The DS1642 is a 2K x 8 nonvolatile static RAM and a full-function real time clock which are both accessible in a bytewide format. The nonvolatile time keeping RAM is pin- and function-equivalent to any JEDEC standard 2K x 8 SRAM. The device can also be easily substituted in ROM, EPROM and EEPROM sockets, providing read/write nonvolatility and the addition of the real time clock function. The real time clock information resides in the eight uppermost RAM locations. The RTC registers contain year, month, date, day, hours, minutes, and seconds data in 24-hour BCD format. Corrections for the day of the month and leap year are made automatically. The RTC clock registers are double-buffered to avoid access of incorrect data that can occur during clock update cycles. The double-buffered system also 1 of 11