M41T81M6F Real-Time Clock (RTC) ICs by STMicroelectronics

Serial real-time clock (RTC) with alarm


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 I 2 C 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.

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Features

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

Resources


Application Notes
AN3060 Applications guide for serial real-time clocks (RTCs)
AN1011 Battery technology used in NVRAM and real-time clock (RTC) products from ST
AN934 How to use the digital calibration feature in TIMEKEEPER® and serial real-time clock (RTC) products
AN1216 Implementing a periodic alarm with TIMEKEEPER® and serial real-time clocks (RTCs)
AN4641 Integrating TIMEKEEPER® and real-time clock supervisor functions
AN923 Managing century information using serial real-time clocks and TIMEKEEPER® NVRAMs
AN1572 Power-down time-stamp function in serial real-time clocks (RTCs)
AN1336 Power-fail comparator for NVRAM supervisory devices
AN1012 Predicting the battery life and data retention period of NVRAMs and serial RTCs
AN922 Using a Super Cap to back up the M41T56, M41T00, M41T11, M41T81, M41T94, and M41ST84W (16-pin)



Frequently Asked Questions

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Additional datasheets, footprints and schematics for M41T81M6F are listed on our Part Details page. You can also find images and similar parts to M41T81M6F on this page.

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What category does M41T81M6F fall under?

The M41T81M6F is listed under Clocks and Timers > Real-Time Clock (RTC) ICs > RTC - Serial Interface.

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You can view similar parts to M41T81M6F when available in the RTC - Serial Interface range under the specifications section at the bottom of the details page.

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Is the M41T81M6F RoHS compliant?

Yes. This part has been flagged as RoHS Compliant by STMicroelectronics.

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