Microprocessor supervisors

ST’s microprocessor supervisors are more sophisticated devices that can include watchdog and early power-fail warnings (power-fail in/power-fail out (PFI/PFO)), push-button reset functions and battery monitoring. 
Microprocessor supervisors with a switchover function preserve SRAM data in the absence of system power by automatically switching to batter backup when power fails.  A chip-enable gate automatically write-protects the SRAM when the Vcc begins to fall.