC Conversion Result

These bits represent the result from the conversion, as detailed in Section 17.8 “ADC Conversion Result” on page 186.

17.11.4 ADCSRB – ADC Control and Status Register B

• Bit 7– BIN: Bipolar Input Mode

The gain stage is working in the unipolar mode as default, but the bipolar mode can be selected by writing the BIN bit in the

ADCSRB register. In the unipolar mode only one-sided conversions are supported and the voltage on the positive input must

always be larger than the voltage on the negative input. Otherwise the result is saturated to the voltage reference. In the

bipolar mode two-sided conversions are supported and the result is represented in the two’s complement form. In the

unipolar mode the resolution is 10 bits and the bipolar mode the resolution is 9 bits + 1 sign bit.

• Bit 3 – Res: Reserved Bit

This bit is reserved for future use. For compatibility with future devices it must be written to zero when ADCSRB register is

written.

Bit 15 14 13 12 11 10 9 8

– – – – – – ADC9 ADC8 ADCH

ADC7 ADC6 ADC5 ADC4 ADC3 ADC2 ADC1 ADC0 ADCL

76543210

Read/Write R R R R R R R R

RRRRRRRR

Initial Value 0 0 0 0 0 0 0 0

00000000

Bit 15 14 13 12 11 10 9 8

ADC9 ADC8 ADC7 ADC6 ADC5 ADC4 ADC3 ADC2 ADCH

ADC1 ADC0 – – – – – – ADCL

76543210

Read/Write R R R R R R R R

RRRRRRRR

Initial Value 0 0 0 0 0 0 0 0

00000000

Bit 76543210

BIN ACME ACIR1 ACIR0 – ADTS2 ADTS1 ADTS0 ADCSRB

Read/Write R/W R/W R/W R/W R R/W R/W R/W

Initial Value00000000

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• Bits 2:0 – ADTS2:0: ADC Auto Trigger Source

If ADATE in ADCSRA register is written to one, the value of these bits selects which source will trigger an ADC conversion.

If ADATE is cleared, the ADTS2:0 settings will have no effect. A conversion will be triggered by the rising edge of the

selected interrupt flag. Note that switching from a trigger source that is cleared to a trigger source that is set, will generate a

positive edge on the trigger signal. If ADEN in ADCSRA register is set, this will start a conversion. Switching to free running

mode (ADTS[2:0]=0) will not cause a trigger event, even if the ADC interrupt flag is set.

17.11.5 DIDR0 – Digital Input Disable Register 0

• Bits 7:0 – ADC7D:ADC0D: ADC7:0 Digital Input Disable

When this bit is written logic one, the digital input buffer on the corresponding ADC pin is disabled. The corresponding PIN

register bit will always read as zero when this bit is set. When an analog signal is applied to the ADC7:0 pin and the digital

input from this pin is not needed, this bit should be written logic one to reduce power consumption in the digital input buffer.

17.11.6 DIDR1 – Digital Input Disable Register 1

• Bit 7 – Res: Reserved Bit

This bit is reserved for future use. For compatibility with future devices it must be written to zero when DIDR1 register is

written.

• Bits 6..4 – ADC10D..ADC8D: ADC10..8 Digital Input Disable

When this bit is written logic one, the digital input buffer on the corresponding ADC pin is disabled. The corresponding PIN

register bit will always read as zero when this bit is set. When an analog signal is applied to the ADC10:8 pin and the digital

input from this pin is not needed, this bit should be written logic one to reduce power consumption in the digital input buffer.

• Bits 3:0 - Reserved Bits

These bits are reserved for future use. For compatibility with future devices, they must be written to zero when DIDR1 is

written.

Table 17-7. ADC Auto Trigger Source Selections

ADTS2 ADTS1 ADTS0 Trigger Source

000Free running mode

001Analog comparator

010External interrupt request 0

011Timer/counter1 compare match A

100Timer/counter1 overflow

101Timer/counter1 compare match B

110Timer/counter1 capture event

111Watchdog interrupt request

Bit 76543210

ADC7D /

AIN1D

ADC6D /

AIN0D ADC5D ADC4D ADC3D ADC2D ADC1D ADC0D DIDR0

Read/Write R/W R/W R/W R/W R/W R/W R/W R/W

Initial Value00000000

Bit 76543210

- ADC10D ADC9D ADC8D ---- DIDR1

Read/Write R R/W R/W R/W R R R R

Initial Value00000000

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17.11.7 AMISCR – Analog Miscellaneous Control Register

• Bits 7:3 – Reserved Bits

These bits are reserved for future use. For compatibility with future devices, they must be written to zero when AMISCR is

written.

• Bit 2 – AREFEN: External Voltage Reference Input Enable

When this bit is written logic one, the voltage reference for the ADC is input from AREF pin as described in Table 17.10 on

page 188. If active channels are used, using AVcc or an external AREF higher than (AVcc - 1V) is not recommended, as this

will affect ADC accuracy. The internal voltage reference options may not be used if an external voltage is being applied to

the AREF pin. It is recommended to use DIDR register bit function (digital input disable) when AREFEN is set.

• Bit 1 – XREFEN: Internal Voltage Reference Output Enable

When this bit is written logic one, the internal voltage reference 1.1V or 2.56V is output on XREF pin as described in Table

17.10 on page 188. It is recommended to use DIDR register bit function (digital input disable) when XREFEN is set.

Bit 76543210

-----AREFENXREFEN

ISRCEN AMISCR

Read/Write RRRRRR/WR/WR/W

Initial Value00000000

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18. AnaComp - Analog Comparator

The analog comparator compares the input values on the positive pin (AIN1) and negative pin (AIN0). When the voltage on

the positive pin is higher than the voltage on the negative pin, the analog comparator output, ACO, is set. The comparator

can trigger a separate interrupt, exclusive to the analog comparator. The user can select interrupt triggering on comparator

output rise, fall or toggle. A block diagram of the comparator and its surrounding logic is shown in Figure 18-1.

Figure 18-1. Analog Comparator Block Diagram(1)(2)

Notes: 1. See Table 18-2 on page 196 and Table 18-3 on page 197

2. Refer to Figure 1-2 on page 6 and Table 9-3 on page 73 for analog comparator pin placement.

18.1 Register Description

18.1.1 ADC Control and Status Register B – ADCSRB

• Bit 6 – ACME: Analog Comparator Multiplexer Enable

When this bit is written logic one and the ADC is switched off (ADEN in ADCSRA is zero), the ADC multiplexer selects the

positive input to the analog comparator. When this bit is written logic zero, AIN1 is applied to the positive input of the analog

comparator.

When the analog to digital converter (ADC) is configured as single ended input channel, it is possible to select any of the

ADC[10..0] pins to replace the positive input to the analog comparator. The ADC multiplexer (MUX[4..0]) is used to select

this input, and consequently, the ADC must be switched off to utilize this feature.

Interrupt

Sensivity

Control

Internal

2.56V

Reference

AIN1

(PA7)

AVCC

ACIS1

DC Multiplexer

Output(1)

(from ADC)

ADEN

ACIS0

ACI

ACIE

16-bit Timer/ Counter

Input Capture

Analog Comparator

Interrupt

ACME

2.56V

1.28V

0.64V

0.32V

ACIRS

ACD

REFS0

REFS1

ACIR0

ACIR1

ACO

AIN0

(PA6)

Bit 7 6543210

BIN ACME ACIR1 ACIR0 —ADTS2 ADTS1 ADTS0 ADCSRB

Read/Write R R/W R/W R/W R R/W R/W R/W

Initial Value0 0000000

Note: When changing the A IS1/ACISU hits. the Analog Comparator Inkerrupk must be disabled by clearing its inter- AtmeL

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• Bits 5, 4 – ACIR1, ACIR0: Analog Comparator Internal Voltage Reference Select

When ACIRS bit is set in ADCSRA register, these bits select a voltage reference for the negative input to the analog

comparator, see Table 18-3 on page 197.

18.1.2 ACSR – Analog Comparator Control and Status Register

• Bit 7 – ACD: Analog Comparator Disable

When this bit is written logic one, the power to the analog comparator is switched off. This bit can be set at any time to turn

off the analog comparator. This will reduce power consumption in active and idle mode. When changing the ACD bit, the

analog comparator interrupt must be disabled by clearing the ACIE bit of ACSR register. Otherwise an interrupt can occur

when the bit is changed.

• Bit 6 – ACIRS: Analog Comparator Internal Reference Select

When this bit is set an internal reference voltage replaces the negative input to the analog comparator (c.f. Table 18-3 on

page 197). If ACIRS is cleared, AIN0 is applied to the negative input to the analog comparator.

• Bit 5 – ACO: Analog Comparator Output

The output of the analog comparator is synchronized and then directly connected to ACO. The synchronization introduces a

delay of 1 - 2 clock cycles.

• Bit 4 – ACI: Analog Comparator Interrupt Flag

This bit is set by hardware when a comparator output event triggers the interrupt mode defined by ACIS1 and ACIS0. The

analog comparator interrupt routine is executed if the ACIE bit is set and the I-bit in SREG is set. ACI is cleared by hardware

when executing the corresponding interrupt handling vector. Alternatively, ACI is cleared by writing a logic one to the flag.

• Bit 3 – ACIE: Analog Comparator Interrupt Enable

When the ACIE bit is written logic one and the I-bit in the status register is set, the analog comparator interrupt is activated.

When written logic zero, the interrupt is disabled.

• Bit 2 – ACIC: Analog Comparator Input Capture Enable

When written logic one, this bit enables the input capture function in Timer/counter1 to be triggered by the analog

comparator. The comparator output is in this case directly connected to the input capture front-end logic, making the

comparator utilize the noise canceler and edge select features of the Timer/counter1 Input capture interrupt. When written

logic zero, no connection between the analog comparator and the input capture function exists. To make the comparator

trigger the Timer/counter1 input capture interrupt, the ICIE1 bit in the timer interrupt mask register (TIMSK1) must be set.

• Bits 1, 0 – ACIS1, ACIS0: Analog Comparator Interrupt Mode Select

These bits determine which comparator events that trigger the analog comparator interrupt. The different settings are shown

in Table 18-1.

Bit 76543210

ACD ACIRS ACO ACI ACIE ACIC ACIS1 ACIS0 ACSR

Read/Write R/W R/W R R/W R/W R/W R/W R/W

Initial Value00N/A00000

Table 18-1. ACIS1 / ACIS0 Settings

ACIS1 ACIS0 Interrupt Mode

0 0 Comparator interrupt on output toggle.

0 1 Reserved

1 0 Comparator interrupt on falling output edge.

1 1 Comparator interrupt on rising output edge.

Note: When changing the ACIS1/ACIS0 bits, the Analog Comparator Interrupt must be disabled by clearing its inter-

rupt enable bit in the ACSR register. Otherwise an interrupt can occur when the bits are changed.

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18.1.3 DIDR0 – Digital Input Disable Register 0

• Bits 7,6 – AIN1D, AIN0D: AIN1D and AIN0D Digital Input Disable

When this bit is written logic one, the digital input buffer on the corresponding analog compare pin is disabled. The

corresponding PIN register bit will always read as zero when this bit is set. When an analog signal is applied to the AIN0/1

pin and the digital input from this pin is not needed, this bit should be written logic one to reduce power consumption in the

digital input buffer.

18.2 Analog Comparator Inputs

18.2.1 Analog Compare Positive Input

It is possible to select any of the inputs of the ADC positive input multiplexer to replace the positive input to the analog

comparator. The ADC multiplexer is used to select this input, and consequently, the ADC must be switched off to utilize this

feature. If the analog comparator multiplexer enable bit (ACME in ADCSRB register) is set and the ADC is switched off

(ADEN in ADCSRA register is zero), MUX[4..0] in ADMUX register select the input pin to replace the positive input to the

analog comparator, as shown in Table 18-2 on page 196. If ACME is cleared or ADEN is set, AIN1 pin is applied to the

positive input to the analog comparator.

Bit 76543210

ADC7D /

AIN1D

ADC6D /

AIN0D ADC5D ADC4D ADC3D ADC2D ADC1D ADC0D DIDR0

Read/Write R/W R/W R/W R/W R/W R/W R/W R/W

Initial Value00000000

Table 18-2. Analog Comparator Positive Input

ACME ADEN MUX[4..0] Analog Comparator Positive Input - Comment

0 x x xxxx b AIN1 ADC Switched On

x 1 x xxxx b AIN1

1 0 0 0000 b ADC0

ADC Switched Off.

