M41ST95W datasheet(4/35 Pages) STMICROELECTRONICS

4 / 35 page

M41ST95Y*, M41ST95W

4/35

SUMMARY DESCRIPTION

The M41ST95Y/W Serial TIMEKEEPER® SRAM

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

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

oscillator (external crystal controlled) and 8 bytes

of the SRAM (see Table 4., page 16) 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 serial SPI interface. The built-in address reg-

ister is incremented automatically after each

WRITE or READ data byte. The M41ST95Y/W

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 op-

erations 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 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 M41ST95Y/W is supplied in a 28-lead SOIC

SNAPHAT® (MH) package (which integrates both

crystal 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 SNAPHAT SOIC and battery/crystal packag-

es are shipped separately in plastic anti-static

tubes or in Tape & Reel form. For the 28-lead SO-

IC, the battery/crystal package (e.g., SNAPHAT)

part number is “M4TXX-BR12SH” (see Table

20., page 33).

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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