M41T256YMT7F datasheet(4/27 Pages) STMICROELECTRONICS

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M41T256Y

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SUMMARY DESCRIPTION

The M41T256Y Serial TIMEKEEPER® SRAM is a

low power 256 Kbit static CMOS SRAM organized

as 32K words by 8 bits. A built-in 32.768kHz oscil-

lator (external crystal controlled) and 8 bytes of the

SRAM (see Table 3., page 14) are used for the

clock/calendar function and are configured in bina-

ry coded decimal (BCD) format.

Addresses and data are transferred serially via a

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

address register is incremented automatically af-

ter each WRITE or READ data byte.

The M41T256Y 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

lithium button-cell supply when a power failure oc-

curs. Functions available to the user include a

non-volatile, time-of-day clock/calendar, and Pow-

er-on Reset. The eight clock address locations

contain the year, month, date, day, hour, minute,

second, and tenths/hundredths of seconds in 24-

hour BCD format. Corrections for 28, 29 (leap year

- valid until year 2100), 30 and 31 day months are

made automatically. The first clock address loca-

tion (7FF8h) stores the clock software calibration

settings as well as the Write Clock Bit.

The M41T256Y is supplied in a 44-lead SOIC

SNAPHAT® package (MH - which integrates both

crystal and battery in a single SNAPHAT top) or a

44-pin “hatless” SOIC (MT). The 44-pin, 330mil

SOIC provides sockets with gold-plated contacts

at both ends for direct connection to a separate

SNAPHAT housing containing 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 sur-

face-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 44-pin

SOIC and crystal/battery packages are shipped

separately in plastic, anti-static tubes or in Tape &

Reel form. For the 44-lead SOIC, the battery/crys-

tal package (e.g., SNAPHAT) part number is

“M4Txx-BR12SH” (see Table 15., page 25).

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 44-pin SNAPHAT (MT) package only.

Table 1. Signal Names

Note: 1. For 44-pin SNAPHAT (MT) package only.

AI04754b

SCL

VCC

M41T256Y

VSS

SDA

RST

VBAT

(1)

XI(1)

Oscillator Input

XO(1)

Oscillator Output

Frequency Test (Open drain)

RST

Reset Output (Open drain)

SCL

Serial Clock Input

SDA

Serial Data Input/Output

VCC

Supply Voltage

VBAT

(1)

Battery Supply Voltage

VSS

Ground

Tamper Input

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