The M41T81 is a low-power serial RTC with a built-in 32.768 kHz oscillator (external crystal controlled). Eight bytes of the SRAM are used for the clock/calendar function and are configured in binary-coded decimal (BCD) format. An additional 12 bytes of SRAM provide status/control of alarm, watchdog and square wave functions. Addresses and data are transferred serially via a two line, bidirectional I2C interface. The built-in address register is incremented automatically after each WRITE or READ data byte.
The M41T81 has a built-in power sense circuit which detects power failures and automatically switches to the battery supply when a power failure occurs. The energy needed to sustain the SRAM and clock operations can be supplied by a small lithium button supply when a power failure occurs.
Functions available to the user include a non-volatile, time-of-day clock/calendar, alarm interrupts, watchdog timer and programmable square wave output. The eight clock address locations contain the century, year, month, date, day, hour, minute, second and tenths/hundredths of a second in 24-hour BCD format. Corrections for 28, 29 (leap year - valid until year 2100), 30 and 31 day months are made automatically.
The M41T81 is supplied in an 8-pin SOIC.
For all new designs use M41T81S
Counters for tenths/hundredths of seconds, seconds, minutes, hours, day, date, month, year, and century
32 KHz crystal oscillator integrating load capacitance (12.5 pF) providing exceptional oscillator stability and high crystal series resistance operation
Serial interface supports I2C bus (400 kHz protocol)
Ultra-low battery supply current of 0.6 μA (typ at 3 V)
2.0 to 5.5 V clock operating voltage
Automatic switchover and deselect circuitry (for 3 V application select M41T81S datasheet)
Power-down time stamp (HT bit) allowing determination of time elapsed in battery backup
Programmable alarm and interrupt function (valid even during battery backup mode)
Accurate programmable watchdog timer (from 62.5 ms to 128 s)
Software clock calibration to compensate crystal deviation due to temperature
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