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
- Operating temperature of –40 to 85 °C
- ECOPACK®package available
(**) The Material Declaration forms available on st.com may be generic documents based on the most commonly used package within a package family. For this reason, they may not be 100% accurate for a specific device. Please contact our sales support for information on specific devices.