M41T94 datasheet(4/31 Pages) STMICROELECTRONICS

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M41T94

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SUMMARY DESCRIPTION

The M41T94 Serial TIMEKEEPER® SRAM is a

low power, 512-bit static CMOS SRAM organized

as 64 words by 8 bits. A built-in 32,768 Hz oscilla-

tor (external crystal controlled) and 8 bytes of the

SRAM (see Table 10, page 17) are used for the

clock/calendar function and are configured in bina-

ry coded decimal (BCD) format.

An additional 12 bytes of RAM provide status/con-

trol of Alarm, Watchdog and Square Wave func-

tions. Addresses and data are transferred serially

via a serial SPI interface. The built-in address reg-

ister is incremented automatically after each

WRITE or READ data byte. The M41T94 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 sup-

ply when a power failure occurs. Functions avail-

able 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 two

additional

debounced

inputs

(RSTIN1

and

RSTIN2) 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 ninth clock address loca-

tion controls user access to the clock information

and also stores the clock software calibration set-

ting.

The M41T94 is supplied in either a 16-lead plastic

SOIC (requiring user supplied crystal and battery)

or a 28-lead SOIC SNAPHAT® package (which in-

tegrates both crystal and battery in a single

SNAPHAT top). The 28-pin, 330mil SOIC provides

sockets with gold plated contacts at both ends for

direct connection to a separate SNAPHAT hous-

ing containing the battery and crystal. The unique

design allows the SNAPHAT battery/crystal pack-

age to be mounted on top of the SOIC package af-

ter the completion of the surface mount process.

Insertion of the SNAPHAT housing after reflow

prevents potential battery and crystal damage due

to the high temperatures required for device sur-

face-mounting. The SNAPHAT housing is also

keyed to prevent reverse insertion.

The SOIC and battery/crystal packages are

shipped separately in plastic anti-static tubes or in

Tape & Reel form. For the 28-lead SOIC, the bat-

tery/crystal package (e.g., SNAPHAT) part num-

ber is “M4TXX-BR12SH” (see Table 21, page 29).

Caution: Do not place the SNAPHAT battery/crys-

tal top in conductive foam, as this will drain the lith-

ium button-cell battery.

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