m41t81 STMicroelectronics, m41t81 Datasheet - Page 5

• Manufacturer Part Number: m41t81
• Description: Serial Access Real-time Clock With Alarms
• Manufacturer: STMicroelectronics

M41T81
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
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
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
SDA
SCL
XO
XI
V
CC
M41T81
V
SS
V
BAT
Table 2: Clock register map on page
IRQ/FT/OUT/SQW
AI04613
Summary description
14) are used
2
C
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