The CMOS bq3285 is a low-power microprocessor peripheral providing a time-of-day clock and 100-year calendar with alarm features and battery operation. Other features include three maskable interrupt sources, square wave output, and 114 bytes of general nonvolatile storage. The bq3285 write-protects the clock, calendar, and storage registers during power failure. A backup battery then maintains data and operates the clock and calendar. The bq3285 is a fully compatible real-time clock for IBM AT compatible computers and other applications. The only external components are a 32.768kHz crystal and a backup battery.