M41ST85YMX datasheet(4/34 Pages) STMICROELECTRONICS

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M41ST85Y, M41ST85W

4/34

SUMMARY DESCRIPTION

The M41ST85Y/W Serial TIMEKEEPER®/Con-

troller SRAM is a low power 512-bit, static CMOS

SRAM organized as 64 words by 8 bits. A built-in

32.768 kHz oscillator (external crystal controlled)

and 8 bytes of the SRAM (see Table 2., page 14)

are used for the clock/calendar function and are

configured in binary 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 two line, bi-directional I2C interface. The

built-in address register is incremented automati-

cally after each WRITE or READ data byte. The

M41ST85Y/W has a built-in power sense circuit

which detects power failures and automatically

switches to the battery supply when a power fail-

ure occurs. The energy needed to sustain the

SRAM and clock operations can be supplied by a

small lithium button-cell supply when a power fail-

ure occurs.

Functions available to the user include a non-vol-

atile, 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 loca-

tions 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 M41ST85Y/W is supplied in a 28-lead SOIC

SNAPHAT® package (which integrates both crys-

tal and battery in a single SNAPHAT top) or a 28-

pin, 300mil SOIC package (MX) which includes an

embedded 32kHz crystal.

The 28-pin, 330mil SOIC provides sockets with

gold plated contacts at both ends for direct con-

nection to a separate SNAPHAT housing contain-

ing the battery and crystal. The unique design

allows the SNAPHAT battery/crystal package to

be mounted on top of the SOIC package after 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

“M4TXX-BR12SH”

(see

Table

19., page 32).

Caution: Do not place the SNAPHAT battery/crys-

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

ium button-cell battery.

The 300mil, embedded crystal SOIC requires only

a user-supplied battery to provide non-volatile op-

eration.

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