1 0 0 0001 b ADC1

1 0 0 0010 b ADC2

1 0 0 0011 b ADC3 / ISRC

1 0 0 0100 b ADC4

1 0 0 0101 b ADC5

1 0 0 0110 b ADC6

1 0 0 0111 b ADC7

1 0 0 1000 b ADC8

1 0 0 1001 b ADC9

1 0 0 1010 b ADC10

1 0 Other This doesn’t make sense - Don’t use.

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18.2.2 Analog Compare Negative Input

It is possible to select an internal voltage reference to replace the negative input to the analog comparator. The output of a 2-

bit DAC using the internal voltage reference of the DAC is available when ACIRS bit of ACSR register is set. The voltage

reference division factor is done by ACIR[1..0] of ADCSRB register.

If ACIRS is cleared, AIN0 pin is applied to the negative input to the analog comparator.

Table 18-3. Analog Comparator Negative Input

ACIRS ACIR[1..0] REFS[1..0] Analog Comparator Negative Input - Comment

0 x x AIN0

1 x

0 0 b

0 1 b

1 0 b

Reserved

10 0 b 1 1 b 2.56 V - using internal 2.56V voltage reference

10 1 b 1 1 b 1.28 V (1/2 of 2.56V) - using internal 2.56V voltage reference

11 0 b 1 1 b 0.64 V (1/4 of 2.56V - using internal 2.56V voltage reference

11 1 b 1 1 b 0.32 V (1/8 of 2.56V) - using internal 2.56V voltage reference

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19. DebugWIRE On-chip Debug System

19.1 Features

●Complete program flow control

●Emulates all on-chip functions, both digital and analog, except RESET pin

●Real-time operation

●Symbolic debugging support (both at C and assembler source level, or for other HLLs)

●Unlimited number of program break points (using software break points)

●Non-intrusive operation

●Electrical characteristics identical to real device

●Automatic configuration system

●High-speed operation

●Programming of non-volatile memories

19.2 Overview

The debugWIRE on-chip debug system uses a One-wire, bi-directional interface to control the program flow, execute AVR®

instructions in the CPU and to program the different non-volatile memories.

19.3 Physical Interface

When the debugWIRE enable (DWEN) fuse is programmed and lock bits are unprogrammed, the debugWIRE system within

the target device is activated. The RESET port pin is configured as a wire-AND (open-drain) bi-directional I/O pin with pull-up

enabled and becomes the communication gateway between target and emulator.

Figure 19-1. The debugWIRE Setup

Figure 19-1 shows the schematic of a target MCU, with debugWIRE enabled, and the emulator connector. The system clock

is not affected by debugWIRE and will always be the clock source selected by the CKSEL fuses.

When designing a system where debugWIRE will be used, the following observations must be made for correct operation:

●Pull-up resistors on the dW/(RESET) line must not be smaller than 10k. The pull-up resistor is not required for

debugWIRE functionality.

●Connecting the RESET pin directly to Vcc will not work.

●Capacitors connected to the RESET pin must be disconnected when using debugWire.

●All external reset sources must be disconnected.

GND

dW (RESET)

VCC

+1.8 to +5.5V

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19.4 Software Break Points

DebugWIRE supports program memory break points by the AVR® BREAK instruction. Setting a break point in Atmel® AVR

Studio® will insert a BREAK instruction in the program memory. The instruction replaced by the BREAK instruction will be

stored. When program execution is continued, the stored instruction will be executed before continuing from the program

memory. A break can be inserted manually by putting the BREAK instruction in the program.

The flash must be re-programmed each time a break point is changed. This is automatically handled by AVR Studio through

the debugWIRE interface. The use of break points will therefore reduce the flash data retention. Devices used for debugging

purposes should not be shipped to end customers.

19.5 Limitations of DebugWIRE

The debugWIRE communication pin (dW) is physically located on the same pin as external reset (RESET). An external reset

source is therefore not supported when the debugWIRE is enabled.

The debugWIRE system accurately emulates all I/O functions when running at full speed, i.e., when the program in the CPU

is running. When the CPU is stopped, care must be taken while accessing some of the I/O registers via the debugger (AVR

Studio).

A programmed DWEN fuse enables some parts of the clock system to be running in all sleep modes. This will increase the

power consumption while in sleep. Thus, the DWEN Fuse should be disabled when debugWire is not used.

19.6 DebugWIRE Related Register in I/O Memory

The following section describes the registers used with the debugWire.

19.6.1 DebugWIRE Data Register – DWDR

The DWDR register provides a communication channel from the running program in the MCU to the debugger. This register

is only accessible by the debugWIRE and can therefore not be used as a general purpose register in the normal operations.

Bit 76543210

DWDR[7:0] DWDR

Read/Write R/W R/W R/W R/W R/W R/W R/W R/W

Initial Value00000000

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20. Flash Programming

The device provides a self-programming mechanism for downloading and uploading program code by the MCU itself. The

self-programming can use any available data interface (i.e. LIN, USART, ...) and associated protocol to read code and write

(program) that code into the program memory.

The program memory is updated in a page by page fashion. Before programming a page with the data stored in the

temporary page buffer, the page must be erased. The temporary page buffer is filled one word at a time using SPM and the

buffer can be filled either before the page erase command or between a page erase and a page write operation:

●Alternative 1, fill the buffer before a page erase

●Fill temporary page buffer

●Perform a page erase

●Perform a page write

●Alternative 2, fill the buffer after page erase

●Perform a page erase

●Fill temporary page buffer

●Perform a page write

If only a part of the page needs to be changed, the rest of the page must be stored (for example in the temporary page

buffer) before the erase, and then be re-written. When using alternative 1, the boot loader provides an effective read-modify-

write feature which allows the user software to first read the page, do the necessary changes, and then write back the

modified data. If alternative 2 is used, it is not possible to read the old data while loading since the page is already erased.

The temporary page buffer can be accessed in a random sequence. It is essential that the page address used in both the

page erase and page write operation is addressing the same page.

20.1 Self-programming the Flash

20.1.1 Performing Page Erase by SPM

To execute page erase, set up the address in the Z-pointer, write “00000011 b” to SPMCSR and execute SPM within four

clock cycles after writing SPMCSR. The data in R1 and R0 is ignored. The page address must be written to PCPAGE in the

Z-register. Other bits in the Z-pointer will be ignored during this operation.

●The CPU is halted during the page erase operation.

20.1.2 Filling the Temporary Buffer (Page Loading)

To write an instruction word, set up the address in the Z-pointer and data in R1:R0, write “00000001b” to SPMCSR and

execute SPM within four clock cycles after writing SPMCSR. The content of PCWORD in the Z-register is used to address

the data in the temporary buffer. The temporary buffer will auto-erase after a page write operation or by writing the CTPB bit

in SPMCSR. It is also erased after a system reset. Note that it is not possible to write more than one time to each address

without erasing the temporary buffer.

If the EEPROM is written in the middle of an SPM page load operation, all data loaded will be lost.

20.1.3 Performing a Page Write

To execute page write, set up the address in the Z-pointer, write “00000101 b” to SPMCSR and execute SPM within four

clock cycles after writing SPMCSR. The data in R1 and R0 is ignored. The page address must be written to PCPAGE. Other

bits in the Z-pointer must be written to zero during this operation.

●The CPU is halted during the Page Write operation.

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20.2 Addressing the Flash During Self-programming

The Z-pointer is used to address the SPM commands. The Z pointer consists of the Z-registers ZL and ZH in the register file.

The number of bits actually used is implementation dependent.

Since the flash is organized in pages (see Table 21-7 on page 210), the program counter can be treated as having two

different sections. One section, consisting of the least significant bits, is addressing the words within a page, while the most

significant bits are addressing the pages. This is shown in Figure 20-1.

Note that the page erase and page write operations are addressed independently. Therefore it is of major importance that

the software addresses the same page in both the page erase and page write operation.

The LPM instruction uses the Z-pointer to store the address. Since this instruction addresses the flash byte-by-byte, also the

LSB (bit Z0) of the Z-pointer is used.

Figure 20-1. Addressing the Flash During SPM (1)

Note: 1. The different variables used in Table 20-2 on page 204 are listed in Table 21-7 on page 210.

Bit 151413121110 9 8

Z15 Z14 Z13 Z12 Z11 Z10 Z9 Z8 ZH (R31)

Z7 Z6 Z5 Z4 Z3 Z2 Z1 Z0 ZL (R30)

Bit76543210

PAGEMSBPCMSB

ZPCMSB15 1 0

0 Z-POINTER

BIT ZPAGEMSB

WORD ADDRESS

WITHIN A PAGE

PAGE ADDRESS

WITHIN THE FLASH

PCWORDPCPAGE

PAGE INSTRUCTION WORD

PROGRAM MEMORY PAGE

PROGRAM COUNTER

PAGEEND

PCWORD [PAGEMSB : 0]

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20.2.1 Store Program Memory Control and Status Register – SPMCSR

The store program memory control and status register contains the control bits needed to control the boot loader operations.

• Bit 7 – Res: Reserved Bit

This bit is a reserved bit in the Atmel® ATtiny87/167 and will always read as zero.

• Bit 6 – RWWSB: Read-While-Write Section Busy

This bit is for compatibility with devices supporting read-while-write. It will always read as zero in Atmel ATtiny87/167.

• Bit 5 – SIGRD: Signature Row Read

If this bit is written to one at the same time as SPMEN, the next LPM instruction within three clock cycles will read a byte from

the signature row into the destination register. See Section 20.2.4 “Reading the Signature Row from Software” on page 204

for details. An SPM instruction within four cycles after SIGRD and SPMEN are set will have no effect.

• Bit 4 – CTPB: Clear Temporary Page Buffer

If the CTPB bit is written while filling the temporary page buffer, the temporary page buffer will be cleared and the data will be

lost.

• Bit 3 – RFLB: Read Fuse and Lock Bits

An LPM instruction within three cycles after RFLB and SPMEN are set in the SPMCSR register, will read either the lock bits

or the fuse bits (depending on Z0 in the Z-pointer) into the destination register. See Section 20.2.3 “Reading the Fuse and

Lock Bits from Software” on page 203 for details.

• Bit 2 – PGWRT: Page Write

If this bit is written to one at the same time as SPMEN, the next SPM instruction within four clock cycles executes page write,

with the data stored in the temporary buffer. The page address is taken from the high part of the Z-pointer. The data in R1

and R0 are ignored. The PGWRT bit will auto-clear upon completion of a page write, or if no SPM instruction is executed

within four clock cycles. The CPU is halted during the entire page write operation.

• Bit 1 – PGERS: Page Erase

If this bit is written to one at the same time as SPMEN, the next SPM instruction within four clock cycles executes page

erase. The page address is taken from the high part of the Zpointer. The data in R1 and R0 are ignored. The PGERS bit will

auto-clear upon completion of a page erase, or if no SPM instruction is executed within four clock cycles. The CPU is halted

during the entire page write operation.

• Bit 0 – SPMEN: Self Programming Enable

This bit enables the SPM instruction for the next four clock cycles. If written to one together with either SIGRD, CTPB, RFLB,

PGWRT, or PGERS, the following SPM instruction will have a special meaning, see description above. If only SPMEN is

written, the following SPM instruction will store the value in R1:R0 in the temporary page buffer addressed by the Z-pointer.

The LSB of the Z-pointer is ignored. The SPMEN bit will auto-clear upon completion of an SPM instruction, or if no SPM

instruction is executed within four clock cycles. During page erase and page write, the SPMEN bit remains high until the

operation is completed.

Writing any other combination than “10 0001 b”, “01 0001 b”, “00 1001 b”, “00 0101 b”, “00 0011 b” or “00 0001 b” in the lower

six bits will have no effect.

Note: Only one SPM instruction should be active at any time.

Bit7654321 0

–RWWSB SIGRD CTPB RFLB PGWRT PGERS SPMEN SPMCSR

Read/Write R R R R/W R/W R/W R/W R/W

Initial Value0000000 0

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20.2.2 EEPROM Write Prevents Writing to SPMCSR

Note that an EEPROM write operation will block all software programming to flash. Reading the fuses and lock bits from

software will also be prevented during the EEPROM write operation. It is recommended that the user checks the status bit

(EEPE) in the EECR register and verifies that the bit is cleared before writing to the SPMCSR register.

