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  • The M41T81S is a low-power serial real-time clock (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 M41T81S 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 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 M41T81S is supplied in either an 8-pin SOIC or an 18-pin 300 mil SOIC package which includes an embedded 32 KHz crystal.
    The 18-pin, embedded crystal SOIC requires only a user-supplied battery to provide non-volatile operation.

    Key Features

    • Counters for tenths/hundredths of seconds, seconds, minutes, hours, day, date, month, year, and century
    • 32 KHz crystal oscillator with integrated load capacitance (12.5 pf) which provides exceptional oscillator stability and high crystal series resistance operation)
    • Oscillator stop detection (monitors clock operation)
    • Serial interface supports I2C bus (400 kHz protocol)
    • Ultra-low battery supply current of 0.6 μA (typ)
    • 2.0 to 5.5 V clock operating voltage
    • Automatic switchover and deselect circuitry (fixed reference) which provides full operation in 3.0 V applications)
    • VCC= 2.7 to 5.5 V
    • 2.5 V ≤ VPFD≤ 2.7 V
    • Power-down time-stamp (HT bit) which allows determination of time elapsed in battery backup
    • Battery low flag
    • 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 for crystal deviation due to temperature)
    • Operating temperature of –40 to 85 °C
    • Package options include an 8-lead SOIC or 18-lead embedded crystal SOIC

Circuit Diagram

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Technical Documentation

    • Description Version Size Action
      DS4003
      Serial access real-time clock (RTC) with alarms
      7.0
      501.8 KB
      PDF
      DS4003

      Serial access real-time clock (RTC) with alarms

    • 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
      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

HW Model, CAD Libraries & SVD

    • Description Version Size Action
      M41T81S IBIS model 1.0
      9.85 KB
      ZIP

      M41T81S 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**
M41T81SM6F
Active
SO-8 Industrial Ecopack1
M41T81SMY6F
Active
SO18 with embedded crystal Industrial Ecopack1

M41T81SM6F

Package:

SO-8

Material Declaration**:

PDF XML

Marketing Status

Active

Package

SO-8

Grade

Industrial

RoHS Compliance Grade

Ecopack1

M41T81SMY6F

Package:

SO18 with embedded crystal

Material Declaration**:

PDF XML

Marketing Status

Active

Package

SO18 with embedded crystal

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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More info
min
max
M41T81SM6F Available at 9 distributors

Distributor availability ofM41T81SM6F

Distributor Name
Region Stock Min. Order Third party link
DIGIKEY WORLDWIDE 3685 1 Order Now
COMPEL EUROPE 1324 1 Order Now
RS COMPONENTS EUROPE 4855 5 Order Now
AVNET AMERICA 55080 0 Order Now
FUTURE WORLDWIDE 1571 1 Order Now
ARROW EUROPE 7500 0 Order Now
ARROW AMERICA 50 1 Order Now
MOUSER WORLDWIDE 12780 1 Order Now
RUTRONIK EUROPE 2500 2500 Order Now

Distributor reported inventory date: 2020-08-13

Distributor Name

DIGIKEY

Stock

3685

Min.Order

1

Region

WORLDWIDE Order Now

COMPEL

Stock

1324

Min.Order

1

Region

EUROPE Order Now

RS COMPONENTS

Stock

4855

Min.Order

5

Region

EUROPE Order Now

AVNET

Stock

55080

Min.Order

0

Region

AMERICA Order Now

FUTURE

Stock

1571

Min.Order

1

Region

WORLDWIDE Order Now

ARROW

Stock

7500

Min.Order

0

Region

EUROPE Order Now

ARROW

Stock

50

Min.Order

1

Region

AMERICA Order Now

MOUSER

Stock

12780

Min.Order

1

Region

WORLDWIDE Order Now

RUTRONIK

Stock

2500

Min.Order

2500

Region

EUROPE Order Now

Distributor reported inventory date: 2020-08-13

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

NVRAM size (B):

-

Country of Origin:

MOROCCO

M41T81SMY6F Available at 4 distributors

Distributor availability ofM41T81SMY6F

Distributor Name
Region Stock Min. Order Third party link
DIGIKEY WORLDWIDE 2025 1 Order Now
FUTURE WORLDWIDE 2000 1000 Order Now
Newark Element14 AMERICA 852 0 Order Now
MOUSER WORLDWIDE 2695 1 Order Now

Distributor reported inventory date: 2020-08-13

Distributor Name

DIGIKEY

Stock

2025

Min.Order

1

Region

WORLDWIDE Order Now

FUTURE

Stock

2000

Min.Order

1000

Region

WORLDWIDE Order Now

Newark Element14

Stock

852

Min.Order

0

Region

AMERICA Order Now

MOUSER

Stock

2695

Min.Order

1

Region

WORLDWIDE Order Now

Distributor reported inventory date: 2020-08-13

Sample & Buy Buy now
Active
EAR99 NEC Tape And Reel SO18 with embedded crystal -40 85
MORE INFO

NVRAM size (B):

-

Country of Origin:

PHILIPPINES

M41T81SM6F

Marketing Status

Active

ECCN (US)

EAR99

Budgetary Price (US$)*/Qty

1.106 / 1k

Distributor availability ofM41T81SM6F

Distributor Name
Region Stock Min. Order Third party link
DIGIKEY WORLDWIDE 3685 1 Order Now
COMPEL EUROPE 1324 1 Order Now
RS COMPONENTS EUROPE 4855 5 Order Now
AVNET AMERICA 55080 0 Order Now
FUTURE WORLDWIDE 1571 1 Order Now
ARROW EUROPE 7500 0 Order Now
ARROW AMERICA 50 1 Order Now
MOUSER WORLDWIDE 12780 1 Order Now
RUTRONIK EUROPE 2500 2500 Order Now

Distributor reported inventory date: 2020-08-13

Distributor Name

DIGIKEY

Stock

3685

Min.Order

1

Region

WORLDWIDE Order Now

COMPEL

Stock

1324

Min.Order

1

Region

EUROPE Order Now

RS COMPONENTS

Stock

4855

Min.Order

5

Region

EUROPE Order Now

AVNET

Stock

55080

Min.Order

0

Region

AMERICA Order Now

FUTURE

Stock

1571

Min.Order

1

Region

WORLDWIDE Order Now

ARROW

Stock

7500

Min.Order

0

Region

EUROPE Order Now

ARROW

Stock

50

Min.Order

1

Region

AMERICA Order Now

MOUSER

Stock

12780

Min.Order

1

Region

WORLDWIDE Order Now

RUTRONIK

Stock

2500

Min.Order

2500

Region

EUROPE Order Now

Distributor reported inventory date: 2020-08-13

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

M41T81SMY6F

Marketing Status

Active

ECCN (US)

EAR99

Budgetary Price (US$)*/Qty

Distributor availability ofM41T81SMY6F

Distributor Name
Region Stock Min. Order Third party link
DIGIKEY WORLDWIDE 2025 1 Order Now
FUTURE WORLDWIDE 2000 1000 Order Now
Newark Element14 AMERICA 852 0 Order Now
MOUSER WORLDWIDE 2695 1 Order Now

Distributor reported inventory date: 2020-08-13

Distributor Name

DIGIKEY

Stock

2025

Min.Order

1

Region

WORLDWIDE Order Now

FUTURE

Stock

2000

Min.Order

1000

Region

WORLDWIDE Order Now

Newark Element14

Stock

852

Min.Order

0

Region

AMERICA Order Now

MOUSER

Stock

2695

Min.Order

1

Region

WORLDWIDE Order Now

Distributor reported inventory date: 2020-08-13

ECCN (EU)

NEC

Packing Type

Tape And Reel

Package

SO18 with embedded crystal

Operating Temperature (°C)

(min)

-40

(max)

85

Budgetary Price (US$)* / Qty

NVRAM size (B)

-

Country of Origin

PHILIPPINES

(*) 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