M41T81S

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Serial real-time clock (RTC) with alarm

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Product overview

Description

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.

  • All 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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STMicroelectronics - M41T81S

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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.

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