20.2.3 Reading the Fuse and Lock Bits from Software

It is possible to read both the fuse and lock bits from software. To read the lock bits, load the Z-pointer with 0x0001 and set

the RFLB and SPMEN bits in SPMCSR. When an LPM instruction is executed within three CPU cycles after the RFLB and

SPMEN bits are set in SPMCSR, the value of the lock bits will be loaded in the destination register. The RFLB and SPMEN

bits will auto-clear upon completion of reading the lock bits or if no LPM instruction is executed within three CPU cycles or no

SPM instruction is executed within four CPU cycles. When RFLB and SPMEN are cleared, LPM will work as described in the

instruction set manual.

The algorithm for reading the fuse low byte is similar to the one described above for reading the lock bits. To read the fuse

low byte, load the Z-pointer with 0x0000 and set the RFLB and SPMEN bits in SPMCSR. When an LPM instruction is

executed within three cycles after the RFLB and SPMEN bits are set in the SPMCSR, the value of the fuse low byte (FLB)

will be loaded in the destination register as shown below. See Table 21-5 on page 209 for a detailed description and mapping

of the fuse low byte.

Similarly, when reading the fuse high byte (FHB), load 0x0003 in the Z-pointer. When an LPM instruction is executed within

three cycles after the RFLB and SPMEN bits are set in the SPMCSR, the value of the fuse high byte will be loaded in the

destination register as shown below. See Table 21-4 on page 208 for detailed description and mapping of the fuse high byte.

Similarly, when reading the extended fuse byte (EFB), load 0x0002 in the Z-pointer. When an LPM instruction is executed

within three cycles after the RFLB and SPMEN bits are set in the SPMCSR, the value of the extended fuse byte will be

loaded in the destination register as shown below. See Table 21-3 on page 208 for detailed description and mapping of the

extended fuse byte.

Fuse and lock bits that are programmed, will be read as zero. Fuse and lock bits that are unprogrammed, will be read as

one.

Bit 76543210

Rd (Z=0x0001) – – – – – – LB2 LB1

Bit 76543210

Rd (Z=0x0000) FLB7 FLB6 FLB5 FLB4 FLB3 FLB2 FLB1 FLB0

Bit 76543210

Rd (Z=0x0003) FHB7 FHB6 FHB5 FHB4 FHB3 FHB2 FHB1 FHB0

Bit 76543210

Rd (Z=0x0002) – – – – – – – EFB0

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20.2.4 Reading the Signature Row from Software

To read the signature row from software, load the Z-pointer with the signature byte address given in Table 20-1 on page 204

and set the SIGRD and SPMEN bits in SPMCSR. When an LPM instruction is executed within three CPU cycles after the

SIGRD and SPMEN bits are set in SPMCSR, the signature byte value will be loaded in the destination register. The SIGRD

and SPMEN bits will auto-clear upon completion of reading the Signature Row Lock bits or if no LPM instruction is executed

within three CPU cycles. When SIGRD and SPMEN are cleared, LPM will work as described in the instruction set manual.

20.2.5 Preventing Flash Corruption

During periods of low Vcc, the flash program can be corrupted because the supply voltage is too low for the CPU and the

flash to operate properly. These issues are the same as for board level systems using the flash, and the same design

solutions should be applied.

A flash program corruption can be caused by two situations when the voltage is too low.

●First, a regular write sequence to the flash requires a minimum voltage to operate correctly.

●Secondly, the CPU itself can execute instructions incorrectly, if the supply voltage for executing instructions is too low.

Flash corruption can easily be avoided by following these design recommendations (one is sufficient):

1. Keep the AVR® RESET active (low) during periods of insufficient power supply voltage. This can be done by

enabling the internal brown-out detector (BOD) if the operating voltage matches the detection level. If not, an

external low Vcc reset protection circuit can be used. If a reset occurs while a write operation is in progress, the

write operation will be completed provided that the power supply voltage is sufficient.

2. Keep the AVR core in power-down sleep mode during periods of low Vcc. This will prevent the CPU from attempt-

ing to decode and execute instructions, effectively protecting the SPMCSR register and thus the flash from

unintentional writes.

20.2.6 Programming Time for Flash when Using SPM

The calibrated RC oscillator is used to time flash accesses. Table 20-2 shows the typical programming time for flash

accesses from the CPU.

Table 20-1. Signature Row Addressing

Signature Byte Z-Pointer Address

Device signature byte 0 0x0000

Device signature byte 1 0x0002

Device signature byte 2 0x0004

8MHz RC oscillator calibration byte 0x0001

TSOFFSET - temp sensor offset 0x0005

TSGAIN - temp sensor gain 0x0007

Note: All other addresses are reserved for future use.

Table 20-2. SPM Programming Time

Symbol Min Programming Time Max Programming Time

Flash write (page erase, page write, and write lock

bits by SPM) 3.7ms 4.5ms

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20.2.7 Simple Assembly Code Example for a Boot Loader

Note that the RWWSB bit will always be read as zero in Atmel® ATtiny87/167. Nevertheless, it is

recommended to check this bit as shown in the code example, to ensure compatibility with devices supporting read-while-

write.

;- The routine writes one page of data from RAM to Flash

; the first data location in RAM is pointed to by the Y-pointer

; the first data location in Flash is pointed to by the Z-pointer

;- Error handling is not included

;- Registers used: r0, r1, temp1 (r16), temp2 (r17), looplo (r24),

; loophi (r25), spmcsrval (r20)

; - Storing and restoring of registers is not included in the routine

; register usage can be optimized at the expense of code size

.equ PAGESIZEB = PAGESIZE*2 ; AGESIZEB is page size in BYTES, not words

.org SMALLBOOTSTART

Write_page:

; Page Erase

ldi spmcsrval, (1<<PGERS) | (1<<SELFPGEN)

rcall Do_spm

; Clear temporary page buffer

ldi spmcsrval, (1<<CPTB) | (1<<SELFPGEN)

rcall Do_spm

; Transfer data from RAM to Flash temporary page buffer

ldi looplo, low(PAGESIZEB) ; init loop variable

ldi loophi, high(PAGESIZEB) ; not required for PAGESIZEB<=256

Wrloop:

ld r0, Y+

ld r1, Y+

ldi spmcsrval, (1<<SELFPGEN)

rcall Do_spm

adiw ZH:ZL, 2

sbiw loophi:looplo, 2 ; use subi for PAGESIZEB<=256

brne Wrloop

; Execute Page Write

subi ZL, low(PAGESIZEB) ; restore pointer

sbci ZH, high(PAGESIZEB) ; not required for PAGESIZEB<=256

ldi spmcsrval, (1<<PGWRT) | (1<<SELFPGEN)

rcall Do_spm

; Clear temporary page buffer

ldi spmcsrval, (1<<CPTB) | (1<<SELFPGEN)

rcall Do_spm

; Read back and check, optional

ldi looplo, low(PAGESIZEB) ; init loop variable

ldi loophi, high(PAGESIZEB) ; not required for PAGESIZEB<=256

subi YL, low(PAGESIZEB) ; restore pointer

sbci YH, high(PAGESIZEB)

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Rdloop:

lpm r0, Z+

ld r1, Y+

cpse r0, r1

rjmp Error

sbiw loophi:looplo, 1 ; use subi for PAGESIZEB<=256

brne Rdloop

; To ensure compatibility with devices supporting Read-While-Write

; Return to RWW section

; Verify that RWW section is safe to read

Return:

in temp1, SPMCSR

sbrs temp1, RWWSB ; If RWWSB is set, the RWW section is not ready yet

ret

; Clear temporary page buffer

ldi spmcsrval, (1<<CPTB) | (1<<SELFPGEN)

call Do_spm

rjmp Return

Do_spm:

; Check for previous SPM complete

Wait_spm:

in temp1, SPMCSR

sbrc temp1, SELFPGEN

rjmp Wait_spm

; Input: spmcsrval determines SPM action

; Disable interrupts if enabled, store status

in temp2, SREG

cli

; Check that no EEPROM write access is present

Wait_ee:

sbic EECR, EEPE

rjmp Wait_ee

; SPM timed sequence

out SPMCSR, spmcsrval

spm

; Restore SREG (to enable interrupts if originally enabled)

out SREG, temp2

ret

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21. Memory Programming

21.1 Program and Data Memory Lock Bits

The Atmel® ATtiny87/167 provides two lock bits which can be left unprogrammed (“1”) or can be programmed (“0”) to obtain

the additional features listed in Table 21-2. The lock bits can only be erased to “1” with the chip erase command. The

ATtiny87/167 has no separate boot loader section.

Table 21-1. Lock Bit Byte(1)

Lock Bit Byte Bit No Description Default Value

7 – 1 (unprogrammed)

6 – 1 (unprogrammed)

5 – 1 (unprogrammed)

4 – 1 (unprogrammed)

3 – 1 (unprogrammed)

2 – 1 (unprogrammed)

LB2 1Lock bit 1 (unprogrammed)

LB1 0Lock bit 1 (unprogrammed)

Note: “1” means unprogrammed, “0” means programmed.

Table 21-2. Lock Bit Protection Modes(1)(2)

Memory Lock Bits

Protection TypeLB Mode LB2 LB1

1 1 1 No memory lock features enabled.

2 1 0

Further programming of the flash and EEPROM is disabled in parallel and serial

Programming mode. The fuse bits are locked in both serial and parallel

Programming mode.(1)

3 0 0

Further programming and verification of the flash and EEPROM is disabled in

parallel and serial programming mode. The fuse bits are locked in both serial and

parallel programming mode.(1)

Notes: 1. Program the fuse bits before programming the LB1 and LB2.

2. “1” means unprogrammed, “0” means programmed

Notes: 1. Section 9.3.4 “Allemale Funchons of Perl B" on page 78 [or descriplion of RSTDISBL fuse. AtmeL

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21.2 Fuse Bits

The Atmel ATtiny87/167 has three fuse bytes. Table 21-3, Table 21-4 and Table 21-5 describe briefly the functionality of all

the fuses and how they are mapped into the fuse bytes.

The SPM instruction is enabled for the whole flash if the SELFPRGEN fuse is programmed (“0”), otherwise it is disabled.

Note that the fuses are read as logical zero, “0”, if they are programmed.

Table 21-3. Extended Fuse Byte

Fuse Extended Byte Bit No Description Default Value

– 7 – 1 (unprogrammed)

– 6 – 1 (unprogrammed)

– 5 – 1 (unprogrammed)

– 4 – 1 (unprogrammed)

– 3 – 1 (unprogrammed)

– 2 – 1 (unprogrammed)

– 1 – 1 (unprogrammed)

SELFPRGEN 0Self programming enable 1 (unprogrammed)

Table 21-4. Fuse High Byte

Fuse High Byte Bit No Description Default Value

RSTDISBL(1) 7External reset disable 1 (unprogrammed)

DWEN 6 DebugWIRE enable 1 (unprogrammed)

SPIEN(2) 5Enable serial program

and data downloading

0 (programmed,

SPI programming enabled)

WDTON(3) 4Watchdog timer always on 1 (unprogrammed)

EESAVE 3EEPROM memory is preserved

through the chip erase

1 (unprogrammed,

EEPROM not preserved)

BODLEVEL2(4) 2Brown-out detector trigger level 1 (unprogrammed)

BODLEVEL1(4) 1Brown-out detector trigger level 1 (unprogrammed)

BODLEVEL0(4) 0Brown-out detector trigger level 1 (unprogrammed)

Notes: 1. Section 9.3.4 “Alternate Functions of Port B” on page 78 for description of RSTDISBL fuse.

2. The SPIEN fuse is not accessible in serial programming mode.

3. Section 6.3.3 “Watchdog Timer Control Register - WDTCR” on page 55 for details.

4. See Table 22-5 on page 226 for BODLEVEL fuse coding.

Notes: 1. The default value of SUT1..0 results in maximum start-up time for the default clock source. See Tame 474 on AtmeL

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21.2.1 Latching of Fuses

The fuse values are latched when the device enters programming mode and changes of the fuse values will have no effect

until the part leaves programming mode. This does not apply to the EESAVE Fuse which will take effect once it is

programmed. The fuses are also latched on power-up in normal mode.

