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  • 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.

    Key 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

Circuit Diagram

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Technical Documentation

    • Description Version Size Action
      DS2149
      Serial access real-time clock with alarm
      11.0
      583.32 KB
      PDF
      DS2149

      Serial access real-time clock with alarm

    • Description Version Size Action
      AN3060
      Applications guide for serial real-time clocks (RTCs)
      3.0
      878.56 KB
      PDF
      AN1011
      Battery technology used in NVRAM and real-time clock (RTC) products from ST
      4.0
      248.17 KB
      PDF
      AN934
      How to use the digital calibration feature in TIMEKEEPER® and serial real-time clock (RTC) products
      4.1
      123.42 KB
      PDF
      AN1216
      Implementing a periodic alarm with TIMEKEEPER® and serial real-time clocks (RTCs)
      2.0
      192.89 KB
      PDF
      AN4641
      Integrating TIMEKEEPER® and real-time clock supervisor functions
      1.0
      479.28 KB
      PDF
      AN923
      Managing century information using serial real-time clocks and TIMEKEEPER® NVRAMs
      4.0
      142.23 KB
      PDF
      AN1572
      Power-down time-stamp function in serial real-time clocks (RTCs)
      2.0
      171.31 KB
      PDF
      AN1336
      Power-fail comparator for NVRAM supervisory devices
      2.0
      127.81 KB
      PDF
      AN1012
      Predicting the battery life and data retention period of NVRAMs and serial RTCs
      4.1
      439.45 KB
      PDF
      AN922
      Using a Super Cap to back up the M41T56, M41T00, M41T11, M41T81, M41T94, and M41ST84W (16-pin)
      2.1
      84.5 KB
      PDF
      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)

HW Model, CAD Libraries & SVD

    • Description Version Size Action
      Ibis model 1.0
      8.28 KB
      ZIP

      Ibis model

Publications and Collaterals

    • Description Version Size Action
      Serial real-time clock ICs 1.0
      827.11 KB
      PDF

      Serial real-time clock ICs

Quality and Reliability

Part Number Marketing Status Package Grade RoHS Compliance Grade Material Declaration**
M41T81M6F
Active
SO-8 Industrial Ecopack1

M41T81M6F

Package:

SO-8

Material Declaration**:

PDF XML

Marketing Status

Active

Package

SO-8

Grade

Industrial

RoHS Compliance Grade

Ecopack1

(**) 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.

Sample & Buy

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M41T81M6F Available at 7 distributors

Distributor availability ofM41T81M6F

Distributor Name
Region Stock Min. Order Third party link
DIGIKEY WORLDWIDE 7642 1 Order Now
COMPEL EUROPE 2983 1 Order Now
RS COMPONENTS EUROPE 3270 1 Order Now
FUTURE WORLDWIDE 731 1 Order Now
ARROW AMERICA 31500 1 Order Now
MOUSER WORLDWIDE 3495 1 Order Now
Farnell Element14 EUROPE 2118 1 Order Now

Distributor reported inventory date: 2020-09-18

Distributor Name

DIGIKEY

Stock

7642

Min.Order

1

Region

WORLDWIDE Order Now

COMPEL

Stock

2983

Min.Order

1

Region

EUROPE Order Now

RS COMPONENTS

Stock

3270

Min.Order

1

Region

EUROPE Order Now

FUTURE

Stock

731

Min.Order

1

Region

WORLDWIDE Order Now

ARROW

Stock

31500

Min.Order

1

Region

AMERICA Order Now

MOUSER

Stock

3495

Min.Order

1

Region

WORLDWIDE Order Now

Farnell Element14

Stock

2118

Min.Order

1

Region

EUROPE Order Now

Distributor reported inventory date: 2020-09-18

Buy now
Active
EAR99 NEC Tape And Reel SO-8 -40 85 1.106 / 1k
MORE INFO

NVRAM size (B):

-

Country of Origin:

MOROCCO

M41T81M6F

Marketing Status

Active

ECCN (US)

EAR99

Budgetary Price (US$)*/Qty

1.106 / 1k

Distributor availability ofM41T81M6F

Distributor Name
Region Stock Min. Order Third party link
DIGIKEY WORLDWIDE 7642 1 Order Now
COMPEL EUROPE 2983 1 Order Now
RS COMPONENTS EUROPE 3270 1 Order Now
FUTURE WORLDWIDE 731 1 Order Now
ARROW AMERICA 31500 1 Order Now
MOUSER WORLDWIDE 3495 1 Order Now
Farnell Element14 EUROPE 2118 1 Order Now

Distributor reported inventory date: 2020-09-18

Distributor Name

DIGIKEY

Stock

7642

Min.Order

1

Region

WORLDWIDE Order Now

COMPEL

Stock

2983

Min.Order

1

Region

EUROPE Order Now

RS COMPONENTS

Stock

3270

Min.Order

1

Region

EUROPE Order Now

FUTURE

Stock

731

Min.Order

1

Region

WORLDWIDE Order Now

ARROW

Stock

31500

Min.Order

1

Region

AMERICA Order Now

MOUSER

Stock

3495

Min.Order

1

Region

WORLDWIDE Order Now

Farnell Element14

Stock

2118

Min.Order

1

Region

EUROPE Order Now

Distributor reported inventory date: 2020-09-18

ECCN (EU)

NEC

Packing Type

Tape And Reel

Package

SO-8

Operating Temperature (°C)

(min)

-40

(max)

85

Budgetary Price (US$)* / Qty

1.106 / 1k

NVRAM size (B)

-

Country of Origin

MOROCCO

(*) Suggested Resale Price per unit (USD) for BUDGETARY USE ONLY. For quotes, prices in local currency, please contact your local ST Sales Office  or our Distributors