M41ST84W datasheet(4/31 Pages) STMICROELECTRONICS

4 / 31 page

M41ST84Y, M41ST84W

4/31

SUMMARY DESCRIPTION

The M41ST84Y/W Serial supervisory TIMEKEEP-

ER® 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 9, 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 two line, bi-directional I2C interface. The

built-in address register is incremented automati-

cally after each WRITE or READ data byte.

The M41ST84Y/W has a built-in power sense cir-

cuit which detects power failures and automatical-

ly 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 fail-

ure 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 M41ST84Y/W is supplied in a 28-lead SOIC

SNAPHAT® package (which integrates both crys-

tal and battery in a single SNAPHAT top) or a 16-

pin SOIC. The 28-pin, 330mil SOIC provides sock-

ets with gold plated contacts at both ends for direct

connection to a separate SNAPHAT housing con-

taining 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

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 28-pin 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 20, 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.

Figure 3. Logic Diagram

Note: 1. For SO16 package only.

Table 1. Signal Names

Note: 1. For SO16 package only.

AI03677

SCL

VCC

M41ST84Y

M41ST84W

VSS

SDA

RSTIN

IRQ/FT/OUT

SQW

WDI

PFI

RST

PFO

VBAT

(1)

XI (1)

Oscillator Input

XO (1)

Oscillator Output

IRQ/FT/OUT

Interrupt/Frequency Test/Out

Output (Open Drain)

PFI

Power Fail Input

PFO

Power Fail Output

RST

Reset Output (Open Drain)

RSTIN

Reset Input

SCL

Serial Clock Input

SDA

Serial Data Input/Output

SQW

Square Wave Output

WDI

Watchdog Input

VCC

Supply Voltage

VBAT

(1)

Battery Supply Voltage

VSS

Ground

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