21.3 Signature Bytes

All Atmel® microcontrollers have a three-byte signature code which identifies the device. This code can be read in both serial

and parallel mode, also when the device is locked. The three bytes reside in a separate address space.

21.4 Calibration Byte

The Atmel ATtiny87/167 has a byte calibration value for the internal RC oscillator. This byte resides in the high byte of

address 0x000 in the signature address space. During reset, this byte is automatically written into the OSCCAL register to

ensure correct frequency of the calibrated RC oscillator.

Table 21-5. Fuse Low Byte

Fuse Low Byte Bit No Description Default Value

CKDIV8(4) 7Divide clock by 8 0 (programmed)

CKOUT(3) 6Clock output 1 (unprogrammed)

SUT1 5Select start-up time 1 (unprogrammed)(1)

SUT0 4Select start-up time 0 (programmed)(1)

CKSEL3 3Select Clock source 0 (programmed)(2)

CKSEL2 2Select Clock source 0 (programmed)(2)

CKSEL1 1Select Clock source 1 (unprogrammed)(2)

CKSEL0 0Select Clock source 0 (programmed)(2)

Notes: 1. The default value of SUT1..0 results in maximum start-up time for the default clock source. See Table 4-4 on

page 28 for details.

2. The default setting of CKSEL3..0 results in internal RC Oscillator @ 8 MHz. See Table 4-3 on page 28 for

details.

3. The CKOUT Fuse allows the system clock to be output on PORTB5. See Section 4.2.7 “Clock Output Buffer”

on page 32 for details.

4. See Section 4.4 “System Clock Prescaler” on page 38for details.

Table 21-6. Signature Bytes

Device Address Value Signature Byte Description

ATtiny87

00x1E Indicates manufactured by Atmel

10x93 Indicates 8KB flash memory

20x87 Indicates ATtiny87 device when address 1 contains 0x93

ATtiny167

00x1E Indicates manufactured by Atmel

10x94 Indicates 16KB flash memory

20x87 Indicates ATtiny167 device when address 1 contains 0x94

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21.5 Page Size

21.6 Parallel Programming Parameters, Pin Mapping, and Commands

This section describes how to parallel program and verify flash program memory, EEPROM Data memory, memory lock bits,

and fuse bits in the Atmel ATtiny87/167. Pulses are assumed to be at least 250 ns unless otherwise noted.

21.6.1 Signal Names

In this section, some pins of the Atmel® ATtiny87/167 are referenced by signal names describing their functionality during

parallel programming, see Figure 21-1 and Figure 21-9. Pins not described in the following table are referenced by pin

names.

The XA1/XA0 pins determine the action executed when the XTAL1 pin is given a positive pulse. The bit coding is shown in

Figure 21-11 on page 211.

When pulsing WR or OE, the command loaded determines the action executed. The different commands are shown in

Figure 21-12 on page 211.

Figure 21-1. Parallel programming

Note: Vcc - 0.3V < AVcc < Vcc + 0.3V, however, AVcc should always be within 4.5 - 5.5V

Table 21-7. Number of Words in a Page and No. of Pages in the Flash

Device Flash Size Page Size PCWORD No. of Pages PCPAGE PCMSB

ATtiny87 4K words 64 words PC[5:0] 64 PC[11:6] 11

ATtiny167 8K words 64 words PC[5:0] 128 PC[12:6] 12

Table 21-8. Number of Words in a Page and No. of Pages in the EEPROM

Device EEPROM Size Page Size PCWORD No. of Pages PCPAGE EEAMSB

ATtiny87

ATtiny167 512 bytes 4 bytes EEA[1:0] 128 EEA[8:2] 8

GND

PB0

PB1

PB2

PB3

XTAL1/ PB4

DATA

PB5

PB6

RESET/PB7

VCC

AVCC

PA7 to PA0

+4.5 to +5.5V

RDY/BSY

XA1/BS2

XA0

PAGEL/ BS1

+12V

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Table 21-9. Pin Name Mapping

Signal Name in

Programming Mode Pin Name I/O Function

WR PB0 I Write pulse (active low).

XA0 PB1 I XTAL1 action bit 0

XA1 / BS2 PB2 I

- XTAL1 action bit 1

- Byte select 2

(“0” selects low byte, “1” selects 2’nd high byte)

PAGEL / BS1 PB3 I

- Program memory and EEPROM data page load

- Byte select 1

(“0” selects low byte, “1” selects high byte)

PB4 I XTAL1 (clock input)

OE PB5 I Output enable (active low).

RDY / BSY PB6 O 0: Device is busy programming,

1: Device is ready for new command.

+12V PB7 I - Reset (active low)

- Parallel programming mode (+12V).

DATA PA7-PA0 I/O Bi-directional data bus (output when OE is low).

Table 21-10. Pin Values Used to Enter Programming Mode

Pin Symbol Value

PAGEL / BS1 Prog_enable[3] 0

XA1 / BS2 Prog_enable[2] 0

XA0 Prog_enable[1] 0

WR Prog_enable[0] 0

Table 21-11. XA1 and XA0 Coding

XA1 XA0 Action when XTAL1 is Pulsed

0 0 Load flash or EEPROM address (high or low address byte determined by BS1).

0 1 Load data (high or low data byte for flash determined by BS1).

1 0 Load command

1 1 No action, idle

Table 21-12. Command Byte Bit Coding

Command Byte Command Executed

1000 0000 bChip erase

0100 0000 bWrite fuse bits

0010 0000 bWrite lock bits

0001 0000 bWrite flash

0001 0001 bWrite EEPROM

0000 1000 bRead signature bytes and calibration byte

0000 0100 bRead fuse and lock bits

0000 0010 bRead flash

0000 0011 bRead EEPROM

Load Command “Write Flash" Load Address Low bﬁe AtmeL

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21.7 Parallel Programming

21.7.1 Enter Programming Mode

The following algorithm puts the device in parallel programming mode:

1. Apply 4.5 - 5.5V between Vcc and GND.

2. Set RESET to “0” and toggle XTAL1 at least six times.

3. Set the prog_enable pins listed in Table 21-10 to “0000 b” and wait at least 100ns.

4. Apply 11.5 - 12.5V to RESET. Any activity on Prog_enable pins within 100ns after +12V has been applied to

RESET, will cause the device to fail entering programming mode.

5. Wait at least 50µs before sending a new command.

21.7.2 Considerations for Efficient Programming

The loaded command and address are retained in the device during programming. For efficient programming, the following

should be considered.

●The command needs only be loaded once when writing or reading multiple memory locations.

●Skip writing the data value 0xFF, that is the contents of the entire EEPROM (unless the EESAVE fuse is programmed)

and flash after a chip erase.

●Address high byte needs only be loaded before programming or reading a new 256 word window in flash or 256 byte

EEPROM. This consideration also applies to signature bytes reading.

21.7.3 Chip Erase

The chip erase will erase the flash and EEPROM(1) memories plus lock bits. The lock bits are not reset until the program

memory has been completely erased. The fuse bits are not changed. A chip erase must be performed before the flash

and/or EEPROM are reprogrammed.

Note: 1. The EEPRPOM memory is preserved during chip erase if the EESAVE fuse is programmed.

Load Command “chip erase”

1. Set XA1, XA0 to “1,0 ”. This enables command loading.

2. Set BS1 to “0”.

3. Set DATA to “1000 0000 b”. This is the command for chip erase.

4. Give XTAL1 a positive pulse. This loads the command.

5. Give WR a negative pulse. This starts the chip erase. RDY/BSY goes low.

6. Wait until RDY/BSY goes high before loading a new command.

21.7.4 Programming the Flash

The flash is organized in pages, see Table 21-7 on page 210. When programming the flash, the program data is latched into

a page buffer. This allows one page of program data to be programmed simultaneously. The following procedure describes

how to program the entire flash memory:

A. Load Command “Write Flash”

1. Set XA1, XA0 to “1,0”. This enables command loading.

2. Set BS1 to “0”.

3. Set DATA to “0001 0000 b”. This is the command for write flash.

4. Give XTAL1 a positive pulse. This loads the command.

B. Load Address Low byte

1. Set XA1, XA0 to “00”. This enables address loading.

2. Set BS1 to “0”. This selects low address.

3. Set DATA = address low byte (0x00 - 0xFF).

4. Give XTAL1 a positive pulse. This loads the address low byte.

Load Data Low Bﬁe Load Data High Bﬁe Latch Data Repeat B through E Load Address High bﬁe Program Page Repeat B through H End Page Programming AtmeL

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C. Load Data Low Byte

1. Set XA1, XA0 to “0,1”. This enables data loading.

2. Set DATA = data low byte (0x00 - 0xFF).

3. Give XTAL1 a positive pulse. This loads the data byte.

D. Load Data High Byte

1. Set BS1 to “1”. This selects high data byte.

2. Set XA1, XA0 to “0,1”. This enables data loading.

3. Set DATA = data high byte (0x00 - 0xFF).

4. Give XTAL1 a positive pulse. This loads the data byte.

E. Latch Data

1. Set BS1 to “1”. This selects high data byte.

2. Give PAGEL a positive pulse. This latches the data bytes. (See Figure 21-3 on page 214 for signal waveforms)

F. Repeat B through E until the entire buffer is filled or until all data within the page is loaded.

While the lower bits in the address are mapped to words within the page, the higher bits address the pages within the

FLASH. This is illustrated in Figure 21-2. Note that if less than eight bits are required to address words in the page

(pagesize < 256), the most significant bit(s) in the address low byte are used to address the page when performing a page

write.

G. Load Address High byte

1. Set XA1, XA0 to “0,0”. This enables address loading.

2. Set BS1 to “1”. This selects high address.

3. Set DATA = address high byte (0x00 - 0xFF).

4. Give XTAL1 a positive pulse. This loads the address high byte.

H. Program Page

1. Give WR a negative pulse. This starts programming of the entire page of data. RDY/BSY goes low.

2. Wait until RDY/BSY goes high (See Figure 21-3 on page 214 for signal waveforms).

I. Repeat B through H until the entire flash is programmed or until all data has been programmed.

J. End Page Programming

1. 1. Set XA1, XA0 to “1,0”. This enables command loading.

2. Set DATA to “0000 0000 b”. This is the command for no operation.

3. Give XTAL1 a positive pulse. This loads the command, and the internal write signals are reset.

Figure 21-2. Addressing the Flash Which is Organized in Pages

PAGEMSBPCMSB

WORD ADDRESS

WITHIN A PAGE

PAGE ADDRESS

WITHIN THE FLASH

PCWORDPCPAGE

PAGE INSTRUCTION WORD

PROGRAM MEMORY PAGE

PROGRAM COUNTER

PAGEEND

PCWORD [PAGEMSB:0]

Load command W W Load data M W W /—/% :XXXXXXXX —/—\_/—\— /_\/_\/_\/_\ /_\/_\ AtmeL

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Figure 21-3. Programming the Flash Waveforms (1)

Note: 1. “XX” is don’t care. The letters refer to the programming description above.

21.7.5 Programming the EEPROM

The EEPROM is organized in pages, see Table 21-8 on page 210. When programming the EEPROM, the program data is

latched into a page buffer. This allows one page of data to be programmed simultaneously. The programming algorithm for

the EEPROM data memory is as follows (refer to Section 21.7.4 “Programming the Flash” on page 212 for details on

command, address and data loading):

A: Load command “0001 0001 b”.

G: Load address high byte (0x00 - 0xFF).

B: Load address low byte (0x00 - 0xFF).

C: Load data (0x00 - 0xFF).

E: Latch data (give PAGEL a positive pulse).

K: Repeat A through E until the entire buffer is filled.

