The hibernation module controls power to the microcontroller through the use of the HIB pin, which is intended to be connected to the enable signal of the external regulator providing 3.3 V to the microcontroller and other circuits. When the HIB signal is asserted by the hibernation module, the external regulator is turned off and no longer powers the microcontroller and any parts of the system that are powered by the regulator. The hibernation module remains powered from the VBAT supply, which could be a battery or an auxiliary power source, until a wake event. Power to the microcontroller is restored by de-asserting the HIB signal, which causes the external regulator to turn power back on to the chip. The hibernation module may also be configured to cut power to all internal modules. While in this state, all pins are held in the state they were in, prior to entering hibernation. This is also called VDD3ON mode, and in this mode, the state of GPIO pins is retained while the device is in the hibernation mode.