M41ST84W datasheet(6/34 Pages) STMICROELECTRONICS

6 / 34 page

Description

M41ST84W

6/34

Description

The M41ST84W serial real-time clock is built in a low power CMOS SRAM process. It has a

64-byte memory space with 44 bytes of NVRAM and 20 memory-mapped RTC registers

(see Table 3 on page 18). The RTC registers are configured in binary coded decimal (BCD)

format.

A built-in, low power 32.768 kHz oscillator (external crystal controlled) provides the time

base for the timekeeping and calendar functions.

The basic clock/calendar functions are handled by the first eight RTC registers, while the

other twelve bytes provide status/control for the alarm, watchdog, and square wave

functions.

Addresses and data are transferred serially via the two line, bidirectional I2C interface. The

built-in address register is incremented automatically after each WRITE or READ data byte.

The M41ST84W 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-

cell 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. Other features include a power-on reset as well as an additional input

(RSTIN) which can also generate an output reset (RST). 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 M41ST84W is supplied in a 16-lead SOIC package.

M41ST84W Datasheet(PDF) 6 Page - STMicroelectronics