Datasheet

Description M41T81S
6/32 Doc ID 10773 Rev 7
1 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 I
2
C
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.
Figure 1. Logic diagram
1. For SO8 package only
SCL
V
CC
M41T81S
V
SS
SDA
IRQ/FT/OUT/SQW
V
BAT
XI
(1)
XO
(1)
AI09160