The DS1688/DS1691 is a real-time clock (RTC) designed as a successor to the industry standard DS1285, DS1385, DS1485, and DS1585 PC real time clocks. This device provides the industry standard DS1285 clock function with the new feature of either +3.0 or +5.0V operation and automatic backup and write protection to an external SRAM. The DS1688 also incorporates a number of enhanced features including a silicon serial number, power on/off control circuitry, 114 bytes of user NV SRAM, power on elapsed timer, and power cycle counter. * +3 or +5V operation * 64-bit Silicon serial number * 64-bit customer specific ROM or additional serial number available * Power control circuitry supports system power on from date/time alarm or key closure * Automatic battery backup and write protection to external SRAM * Crystal select bit allows RTC to operate with * 6pF or 12.5pF crystal * 114 bytes user NV RAM * Auxiliary battery input * RAM clear input * Century register * 32kHz output for power management * 32-bit VCC powered elapsed time counter * 32-bit VBAT powered elapsed time counter * 16-bit power cycle counter * Compatible with existing BIOS for original DS1287 functions * Available as IC (DS1688) or stand-alone module with embedded battery and crystal (DS1691) * Timekeeping algorithm includes leap year compensation valid up to 2100