M41T81
Summary description
1
Summary description
The M41T81 is a low power Serial RTC with a built-in 32.768kHz oscillator (external crystal
controlled). Eight bytes of the SRAM (see
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, bi-directional I
2
C
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.
Figure 1.
Logic diagram
V
CC
V
BAT
XI
XO
M41T81
SCL
SDA
IRQ/FT/OUT/SQW
V
SS
AI04613
5/30
STMICROELECTRONICS [ STMICROELECTRONICS ]
