Power-up reset conditioned on direction of voltage change

摘要

A system which includes a microprocessor (or microcontroller) and an auxiliary chip which monitors the system power supply voltage and performs related functions for the microprocessor. In one mode of operation (for use with a low-power CMOS processor), the auxiliary chip sends an interrupt to the microprocessor when the power supply falls to a first level, and also resets the microprocessor when the supply voltage reaches a second preset level on the way up (i.e. while power is being restored). In a selectable second mode of operation (for use with NMOS processor), the auxiliary chip resets the processor when the power supply is on the way down.