M41T81 datasheet(1/29 Pages) STMICROELECTRONICS

Part #	M41T81

Description	Serial access real-time clock with alarm

PDF	29 Pages

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Manufacturer	STMICROELECTRONICS [STMicroelectronics]

Direct Link	http://www.st.com

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This is information on a product in full production.

February 2014

DocID007529 Rev 11

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M41T81

Serial access real-time clock with alarm

Datasheet

- production data

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

Description

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.

8

1

SO8

8-pin SOIC

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