Datasheet

M41T81 Description

Doc ID 7529 Rev 10 5/29

1 Description

The M41T81 is a low-power serial 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

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

Table 1. Signal names

XI Oscillator input

XO Oscillator output

IRQ

/OUT/FT/SQW Interrupt / output driver / frequency test / square wave (open drain)

SDA Serial data input/output

SCL Serial clock input

BAT

Battery supply voltage

Supply voltage

Ground

SCL

M41T81

SDA

IRQ/FT/OUT/SQW

BAT

AI04613