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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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CAD/EDA Symbols, Footprints and Models

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

Part Number
Order from Distributors
Order from ST
Marketing Status
ECCN (US)
ECCN (EU)
Packing Type
Package
Temperature (°C) Budgetary Price (US$)*/Qty
More info
min
max
M41T81SM6F Available at 9 distributors

Distributor availability ofM41T81SM6F

Distributor Name
Region Stock Min. Order Third party link
DIGIKEY WORLDWIDE 917 1 Order Now
COMPEL EUROPE 843 1 Order Now
RS COMPONENTS EUROPE 4370 5 Order Now
AVNET AMERICA 28680 0 Order Now
FUTURE WORLDWIDE 296 1 Order Now
ARROW EUROPE 2500 0 Order Now
ARROW AMERICA 7550 1 Order Now
MOUSER WORLDWIDE 9949 1 Order Now
RUTRONIK EUROPE 2500 2500 Order Now

Distributor reported inventory date: 2020-10-21

Distributor Name

DIGIKEY

Stock

917

Min.Order

1

Region

WORLDWIDE Order Now

COMPEL

Stock

843

Min.Order

1

Region

EUROPE Order Now

RS COMPONENTS

Stock

4370

Min.Order

5

Region

EUROPE Order Now

AVNET

Stock

28680

Min.Order

0

Region

AMERICA Order Now

FUTURE

Stock

296

Min.Order

1

Region

WORLDWIDE Order Now

ARROW

Stock

2500

Min.Order

0

Region

EUROPE Order Now

ARROW

Stock

7550

Min.Order

1

Region

AMERICA Order Now

MOUSER

Stock

9949

Min.Order

1

Region

WORLDWIDE Order Now

RUTRONIK

Stock

2500

Min.Order

2500

Region

EUROPE Order Now

Distributor reported inventory date: 2020-10-21

Free Sample Buy Direct
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 5 distributors

Distributor availability ofM41T81SMY6F

Distributor Name
Region Stock Min. Order Third party link
DIGIKEY WORLDWIDE 2015 1 Order Now
AVNET AMERICA 5000 0 Order Now
FUTURE WORLDWIDE 2000 1000 Order Now
Newark Element14 AMERICA 852 0 Order Now
MOUSER WORLDWIDE 2123 1 Order Now

Distributor reported inventory date: 2020-10-21

Distributor Name

DIGIKEY

Stock

2015

Min.Order

1

Region

WORLDWIDE Order Now

AVNET

Stock

5000

Min.Order

0

Region

AMERICA 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

2123

Min.Order

1

Region

WORLDWIDE Order Now

Distributor reported inventory date: 2020-10-21

Free Sample Buy Direct
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 917 1 Order Now
COMPEL EUROPE 843 1 Order Now
RS COMPONENTS EUROPE 4370 5 Order Now
AVNET AMERICA 28680 0 Order Now
FUTURE WORLDWIDE 296 1 Order Now
ARROW EUROPE 2500 0 Order Now
ARROW AMERICA 7550 1 Order Now
MOUSER WORLDWIDE 9949 1 Order Now
RUTRONIK EUROPE 2500 2500 Order Now

Distributor reported inventory date: 2020-10-21

Distributor Name

DIGIKEY

Stock

917

Min.Order

1

Region

WORLDWIDE Order Now

COMPEL

Stock

843

Min.Order

1

Region

EUROPE Order Now

RS COMPONENTS

Stock

4370

Min.Order

5

Region

EUROPE Order Now

AVNET

Stock

28680

Min.Order

0

Region

AMERICA Order Now

FUTURE

Stock

296

Min.Order

1

Region

WORLDWIDE Order Now

ARROW

Stock

2500

Min.Order

0

Region

EUROPE Order Now

ARROW

Stock

7550

Min.Order

1

Region

AMERICA Order Now

MOUSER

Stock

9949

Min.Order

1

Region

WORLDWIDE Order Now

RUTRONIK

Stock

2500

Min.Order

2500

Region

EUROPE Order Now

Distributor reported inventory date: 2020-10-21

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 2015 1 Order Now
AVNET AMERICA 5000 0 Order Now
FUTURE WORLDWIDE 2000 1000 Order Now
Newark Element14 AMERICA 852 0 Order Now
MOUSER WORLDWIDE 2123 1 Order Now

Distributor reported inventory date: 2020-10-21

Distributor Name

DIGIKEY

Stock

2015

Min.Order

1

Region

WORLDWIDE Order Now

AVNET

Stock

5000

Min.Order

0

Region

AMERICA 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

2123

Min.Order

1

Region

WORLDWIDE Order Now

Distributor reported inventory date: 2020-10-21

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