M41ST87Y datasheet(5/42 Pages) STMICROELECTRONICS

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M41ST87Y, M41ST87W

SUMMARY DESCRIPTION

The M41ST87Y/W Serial TIMEKEEPER®/Con-

troller SRAM is a low power 1280-bit, static CMOS

SRAM organized as 160 bytes by 8 bits. A built-in

32.768 kHz oscillator (internal crystal-controlled)

and 8 bytes of the SRAM (see Table 7., page 25)

are used for the clock/calendar function and are

configured in binary coded decimal (BCD) format.

An additional 11 bytes of RAM provide calibration,

status/control of Alarm, Watchdog, Tamper, and

Square Wave functions. 8 bytes of ROM and final-

ly 128 bytes of User RAM are also provided. Ad-

dresses and data are transferred serially via a two

line, bi-directional I2C interface. The built-in ad-

dress register is incremented automatically after

each WRITE or READ data byte. The M41ST87Y/

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-vol-

atile, time-of-day clock/calendar, Alarm interrupts,

Tamper Detection, Watchdog Timer, and pro-

grammable Square Wave output. Other features

include a Power-On Reset as well as two addition-

al 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 for-

mat. Corrections for 28, 29 (leap year), 30 and 31

day months are made automatically.

Security Features

Two fully independent Tamper Detection Inputs al-

low monitoring of multiple locations within the sys-

tem. Programmable bits provide both, “Normally

Open” and “Normally Closed” switch monitoring.

Time Stamping of the tamper event is automatical-

ly provided. There is also an option allowing data

stored in either internal memory (128 bytes), and/

or external memory to be cleared, protecting sen-

sitive information in the event tampering occurs.

By embedding the 32kHz crystal in the package,

the clock is completely isolated from external tam-

pering. An Oscillator Fail Bit (OF) is also provided

to ensure correct operation of the oscillator.

The M41ST87Y/W is supplied in a 28-pin, 300mil

SOIC package (MX) which includes an embedded

32kHz crystal.

The SOIC package is shipped in plastic anti-static

tubes or in Tape & Reel form.

The 300mil, embedded crystal SOIC requires only

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

eration.

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