23.4.6.1 Raising the Backup Power Supply

When the backup voltage VDDIO rises, the slow RC oscillator is powered up and the zero-power power-on reset cell maintains its output low as long as VDDIO has not reached its target voltage. During this period, the SUPC is reset. When the VDDIO voltage becomes valid and the zero-power power-on reset signal is released, a counter is started for five slow clock cycles. This is the time required for the slow RC oscillator to stabilize.

After this time, the voltage regulator is enabled. The core power supply rises and the brownout detector provides the bodcore_in signal as soon as the core voltage VDDCORE is valid. This results in releasing the vddcore_nreset signal to the Reset Controller after the bodcore_in signal has been confirmed as being valid for at least one slow clock cycle.