The Analog Devices DS1302ZN is a real-time clock/calendar chip with 31 bytes of battery-backed RAM. It features a simple 3-wire serial interface and operates over a wide voltage range.
The Analog Devices DS1302ZN+T&R is a Real-Time Clock/Calendar IC with 31 bytes of battery-backed RAM. It features a simple 3-wire serial interface and operates from 2V to 5.5V.