L: Program EEPROM page

1. Set BS1 to “0”.

2. Give WR a negative pulse. This starts programming of the EEPROM page. RDY/BSY goes low.

3. Wait until to RDY/BSY goes high before programming the next page (See Figure 21-4 for signal waveforms).

Figure 21-4. Programming the EEPROM Waveforms

XTAL1

RDY/ BSY

RESET +12V

PAGEL/BS1

XA0

XA1/BS2

DATA

ABCDEBCD

EGH

0x10 XXXXXX ADDR. HIGHADDR. LOWADDR. LOW DATA HIGHDATA HIGH DATA LOWDATA LOW

XTAL1

RDY/BSY

RESET +12V

PAGEL/BS1

XA0

XA1/BS2

DATA

ABCEBC

ADDR. HIGH ADDR. LOW0x11 DATA XX ADDR. LOW DATA XX

Load command Load address gh Load address low Load command Load address h gh Load address low Load command Load data low Load command Load data low Load command Load data low AtmeL

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21.7.6 Reading the Flash

The algorithm for reading the flash memory is as follows (refer to Section 21.7.4 “Programming the Flash” on page 212 for

details on command and address loading):

1. A: Load command “0000 0010 b”.

2. G: Load address high byte (0x00 - 0xFF).

3. B: Load address low byte (0x00 - 0xFF).

4. Set OE to “0”, and BS1 to “0”. The flash word low byte can now be read at DATA.

5. Set BS1 to “1”. The flash word high byte can now be read at DATA.

6. Set OE to “1”.

21.7.7 Reading the EEPROM

The algorithm for reading the EEPROM memory is as follows (refer to Section 21.7.4 “Programming the Flash” on page 212

for details on command and address loading):

1. A: Load command “0000 0011 b”.

2. G: Load address high byte (0x00 - 0xFF).

3. B: Load address low byte (0x00 - 0xFF).

4. Set OE to “0”, and BS1 to “0”. The EEPROM data byte can now be read at DATA.

5. Set OE to “1”.

21.7.8 Programming the Fuse Low Bits

The algorithm for programming the fuse low bits is as follows (refer to Section 21.7.4 “Programming the Flash” on page 212

for details on command and data loading):

1. A: Load command “0100 0000 b”.

2. C: Load data low byte. Bit n = “0” programs and bit n = “1” erases the fuse bit.

3. Give WR a negative pulse and wait for RDY/BSY to go high.

21.7.9 Programming the Fuse High Bits

The algorithm for programming the fuse high bits is as follows (refer to Section 21.7.4 “Programming the Flash” on page 212

for details on command and data loading):

1. A: Load command “0100 0000 b”.

2. C: Load data low byte. Bit n = “0” programs and bit n = “1” erases the fuse bit.

3. Set BS1 to “1” and BS2 to “0”. This selects high data byte.

4. Give WR a negative pulse and wait for RDY/BSY to go high.

5. Set BS1 to “0”. This selects low data byte.

21.7.10 Programming the Extended Fuse Bits

The algorithm for programming the extended fuse bits is as follows (refer to Section 21.7.4 “Programming the Flash” on page

212 for details on command and data loading):

1. A: Load command “0100 0000 b”.

2. C: Load data low byte. Bit n = “0” programs and bit n = “1” erases the fuse bit.

3. Set BS1 to “0” and BS2 to “1”. This selects extended data byte.

4. Give WR a negative pulse and wait for RDY/BSY to go high.

5. Set BS2 to “0”. This selects low data byte.

Load command Load data low Load command AtmeL

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Figure 21-5. Programming the FUSES Waveforms

21.7.11 Programming the Lock Bits

The algorithm for programming the lock bits is as follows (refer to Section 21.7.4 “Programming the Flash” on page 212 for

details on command and data loading):

1. A: Load command “0010 0000 b”.

2. C: Load data low byte. Bit n = “0” programs the lock bit. If LB mode 3 is programmed (LB1 and LB2 is pro-

grammed), it is not possible to re-program the lock bits by any external programming mode.

3. Give WR a negative pulse and wait for RDY/BSY to go high.

4. The lock bits can only be cleared by executing chip erase.

21.7.12 Reading the Fuse and Lock Bits

The algorithm for reading the fuse and lock bits is as follows (refer to Section 21.7.4 “Programming the Flash” on page 212

for details on command loading):

1. A: Load command “0000 0100 b”.

2. Set OE to “0”, BS2 to “0” and BS1 to “0”. The status of the fuse low bits can now be read at DATA (“0” means

programmed).

3. Set OE to “0”, BS2 to “1” and BS1 to “1”. The status of the fuse high bits can now be read at DATA (“0” means

programmed).

4. Set OE to “0”, BS2 to “1”, and BS1 to “0”. The status of the extended fuse bits can now be read at DATA (“0”

means programmed).

5. Set OE to “0”, BS2 to “0” and BS1 to “1”. The status of the lock bits can now be read at DATA (“0” means

programmed).

6. Set OE to “1”.

XTAL1

RDY/BSY

RESET +12V

PAGEL/BS1

XA0

XA1/BS2

DATA

0x40 DAT A XX

DATA DATAXX XX

0x400x40

Write Fuse Low Byte Write fuse High Byte Write Extended Fuse Byte

Load command Load address low Load command Load address low Load command AtmeL

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Figure 21-6. Mapping Between BS1, BS2 and the Fuse and Lock Bits During Read

21.7.13 Reading the Signature Bytes

The algorithm for reading the signature bytes is as follows (refer to Section 21.7.4 “Programming the Flash” on page 212 for

details on command and address loading):

1. A: Load command “0000 1000 b”.

2. B: Load address low byte (0x00 - 0x02).

3. Set OE to “0”, and BS to “0”. The selected signature byte can now be read at DATA.

4. Set OE to “1”.

21.7.14 Reading the 8MHz RC Oscillator Calibration Byte

The algorithm for reading the 8MHz RC oscillator calibration byte is as follows (refer to Section 21.7.4 “Programming the

Flash” on page 212 for details on command and address loading):

1. A: Load command “0000 1000 b”.

2. B: Load address low byte, 0x00.

3. Set OE to “0”, and BS1 to “1”. The 8MHz RC oscillator calibration byte can now be read at DATA.

4. Set OE to “1”.

21.7.15 Reading the Temperature Sensor Parameter Bytes

The algorithm for reading the temperature sensor parameter bytes is as follows (refer to Section 21.7.4 “Programming the

Flash” on page 212 for details on command and address loading):

1. A: Load command “0000 1000 b”.

2. B: Load address ow byte, 0x0003 or 0x0005.

3. Set OE to “0”, and BS1 to “1”. The temperature sensor parameter byte can now be read at DATA.

4. Set OE to “1”.

Fuse Low Byte

Extended Fuse Byte

BS2

Lock Bits

Fuse High Byte

BS2

BS1

DATA

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21.8 Serial Downloading

Both the flash and EEPROM memory arrays can be programmed using the serial SPI bus while RESET is pulled to GND.

The serial interface consists of pins SCK, MOSI (input) and MISO (output). After RESET is set low, the programming enable

instruction needs to be executed first before program/erase operations can be executed.

Note: In Table 21-13 on page 218, the pin mapping for SPI programming is listed. Not all parts use the SPI pins ded-

icated for the internal SPI interface.

Figure 21-7. Serial Programming and Verify (1)

Note: 1. If the device is clocked by the internal oscillator, it is no need to connect a clock source to the XTAL1 pin

When programming the EEPROM, an auto-erase cycle is built into the self-timed programming operation (in the serial mode

ONLY) and there is no need to first execute the chip erase instruction. The chip erase operation turns the content of every

memory location in both the program and EEPROM arrays into 0xFF.

Depending on CKSEL fuses, a valid clock must be present. The minimum low and high periods for the serial clock (SCK)

input are defined as follows:

Low:> 2 CPU clock cycles for fck < 12MHz, 3 CPU clock cycles for fck ≥ 12Hz

High:> 2 CPU clock cycles for fck < 12MHz, 3 CPU clock cycles for fck ≥ 12MHz

21.8.1 Serial Programming Algorithm

When writing serial data to the Atmel® ATtiny87/167, data is clocked on the rising edge of SCK.

When reading data from the ATtiny87/167, data is clocked on the falling edge of SCK. See Figure 21-7 and Figure 21-8 on

page 221 for timing details.

To program and verify the Atmel ATtiny87/167 in the serial programming mode, the following sequence is recommended

(see four byte instruction formats in Table 21-15 on page 220):

1. Power-up sequence: Apply power between Vcc and GND while RESET and SCK are set to “0”. In some systems,

the programmer can not guarantee that SCK is held low during power-up. In this case, RESET must be given a

positive pulse of at least two CPU clock cycles duration after SCK has been set to “0”.

2. Wait for at least 20ms and enable serial programming by sending the programming enable serial instruction to pin

MOSI.

Table 21-13. Pin Mapping Serial Programming

Symbol Pin Name I/O Function

MOSI PA4 ISerial data in

MISO PA2 OSerial data out

SCK PA5 ISerial clock

GND

PA5

PA2

RESET/PB7

VCC

MOSI

MISO

SCK

+2.7 to +5.5V

PA4

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3. The serial programming instructions will not work if the communication is out of synchronization. When in sync.

the second byte (0x53), will echo back when issuing the third byte of the programming enable instruction. Whether

the echo is correct or not, all four bytes of the instruction must be transmitted. If the 0x53 did not echo back, give

RESET a positive pulse and issue a new programming enable command.

4. The flash is programmed one page at a time. The memory page is loaded one byte at a time by supplying the 5

LSB of the address and data together with the load program memory page instruction. To ensure correct loading

of the page, the data low byte must be loaded before data high byte is applied for a given address. The program

memory page is stored by loading the write program memory age instruction with the 6 MSB of the address. If

polling (RDY/BSY) is not used, the user must wait at least t WD_FLASH before issuing the next page.

(See Table 21-14) accessing the serial programming interface before the flash write operation completes can

result in incorrect programming.

5. A: The EEPROM array is programmed one byte at a time by supplying the address and data together with the

appropriate write instruction. An EEPROM memory location is first automatically erased before new data is writ-

ten. If polling (RDY/BSY) is not used, the user must wait at least t WD_EEPROM before issuing the next byte.

(See Table 21-14) in a chip erased device, no 0xFFs in the data file(s) need to be programmed.

B: The EEPROM array is programmed one page at a time. The memory page is loaded one byte at a time by sup-

plying the 2 LSB of the address and data together with the load EEPROM memory page instruction. The

EEPROM memory page is stored by loading the write EEPROM memory page instruction with the 6 MSB of the

address. When using EEPROM page access only byte locations loaded with the Load EEPROM memory page

instruction is altered. The remaining locations remain unchanged. If polling (RDY/BSY) is not used, the used must

wait at least t WD_EEPROM before issuing the next page (See Table 21-8 on page 210). In a chip erased device, no

0xFF in the data file(s) need to be programmed.

6. Any memory location can be verified by using the read instruction which returns the content at the selected

address at serial output MISO.

7. At the end of the programming session, RESET can be set high to commence normal operation.

8. Power-off sequence (if needed):

Set RESET to “1”.

Turn Vcc power off.

Table 21-14. Minimum Wait Delay Before Writing the Next Flash or EEPROM Location

Symbol Minimum Wait Delay

t WD_FLASH 4.5ms

t WD_EEPROM 4.0ms

t WD_ERASE 4.0ms

t WD_FUSE 4.5ms

Notes: 1. Notall instructions are applicable forall pans.

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21.8.2 Serial Programming Instruction set

Table 21-15 and Figure 21-8 on page 221 describes the instruction set

Table 21-15. Serial Programming Instruction Set

Instruction/Operation

Instruction Format

Byte 1 Byte 2 Byte 3 Byte4

Programming enable 0xAC 0x53 0x00 0x00

Chip erase (program memory/EEPROM) 0xAC 0x80 0x00 0x00

Poll RDY/BSY 0xF0 0x00 0x00 data byte out

Load Instructions

Load extended address byte(1) 0x4D 0x00 Extended add. 0x00

Load program memory page, high byte 0x48 add. MSB add. LSB high data byte in

Load program memory page, low byte 0x40 add. MSB add. LSB low data byte in

Load EEPROM memory page (page

access) 0xC1 0x00 0000 000aa b data byte in

Read Instructions

Read program memory, high byte 0x28 add. MSB add. LSB high data byte out

Read program memory, low byte 0x20 add. MSB add. LSB low data byte out

Read EEPROM memory 0xA0 0x00 00aa aaaa data byte out

Read lock bits 0x58 0x00 0x00 data byte out

Read signature byte 0x30 0x00 0000 000aa data byte out

Read fuse bits 0x50 0x00 0x00 data byte out

Read fuse high bits 0x58 0x08 0x00 data byte out

Read extended fuse bits 0x50 0x08 0x00 data byte out

Read calibration byte 0x38 0x00 0x00 data byte out

Write Instructions(6)

Write program memory page 0x4C add. MSB add. LSB 0x00

Write EEPROM memory 0xC0 0x00 00aa aaaa b data byte in

Write EEPROM memory page (page

access) 0xC2 0x00 00aa aa00 b 0x00

Write lock bits 0xAC 0xE0 0x00 data byte in

Write fuse bits 0xAC 0xA0 0x00 data byte in

Write fuse high bits 0xAC 0xA8 0x00 data byte in

Write extended fuse bits 0xAC 0xA4 0x00 data byte in

Notes: 1. Not all instructions are applicable for all parts.

