Summary description

M41T81S

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Summary description

The M41T81S is a low power Serial RTC with a built-in 32.768kHz oscillator (external crystal

controlled). Eight bytes of the SRAM (see Table 2: Clock register map on page 15) 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

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 (MY), 300mil SOIC package

which includes an embedded 32kHz crystal.

The 18-pin, embedded crystal SOIC requires only a user-supplied battery to provide non-

volatile operation.

Figure 1.

Logic diagram

1.

For SO8 package only

SCL

VCC

M41T81S

VSS

SDA

IRQ/FT/OUT/SQW

VBAT

XI

(1)

XO

(1)

AI09160