ST M41T00S handbook
Datasheet
The M41T00S is a serial real-time clock with 2.0 to 5.5 V clock operating voltage, counters for seconds, minutes, hours, day, date, month, year, and century, software clock calibration, automatic switchover and deselect circuitry, low operating current of 300 µA, oscillator stop detection, battery or SuperCap™ backup, -40 to 85 °C operating temperature and ultra-low battery supply current of 0.6 µA.