2. a = address

3. Bits are programmed ‘0’, unprogrammed ‘1’.

4. To ensure future compatibility, unused fuses and lock bits should be unprogrammed (‘1’).

5. Refer to the corresponding section for fuse and lock bits, calibration and signature bytes and page size.

6. Instructions accessing program memory use a word address. This address may be random within the page

range.

7. See http://www.atmel.com/avr for application notes regarding programming and programmers.

U /1:XXXXXXX\ Hl'll'll'll'll'll'll'l ¢¢¢¢¢¢¢¢ AtmeL

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If the LSB in RDY/BSY data byte out is ‘1’, a programming operation is still pending. Wait until this bit returns ‘0’ before the

next instruction is carried out.

Within the same page, the low data byte must be loaded prior to the high data byte.

After data is loaded to the page buffer, program the EEPROM page, see Figure 21-8.

Figure 21-8. Serial programming Instruction Example

21.9 Serial Programming Characteristics

Figure 21-9. Serial Programming Waveforms

For characteristics of the SPI module, see Section 22.10 “SPI Timing Characteristics” on page 231

Addr. MSB

Bit 15 B Bit 15 B 00

Load Program Memory Page (High/Low Byte)

Load EEPROM Memory Page (page access)

Write Program Memory Page/

Write EEPROM Memory Page

Byte 1 Byte 2 Byte 3 Byte 4

Page 0

Page 1

Page 2

Page N-1

Byte 1 Byte 2 Byte 3 Byte 4

Addr. LSB

Page Offset

Page Number

Addr. MSB Addr. LSB

Page Buffer

Serial Programming Instruction

Program Memory/

EEPROM Memory

MSB

SERIAL DATA INPUT

(MOSI)

SERIAL DATA OUTPUT

(MISO) MSB

LSB

SERIAL CLOCK INPUT

(SCK)

SAMPLE

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22. Electrical Characteristics

Note: All Characteristics contained in this data sheet are based on simulation and characterization of Atmel®

ATtiny87/167 AVR® microcontrollers manufactured in a typical process technology. These values are prelimi-

nary values representing design targets, and will be updated after characterization of actual Automotive silicon.

22.1 Absolute Maximum Ratings

Stresses beyond those listed under “absolute maximum ratings” may cause permanent damage to the device. This is a stress rating

only and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of this

specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.

Parameters Symbol Min. Max. Unit

Operating temperature –40 +125 °C

Storage temperature –65 +150 °C

Voltage on any pin except RESET

with respect to ground –0.5 Vcc+0.5 V

Voltage on RESET with respect to ground –0.5 +13.0 V

Voltage on Vcc with respect to ground –0.5 6.0 V

DC current per I/O Pin

DC current Vcc and GND Pins

Injection current at VCC = 0V to 5V(2) –5(1)

40.0

200.0

+5(1)

Notes: 1. Maximum current per port = ±30mA

2. Functional corruption may occur.

22.2 DC Characteristics

TA = -40°C to +125°C, Vcc = 2.7V to 5.5V (unless otherwise noted)

Parameter Condition Symbol Min. Typ.(1) Max. Units

Input low voltage

Except XTAL1 and RESET

pins VIL –0.5 0.2 Vcc(2) V

XTAL1 pin - external clock

selected VIL1 –0.5 0.1 Vcc(2) V

RESET pin VIL2 –0.5 0.2 Vcc(2) V

RESET pin as I/O VIL3 – 0.5 0.2 Vcc(2) V

Input high voltage

Except XTAL1 and RESET

pins VIH 0.7 Vcc(3) Vcc + 0.5 V

XTAL1 pin - external clock

selected VIH1 0.8 Vcc(3) Vcc + 0.5 V

RESET pin VIH2 0.9 Vcc(3) Vcc + 0.5 V

RESET pin as I/O VIH3 0.7 Vcc(3) Vcc + 0.5 V

Output low loltage (4)

(Ports A, B,)

IOL = 10mA, Vcc = 5V

IOL = 5 A, Vcc = 3V VOL

0.6

0.5 V

Output high voltage(5)

(Ports A, B)

IOH = – 10mA, Vcc = 5V

IOH = – 5mA, Vcc = 3V VOH

4.3

2.5 V

Input leakage

Current I/O pin

Vcc = 5.5V, pin low

(absolute value) IIL < 0.05 1µA

Input leakage

Current I/O pin

Vcc = 5.5V, pin high

(absolute value) IIH < 0.05 1µA

Reset pull-up resistor RRST 30 60 k

I/O pin pull-up resistor Rpu 20 50 k

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Notes: 1. “Typ.”, typical values at 25°C. Maximum values are characterized values and not test limits in production.

2. “Max.” means the highest value where the pin is guaranteed to be read as low.

3. “Min.” means the lowest value where the pin is guaranteed to be read as high.

4. Although each I/O port can sink more than the test conditions (10mA at Vcc= 5V, 5mA at Vcc = 3V) under steady state

conditions (non-transient), the following must be observed: The sum of all IOL, for all ports, should not exceed 120mA.

If IOL exceeds the test condition, VOL may exceed the related specification. Pins are not guaranteed to sink current

greater than the listed test condition.

5. Although each I/O port can source more than the test conditions (10mA at Vcc = 5V, 5mA at Vcc = 3V) under steady state

conditions (non-transient), the following must be observed: The sum of all IOH, for all ports, should not exceed 120mA.

If IOH exceeds the test condition, VOH may exceed the related specification. Pins are not guaranteed to source current

greater than the listed test condition.

6. Values using methods described in Section 5.8 “Minimizing Power Consumption” on page 44. Power reduction is

enabled (PRR = 0xFF) and there is no I/O drive.

7. BOD disabled.

Power supply current(6)

Active mode

(external clock)

16MHz, Vcc = 5V

ICC

10 13 mA

8MHz, Vcc = 5V 5.5 7.0 mA

8MHz, Vcc = 3V 2.8 3.5 mA

4MHz, Vcc = 3V 1.8 2.5 mA

Power supply current(6)

Idle mode

(external clock)

16MHz, Vcc = 5V 3.5 5.0 mA

8MHz, Vcc = 5V 1.8 2.5 mA

8MHz, Vcc = 3V 11.5 mA

4MHz, Vcc = 3V 0.5 0.8 mA

Power supply current(7)

Power-down mode

WDT enabled, Vcc = 5V 7100 µA

WDT disabled, Vcc = 5V 0.18 70 µA

WDT enabled, Vcc = 3V 570 µA

WDT disabled, Vcc = 3V 0.15 45 µA

Analog comparator

Input offset voltage

Vcc = 5V

Vin = Vcc/2 VACIO -10 10 40 mV

Analog comparator

Input leakage current

Vcc = 5V

Vin = Vcc/2 IACLK -50 50 nA

Analog comparator

Propagation delay

Common mode Vcc/2

Vcc = 2.7V

tACID

170 ns

Vcc = 5.0V 180 ns

22.2 DC Characteristics (Continued)

TA = -40°C to +125°C, Vcc = 2.7V to 5.5V (unless otherwise noted)

Parameter Condition Symbol Min. Typ.(1) Max. Units

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22.3 Speed Grades

Figure 22-1. Maximum Frequency versus Vcc, ATtiny87/167

22.4 Clock Characteristics

22.4.1 Calibrated Internal RC Oscillator Accuracy

22.4.2 External Clock Drive Waveforms

Figure 22-2. External Clock Drive Waveforms

16MHz

2.7V 4.5V

Safe Operating Area

5.5V

8MHz

Frequency

Voltage

Table 22-1. Calibration and Accuracy of Internal RC Oscillator

Frequency Vcc Temperature Accuracy

Factory

calibration 8.0MHz 3V 25°C ±2%

Maximum

deviation 8.0MHz 2.7V –40°C/+125°C ±10%

5.5V –40°C/+125°C ±10%

tCHCX

VIH1

VIL1

tCHCX

tCLCH tCHCL

tCLCX

tCLCL

Note: 1. Before rising, the supply has to be between VPORMIN and VPORMAX to ensure a reset. AtmeL

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22.4.3 External Clock Drive

22.5 RESET Characteristics

Table 22-2. External Clock Drive

Parameter Symbol

Vcc = 2.7 - 5.5V Vcc = 4.5 - 5.5V

UnitsMin. Max. Min. Max.

Oscillator frequency 1/tCLCL 0 8 0 16 MHz

Clock period tCLCL 125 62.5 ns

High time tCHCX 50 25 ns

Low time tCLCX 50 25 ns

Rise time tCLCH 1.6 0.5 ms

Fall time tCHCL 1.6 0.5 ms

Change in period from one clock cycle to the

next tCLCL 2 2 %

Table 22-3. External Reset Characteristics

Parameter Condition Symbol Min Typ Max Units

RESET pin threshold voltage VCC = 5V VRST 0.1 Vcc 0.9 Vcc V

Minimum pulse width on RESET pin VCC = 5V tRST 2.5 µs

Bandgap reference voltage VCC = 2.7V, TA= 25°C VBG 1.0 1.1 1.2 V

Bandgap reference start-up time VCC = 2.7V, TA= 25°C tBG 40 70 µs

Bandgap reference current

consumption VCC = 2.7V, TA= 25°C IBG 15 µA

Table 22-4. Power On Reset Characteristics

Parameter Symbol Min Typ Max Units

Power-on reset threshold voltage (rising) VPOT 1.4 V

Power-on reset threshold voltage (falling)(1) 1.0 1.3 1.6 V

VCC max. start voltage to ensure internal power-on

reset signal VPORMAX 0.4 V

VCC Min. start voltage to ensure internal power-on reset

signal VPORMIN –0.1 V

VCC rise rate to ensure power-on reset VCCRR 0.01 V/ms

RESET pin threshold voltage VRST 0.1 Vcc 0.9 Vcc V

Note: 1. Before rising, the supply has to be between VPORMIN and VPORMAX to ensure a reset.

Notes: 1. V may be below nominal minimum operating voltage for some devices. For devices where this is the case, — — AtmeL

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22.6 Internal Voltage Characteristics

22.7 Current Source Characteristics

Table 22-5. BODLEVEL Fuse Coding

BODLEVEL 2:0 Fuses Min. VBOT

(1) Typ. VBOT Max. VBOT Units

1 1 1 b BOD Disabled

1 1 0 b 1.7 1.8 2.0

1 0 1 b 2.5 2.7 2.9

1 0 0 b 4.1 4.3 4.5

0 1 1 b

Reserved

0 1 0 b

0 0 1 b

0 0 0 b

Notes: 1. VBOT may be below nominal minimum operating voltage for some devices. For devices where this is the case,

the device is tested down to Vcc = VBOT during the production test. This guarantees that a brown-out reset will

occur before Vcc drops to a voltage where correct operation of the microcontroller is no longer guaranteed.

The test is performed using BODLEVEL = 101 for low operating voltage and BODLEVEL = 100 for high oper-

ating voltage.

