The ADM803/ADM809/ADM810 supervisory circuits monitor the power supply voltage in microprocessor systems. They pro vide a reset output during power-up, power-down, and brownout conditions. On power-up, an internal timer holds reset asserted for 240 ms. This holds the microprocessor in a reset state until conditions have stabilized. The RESET output remains opera tional with VCC as low as 1 V. The ADM803 and ADM809 provide an active low reset signal (RESET), while the ADM810 provides an active high signal (RESET) output. The ADM809 and ADM810 have push-pull outputs, whereas the ADM803 has an open-drain output, which requires an external pull-up resistor.