M41T81SM6FT datasheet(4/29 Pages) STMICROELECTRONICS

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M41T81S

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SUMMARY DESCRIPTION

The M41T81S Serial Access TIMEKEEPER®

SRAM is a low power Serial RTC with a built-in

32.768kHz oscillator (external crystal controlled).

Eight bytes of the SRAM (see Table 2., page 12)

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 se-

rially via a two line, bi-directional I2C interface. The

built-in address register is incremented automati-

cally 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 fail-

ure occurs. The energy needed to sustain the

clock operations can be supplied by a small lithium

button supply when a power failure occurs. Func-

tions 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 sec-

ond 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 (MY), 300mil SOIC package which in-

cludes an embedded 32kHz crystal.

The 18-pin, embedded crystal SOIC requires only

a user-supplied battery to provide non-volatile op-

eration.

Figure 2. Logic Diagram

Note: 1. For SO8 package only.

Table 1. Signal Names

Note: 1. For SO8 package only.

2. NC and NF pins should be tied to VSS.

SCL

VCC

M41T81S

VSS

SDA

IRQ/FT/OUT/SQW

VBAT

(1)

AI09160

XI(1)

Oscillator Input

XO(1)

Oscillator Output

IRQ/OUT/

FT/SQW

Interrupt / Output Driver / Frequency

Test / Square Wave (Open Drain)

SDA

Serial Data Input/Output

SCL

Serial Clock Input

VBAT

Battery Supply Voltage

VCC

Supply Voltage

VSS

Ground

NC(2)

No Connect

NF(2)

No Function

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