Table 22-6. Brown-out Characteristics

Parameter Symbol Min. Typ. Max. Units

Brown-out detector hysteresis VHYST 80 mV

Min pulse width on brown-out reset tBOD 2µs

Table 22-7. Internal Voltage Reference Characteristics

Parameter Condition Symbol Min. Typ. Max. Units

Bandgap reference voltage Vcc = 4.5

TA= 25°C VBG 1.0 1.1 1.2 V

Bandgap reference start-up time Vcc = 4.5

TA= 25°C tBG 40 70 µs

Bandgap reference current consumption Vcc = 4.5

TA= 25°C IBG 10 µA

Table 22-8. Current Source Characteristics

Parameter Condition Symbol Min. Typ. Max. Units

Current Vcc = 2.7 V/5.5 V

T = –40°C/+125°C IISRC 94 106 µA

Current Source start-up time Vcc = 4.5

TA=25°C tISRC 60 µs

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22.8 ADC Characteristics

Table 22-9. ADC Characteristics, Single Ended Channels (–40°C/+125°C)

Parameter Condition Symbol Min Typ Max Units

Resolution Single ended conversion 10 Bits

Absolute accuracy Vcc = 4V, VRef = 4V,

ADC clock = 200kHz TUE 2.0 3.5 LSB

Integral non linearity Vcc = 4V, VRef = 4V,

ADC clock = 200kHz INL 0.6 2.0 LSB

Differential non linearity Vcc = 4V, VRef = 4V,

ADC clock = 200kHz DNL 0.3 0.8 LSB

Gain error Vcc = 4V, VRef = 4V,

ADC clock = 200kHz -6.0 -2.5 2.0 LSB

Offset error Vcc = 4V, VRef = 4V,

ADC clock = 200kHz -3.5 1.5 3.5 LSB

Ref voltage VREF 2.56 AVcc V

Input bandwidth 38.5 kHz

Internal voltage VINT 2.4 2.56 2.7 V

Reference input resistance RREF 32 k

Analog input resistance RAIN 100 M

Table 22-10. ADC Characteristics, Differential Channels (–40°C/+125°C)

Parameter Condition Symbol Min Typ Max Units

Resolution Differential conversion 8

Absolute accuracy

Gain = 8x, BIPOLAR

VREF = 4V, Vcc = 5V

ADC clock = 200kHz

TUE

1.0 3.0

LSB

Gain = 20x, BIPOLAR

VREF = 4V, Vcc = 5V

ADC clock = 200kHz

1.5 3.5

Gain = 8x, UNIPOLAR

VREF = 4V, Vcc = 5V

ADC clock = 200kHz

2.0 4.5

Gain = 20x, UNIPOLAR

VREF = 4V, Vcc = 5V

ADC clock = 200kHz

2.0 6.0

Integral non linearity

Gain = 8x, BIPOLAR

VREF = 4V, Vcc = 5V

ADC clock = 200kHz

INL

0.2 1.0

LSB

Gain = 20x, BIPOLAR

VREF = 4V, Vcc = 5V

ADC clock = 200kHz

0.4 1.5

Gain = 8x, UNIPOLAR

VREF = 4V, Vcc = 5V

ADC clock = 200kHz

0.5 2.0

Gain = 20x, UNIPOLAR

VREF = 4V, Vcc = 5V

ADC clock = 200kHz

1.6 5.0

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Differential non linearity

Gain = 8x, BIPOLAR

VREF = 4V, Vcc = 5V

ADC clock = 200kHz

DNL

0.3 0.8

LSB

Gain = 20x, BIPOLAR

VREF = 4V, Vcc = 5V

ADC clock = 200kHz

0.3 0.8

Gain = 8x, UNIPOLAR

VREF = 4V, Vcc = 5V

ADC clock = 200kHz

0.4 0.8

Gain = 20x, UNIPOLAR

VREF = 4V, Vcc = 5V

ADC clock = 200kHz

0.6 1.6

Gain error

Gain = 8x, BIPOLAR

VREF = 4V, Vcc = 5V

ADC clock = 200kHz

-3.0 1.0 3.0

LSB

Gain = 20x, BIPOLAR

VREF = 4V, Vcc = 5V

ADC clock = 200kHz

–4.0 1.5 4.0

Gain = 8x, UNIPOLAR

VREF = 4V, Vcc = 5V

ADC clock = 200kHz

–5.0 –2.5 0.0

Gain = 20x, UNIPOLAR

VREF = 4V, Vcc = 5V

ADC clock = 200kHz

–4.0 –0.5 4.0

Offset error

Gain = 8x or 20x, BIPOLAR

VREF = 4V, Vcc = 5V

ADC clock = 200kHz

–2.0 0.5 2.0

LSB

Gain = 8x or 20x,

UNIPOLAR

VREF = 4V, Vcc = 5V

ADC clock = 200kHz

–2.0 0.5 2.0

Reference voltage VREF 2.56 AVCC - 0.5 V

Input differential voltage VDIFF –VREF/Gain +VREF/Gain V

Analog supply voltage AVcc Vcc – 0.3 Vcc + 0.3 V

Input voltage Differential conversion VIN 0AVcc V

ADC conversion output –511 +511 LSB

Input bandwidth Differential conversion 4kHz

Internal voltage reference VINT 2.4 2.56 2.7 V

Reference input resistance RREF 32 k

Analog input resistance RAIN 100 M

Table 22-10. ADC Characteristics, Differential Channels (–40°C/+125°C) (Continued)

Parameter Condition Symbol Min Typ Max Units

AtmeL

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22.9 Parallel Programming Characteristics

Figure 22-3. Parallel Programming Timing, Including some General Timing Requirements

Figure 22-4. Parallel Programming Timing, Loading Sequence with Timing Requirements(1)

Note: 1. The timing requirements shown in Figure 22-3 on page 229 (i.e., tDVXH, tXHXL, and tXLDX) also apply to loading

operation.

XTAL1

RDY/ BSY

Data and Control

(DATA, XAO,

XA1/BS2,

PAGEL/BS1)

tXHXL

tXLWL

tDVXH

tBVPH tPLBX tBVWL tWLBX

tPLWL

tWLWH

tRLRH

tWLRH

tXLDX

XTAL1

PAGEL/BS1

DATA

XA0

XA1/BS2

tXLXH

Load Address

(Low Byte)

Load Data

(Low Byte)

Load Data

(High Byte)

Load Address

(Low Byte)

ADDR0 (Low Byte) ADDR1 (Low Byte)DATA (Low Byte) DATA (High Byte)

Notes: 1. t is valid for ihe Write Flash, Wriie EEPROM. Wnle Fuse bits and Wriie Lock bus commands. AtmeL

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230

Figure 22-5. Parallel Programming Timing, Reading Sequence (within the Same Page) with Timing Requirements(1)

Note: 1. The timing requirements shown in Figure 22-3 on page 229 (i.e., tDVXH, tXHXL, and tXLDX) also apply to reading

operation.

Table 22-11. Parallel Programming Characteristics, VCC = 5V ± 10%

Parameter Symbol Min Typ Max Units

Programming enable voltage VPP 11.5 12.5 V

Programming enable current IPP 250 µA

Data and control valid before XTAL1 high tDVXH 67 ns

XTAL1 low to XTAL1 high tXLXH 200 ns

XTAL1 pulse width high tXHXL 150 ns

Data and control hold after XTAL1 low tXLDX 67 ns

XTAL1 low to WR low tXLWL 0ns

BS1 valid before PAGEL high tBVPH 67 ns

BS1 hold after PAGEL low tPLBX 67 ns

BS2/1 hold after WR low tWLBX 67 ns

PAGEL low to WR low tPLWL 67 ns

BS1 valid to WR low tBVWL 67 ns

WR pulse width low tWLWH 150 ns

WR low to RDY/BSY low tWLRL 0 1 µs

WR low to RDY/BSY high(1) tWLRH 3.7 4.5 ms

WR low to RDY/BSY high for chip erase(2) tWLRH_CE 7.5 9ms

XTAL1 low to OE low tXLOL 0ns

BS1 valid to DATA valid tBVDV 0250 ns

OE low to DATA valid tOLDV 250 ns

OE high to DATA tri-stated tOHDZ 250 ns

Notes: 1. tWLRH is valid for the Write Flash, Write EEPROM, Write Fuse bits and Write Lock bits commands.

2. tWLRH_CE is valid for the Chip Erase command.

XTAL1

PAGEL/BS1

DATA

XA0

XA1/BS2

tXLOL

tOLDV

tOHDZ

tBVDV

Load Address

(Low Byte)

Read Data

(Low Byte)

Read Data

(High Byte)

Load Address

(Low Byte)

ADDR0 (Low Byte) ADDR1 (Low Byte)DATA (Low Byte) DATA (High Byte)

Note: AtmeL In SPI programming mode khe minimum SCK high/low period Is: fﬁ \)

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22.10 SPI Timing Characteristics

See Figure 22-6 and Figure 22-7 on page 232 for details.

Figure 22-6. SPI Interface Timing Requirements (Master Mode)

Table 22-12. SPI Timing Parameters

Description Mode Min. Typ. Max.

1SCK period Master See Table 13-4 on page 135

2SCK high/low Master 50% duty cycle

3Rise/fall time Master 3.6

4Setup Master 10

5Hold Master 10

6Out to SCK Master 0.5 • tsck

7SCK to out Master 10

8SCK to out high Master 10

9SS low to out Slave 15

10 SCK period Slave 4 • tck

11 SCK high/low (1) Slave 2 • tck

12 Rise/fall time Slave 1.6 µs

13 Setup Slave 10

14 Hold Slave tck

15 SCK to out Slave 15

16 SCK to SS high Slave 20

17 SS high to tri-state Slave 10

18 SS low to SCK Slave 2 • tck

Note: In SPI programming mode the minimum SCK high/low period is:

- 2 tCLCL for fCK < 12MHz

- 3 tCLCL for fCK >12MHz

MSB

SCK

(CPOL = 0)

SCK

(CPOL = 1)

MISO

(Data Input)

MOSI

(Data Output) MSB LSB

LSB

...

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232

Figure 22-7. SPI Interface Timing Requirements (Slave Mode)

MSB

SCK

(CPOL = 0)

SCK

(CPOL = 1)

MOSI

(Data Input)

MISO

(Data Output) MSB LSB

LSB

...

13 14

10 16

11 11

AtmeL

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23. Decoupling Capacitors

The operating frequency (i.e. system clock) of the processor determines in 95% of cases the value needed for

microcontroller decoupling capacitors.

The hypotheses used as first evaluation for decoupling capacitors are:

●The operating frequency (fop) supplies itself the maximum peak levels of noise. The main peaks are located at fop and

2 fop.

●An SMC capacitor connected to 2 micro-vias on a PCB has the following characteristics:

●1.5 nH from the connection of the capacitor to the PCB,

●1.5 nH from the capacitor intrinsic inductance.

Figure 23-1. Capacitor description

According to the operating frequency of the product, the decoupling capacitances are chosen considering the frequencies to

filter, fop and 2 fop.

The relation between frequencies to cut and decoupling characteristics are defined by:

and

where:

●L: the inductance equivalent to the global inductance on the Vcc/Gnd lines.

●C1 and C2: decoupling capacitors (C1 = 4 C2).

Then, in normalized value range, the decoupling capacitors become:

These decoupling capacitors must to be implemented as close as possible to each pair of power supply pins:

●16-17 for logic sub-system,

●5-6 for analogical sub-system.

Nevertheless, a bulk capacitor of 10-47µF is also needed on the power distribution network of the PCB, near the power

source.

For further information, please refer to application notes AVR® 040 “EMC design considerations” and AVR042 “hardware

design considerations” on the Atmel® web site.

Table 23-1. Decoupling Capacitors versus Frequency

fop , operating frequency C1C2

16MHz 33nF 10nF

12MHz 56nF 15nF

10MHz 82nF 22nF

8MHz 120nF 33nF

6MHz 220nF 56nF

4MHz 560nF 120nF

PCB

Capacitor

1.5 nH

0.75 nH 0.75 nH

fop 1

2LC1

---------------------

2fop1

2LC2

---------------------

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24. Typical Characteristics

The data contained in this section is largely based on simulations and characterization of similar devices in the same

process and design methods. Thus, the data should be treated as indications of how the part will behave.

The following charts show typical behavior. These figures are not tested during manufacturing. All current consumption

measurements are performed with all I/O pins configured as inputs and with internal pull-ups enabled. A sine wave generator

with rail-to-rail output is used as clock source.

The power consumption in power-down mode is independent of clock selection.

The current consumption is a function of several factors such as: operating voltage, operating frequency, loading of I/O pins,

switching rate of I/O pins, code executed and ambient temperature. The dominating factors are operating voltage and

frequency.

The current drawn from capacitive loaded pins may be estimated (for one pin) as CL Vcc f where CL= load capacitance,

Vcc = operating voltage and f = average switching frequency of I/O pin.

The parts are characterized at frequencies higher than test limits. Parts are not guaranteed to function properly at

frequencies higher than the ordering code indicates.

