The Portable System Controller is a circuit, which incorporates many of the functions necessary for low power portable products integrated into one chip. The DS1670 provides a Real Time Clock, NV RAM controller, microprocessor monitor, and a 3-channel, 8-bit analog-to-digital converter. Communication with the DS1670 is established through a simple 3-wire interface. The Real Time Clock (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 DS1670 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, CEOL , and CEOH 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. The chip-enable outputs to RAM ( CEOL and CEOH ) are controlled during power transients to prevent data corruption. 1 of 17