Parallel RTC with 242 bytes of NVSRAM
The Maxim Integrated DS1687-3+ is a parallel-interface real-time clock and calendar with 242 bytes of nonvolatile SRAM integrated into a single 24-pin EDIP module. It tracks time in HH:MM:SS (12/24-hour) and date in YY-MM-DD-dd format, includes alarm, square-wave output, and Y2K compliance. The through-hole 24-DIP module (0.600-inch body) is socket-friendly — a part you can swap on site with a chip puller and no hot air.
Supply range and battery backup
Runs from a 2.7 V to 3.7 V main supply, with a separate battery input accepting 2.5 V to 3.7 V. Timekeeping current draws 2 mA max at 3 V — modest for a parallel RTC with embedded NVSRAM. The battery pin keeps the clock and the 242-byte SRAM alive when the main rail drops; a 3 V lithium coin cell (CR2032 or equivalent) is the typical choice.