The difference between current consumption in power-down mode with watchdog timer enabled and power-down mode with

watchdog timer disabled represents the differential current drawn by the watchdog timer.

24.1 Active Supply Current

Figure 24-1. Active Supply Current versus Low Frequency (0.1 - 1.0MHz)

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

1.4

1.2

1.0

0.8

0.6

0.4

0.2

6.0

5.5

5.0

4.5

4.0

3.6

3.3

3.0

2.7

2.4

2.1

2.0

Frequency (MHz)

ICC (mA)

1.8

1.6

AtmeL / // + / k // + // + $C///ﬁ? : :éé/ + ‘+++|‘+‘

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Figure 24-2. Active Supply Current versus Frequency (≥ 1MHz)

Figure 24-3. Active Supply Current versus VCC (Internal RC Oscillator, 8MHz)

Figure 24-4. Active Supply Current versus VCC (Internal RC Oscillator, 128kHz)

0 2 4 6 8 10 12 14 16 18 20

Frequency (MHz)

(mA)

6.0

5.5

5.0

4.5

4.0

3.6

3.3

3.0

2.7

2.4

1.5 2 2.5 3 3.5 4 4.5 5 5.5

ICC (mA)

VCC (V)

150

125

-40

1.5 2 2.5 3 3.5 4 4.5 5 5.5

0.18

0.20

0.16

0.14

0.12

0.10

0.08

0.06

0.04

0.02

ICC (mA)

VCC (V)

150

125

-40

‘+HH‘ AtmeL

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24.2 Idle Supply Current

Figure 24-5. Idle Supply Current versus Frequency (≥ 1MHz)

Figure 24-6. Idle Supply Current versus VCC (Internal RC Oscillator, 8MHz)

Figure 24-7. Idle Supply Current versus VCC (Internal RC Oscillator, 128kHz)

0 2 4 6 8 10 12 14 16 18 20

Frequency (MHz)

(mA)

6.0

5.5

5.0

4.5

4.0

3.6

3.3

3.0

2.7

2.4

2.5

1.5

0.5

(mA)

1.5 2 2.5 3 3.5 4 4.5 5 5.5

(V)

150

125

-40

1.5 2 2.5 3 3.5 4 4.5 5 5.5

0.07

0.08

0.06

0.05

0.04

0.03

0.02

0.01

ICC (mA)

VCC (V)

150

125

-40

AtmeL

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24.3 Supply Current of I/O modules

The table below can be used to calculate the additional current consumption for the different I/O modules idle mode. The

enabling or disabling of the I/O modules are controlled by the power reduction register. See Section 5.9.3 “PRR – Power

Reduction Register” on page 46 for details.

24.4 Power-down Supply Current

Figure 24-8. Power-down Supply Current versus VCC (Watchdog Timer Disabled)

Figure 24-9. Power-down Supply Current versus VCC (Watchdog Timer Enabled)

Table 24-1. Additional Current Consumption for the different I/O modules (absolute values)

Module

Vcc = 5.0V

Freq. = 16MHz

Vcc = 5.0V

Freq. = 8MHz

Vcc = 3.0V

Freq. = 8MHz

Vcc = 3.0V

Freq. = 4MHz Units

LIN/UART 0.77 0.37 0.20 0.10 mA

SPI 0.31 0.14 0.08 0.04 mA

TIMER-1 0.28 0.13 0.08 0.04 mA

TIMER-0 0.41 0.20 0.10 0.05 mA

USI 0.14 0.05 0.04 0.02 mA

ADC 0.48 0.22 0.10 0.05 mA

1.5 2 2.5 3 3.5 4 4.5 5 5.5

ICC (µA)

VCC (V)

150

125

-40

1.5 2 2.5 3 3.5 4 4.5 5 5.5

ICC (µA)

VCC (V)

150

125

-40

+HH HM} ‘+HH‘ AtmeL

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238

24.5 Pin Pull-up

Figure 24-10. I/O Pin pull-up Resistor Current versus Input Voltage (VCC = 2.7V)

Figure 24-11. I/O Pin pull-up Resistor Current versus Input Voltage (VCC = 5V)

Figure 24-12. Reset Pull-up Resistor Current versus Reset Pin Voltage (VCC = 2.7V)

00.5 1.5122.53

-10

IOP (µA)

VOP (V)

150

125

-40

01 32 456

140

160

120

100

-20

IOP (µA)

VOP (V)

150

125

-40

00.5 1.5122.53

-10

IRESET (µA)

VRESET (V)

150

125

-40

AtmeL ‘+HH‘ ‘+HH‘

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ATtiny87/ATtiny167 [DATASHEET]

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Figure 24-13. Reset Pull-up Resistor Current versus Reset Pin Voltage (VCC = 5V)

24.6 Pin Driver Strength

Figure 24-14. I/O Pin Output Voltage versus Sink Current (VCC = 3V)

Figure 24-15. I/O Pin Output Voltage versus Sink Current (VCC = 5V)

01 32456

120

100

-20

IRESET (µA)

VRESET (V)

150

125

-40

0 2 4 6 8 10 12 14 16 18

1.8

2.0

1.6

1.4

1.2

1.0

0.8

0.6

0.4

0.2

VOL (V)

IOL (mA)

150

125

-40

0 5 10 15 20 25

1.2

1.0

0.8

0.6

0.4

0.2

(V)

(mA)

150

125

-40

“Rx \$\\ : \:\\\ : K\ + K \-\\ : \\\ \\\ + \\\ + \ Vm 1V! AtmeL

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Figure 24-16. I/O Pin Output Voltage versus Source Current (VCC = 3V)

Figure 24-17. I/O Pin Output Voltage versus Source Current (VCC = 5V)

24.7 Internal Oscillator Speed

Figure 24-18. Calibrated 8.0MHz RC Oscillator Frequency versus Vcc

0 2 4 6 8 101214161820

3.0

2.5

2.0

1.5

1.0

0.5

VOH (V)

IOH (mA)

150

125

-40

0 2 4 6 8 101214161820

5.1

4.9

4.7

4.5

4.3

4.1

3.9

3.7

VOH (V)

IOH (mA)

150

125

-40

*15u __125 FM [MHz] , 25 +740 a 15 32 AB 6‘ an as 112 123 m «an 175 192 m 224 2-10 OSCCALOG) MM \ \ AtmeL

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Figure 24-19. Calibrated 8.0MHz RC Oscillator Frequency versus OSCCAL Value

24.8 Current Consumption in Reset

Figure 24-20. Reset Supply Current versus Vcc, Frequencies 0.1 - 1.0MHz

(Excluding Current Through the Reset Pull-up)

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

0.30

0.25

0.20

0.15

0.10

0.05

ICC (mA)

Frequency (MHz)

6.0

5.5

5.0

4.5

4.0

3.6

3.3

3.0

2.7

2.4

2.1

2.0

1.8

1.6

AtmeL

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Figure 24-21. Reset Supply Current versus Vcc, Frequencies ≥ 1MHz

(Excluding Current Through the Reset Pull-up)

0 2 4 6 8 1012 14161820

4.5

4.0

3.5

3.0

2.5

2.0

1.5

1.0

0.5

(mA)

Frequency (MHz)

6.0

5.5

5.0

4.5

4.0

3.6

3.3

3.0

2.7

2.4

2.1

2.0

1.8

1.6

Address Bit 5 Bil 2 oes. . ress \sexcee mg a e , on page are on care. AtmeL

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25. Register Summary

Address Name Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 Page

(0xFF) Reserved

(0xFE) Reserved

(0xFD) Reserved

(0xFC) Reserved

(0xFB) Reserved

(0xFA) Reserved

(0xF9) Reserved

(0xF8) Reserved

(0xF7) Reserved

(0xF6) Reserved

(0xF5) Reserved

(0xF4) Reserved

(0xF3) Reserved

(0xF2) Reserved

(0xF1) Reserved

(0xF0) Reserved

(0xEF) Reserved

(0xEE) Reserved

(0xED) Reserved

(0xEC) Reserved

(0xEB) Reserved

(0xEA) Reserved

(0xE9) Reserved

(0xE8) Reserved

(0xE7) Reserved

(0xE6) Reserved

(0xE5) Reserved

(0xE4) Reserved

(0xE3) Reserved

(0xE2) Reserved

(0xE1) Reserved

(0xE0) Reserved

(0xDF) Reserved

(0xDE) Reserved

(0xDD) Reserved

(0xDC) Reserved

Notes: 1. Address bits exceeding EEAMSB (Table 21-8 on page 210) are don’t care.

2. For compatibility with future devices, reserved bits should be written to zero if accessed. Reserved I/O memory

addresses should never be written.

3. I/O registers within the address range 0x00 - 0x1F are directly bit-accessible using the SBI and CBI instructions. In these

registers, the value of single bits can be checked by using the SBIS and SBIC instructions.

4. Some of the status flags are cleared by writing a logical one to them. Note that, unlike most other AVRs, the CBI and SBI

instructions will only operate on the specified bit, and can therefore be used on registers containing such status flags.

The CBI and SBI instructions work with registers 0x00 to 0x1F only.

5. When using the I/O specific commands IN and OUT, the I/O addresses 0x00 - 0x3F must be used. When addressing I/O

registers as data space using LD and ST instructions, 0x20 must be added to these addresses. The Atmel®

ATtiny87/167 is a complex microcontroller with more peripheral units than can be supported within the 64 location

reserved in opcode for the IN and OUT instructions. For the extended I/O space from 0x60 - 0xFF in SRAM, only the

ST/STS/STD and LD/LDS/LDD instructions can be used.

Address Namo Bit 7 Bi! 5 Bit 4 Bit 3 Bit 2 ress \ exce mg , on page are on care. AtmeL

ATtiny87/ATtiny167 [DATASHEET]

7728H–AVR–03/14

244

(0xDB) Reserved

(0xDA) Reserved

(0xD9) Reserved

(0xD8) Reserved

(0xD7) Reserved

(0xD6) Reserved

(0xD5) Reserved

(0xD4) Reserved

(0xD3) Reserved

(0xD2) LINDAT LDATA7 LDATA6 LDATA5 LDATA4 LDATA3 LDATA2 LDATA1 LDATA0 171

(0xD1) LINSEL –––– /LAINC LINDX2 LINDX1 LINDX0 171

(0xD0) LINIDR LP1 LP0 LID5 / LDL1 LID4 /

LDL0 LID3 LID2 LID1 LID0 170

(0xCF) LINDLR LTXDL3 LTXDL2 LTXDL1 LTXDL0 LRXDL3 LRXDL2 LRXDL1 LRXDL0 170

(0xCE) LINBRRH –––– LDIV11 LDIV10 LDIV9 LDIV8 170

(0xCD) LINBRRL LDIV7 LDIV6 LDIV5 LDIV4 LDIV3 LDIV2 LDIV1 LDIV0 170

(0xCC) LINBTR LDISR – LBT5 LBT4 LBT3 LBT2 LBT1 LBT0 169

(0xCB) LINERR LABORT LTOERR LOVERR LFERR LSERR LPERR LCERR LBERR 168

(0xCA) LINENIR –––– LENERR LENIDOK LENTXOK LENRXOK 168

(0xC9) LINSIR LIDST2 LIDST1 LIDST0 LBUSY LERR LIDOK LTXOK LRXOK 167

(0xC8) LINCR LSWRES LIN13 LCONF1 LCONF0 LENA LCMD2 LCMD1 LCMD0 166

(0xC7) Reserved

(0xC6) Reserved

(0xC5) Reserved

(0xC4) Reserved

(0xC3) Reserved

(0xC2) Reserved

(0xC1) Reserved

(0xC0) Reserved

(0xBF) Reserved

(0xBE) Reserved

(0xBD) Reserved

(0xBC) USIPP USIPOS 148

(0xBB) USIBR USIB7 USIB6 USIB5 USIB4 USIB3 USIB2 USIB1 USIB0 145

(0xBA) USIDR USID7 USID6 USID5 USID4 USID3 USID2 USID1 USID0 144

(0xB9) USISR USISIF USIOIF USIPF USIDC USICNT3 USICNT2 USICNT1 USICNT0 145

(0xB8) USICR USISIE USIOIE USIWM1 USIWM0 USICS1 USICS0 USICLK USITC 146

25. Register Summary (Continued)