The DS1677 portable system controller is a circuit that incorporates many of the functions necessary for low-power portable products integrated into one chip. The device provides a real-time clock (RTC), NV RAM controller, microprocessor monitor, power-fail warning, and a 3-channel, 8-bit analog-to-digital converter (ADC). Communication with the DS1677 is established through a simple 3-wire interface. The RTC provides seconds, minutes, hours, day, date, month, and year information with leap year compensation. The RTC also provides an alarm interrupt. This interrupt works when the DS1677 is powered by the system power supply or when in battery-backup operation so the alarm can be used to wake up a system that is powered down. Automatic backup and write protection of an external SRAM is provided through the VCCO and CEO pins. The backup energy source used to power the RTC is also used to retain RAM data in the absence of VCC through the VCCO pin. CEO, the chip-enable output to SRAM, is controlled during power transients to prevent data corruption.