The DS1302 trickle-charge timekeeping chip contains a real-time clock/calendar and 31 bytes of static RAM. It communicates with a microprocessor via a simple serial interface.
Only three wires are required to communicate with the clock/RAM: CE (chip enable), I/O (data line) and SCLK (serial clock). Data can be transfered to and from the clock/RAM 1 byte at a time, or in a burst of up to 31 bytes. The DS1302 is designed to operate on very low power, and retain the data and clock information on less than 1 µW.
A 32.768 kHz (+/- 20ppm) Cylindrical Crystal with a 6 pF load capacitance is included.