The Portable System Controller is a circuit which incorporates many of the functions necessary for low power portable products integrated into one chip. The DS1673 provides a Real Time Clock, NV RAM controller, microprocessor monitor, and a 3-channel, 8-bit analog-to-digital converter. Communication with the DS1673 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 DS1673 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.