M41ST84W datasheet(4/29 Pages) STMICROELECTRONICS

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M41ST84W

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SUMMARY DESCRIPTION

The M41ST84W Serial Real-Time Clock is built in

a low power CMOS SRAM process. It has a 64-

byte memory space with 44 bytes of NVRAM and

20 memory-mapped RTC registers (see Table

3., page 14). The RTC registers are configured in

binary coded decimal (BCD) format.

A built-in, low power 32.768kHz oscillator (external

crystal controlled) provides the time base for the

timekeeping and calendar functions.

The basic clock/calendar functions are handled by

the first eight RTC registers, while the other twelve

bytes provide status/control for the Alarm, Watch-

dog, and Square Wave functions.

Addresses and data are transferred serially via the

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

address register is incremented automatically af-

ter each WRITE or READ data byte.

The M41ST84W 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-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 M41ST84W is supplied in a 16-lead SOIC

package.

Figure 2. Logic Diagram

Table 1. Signal Names

AI03677

SCL

VCC

M41ST84W

VSS

SDA

RSTIN

IRQ/FT/OUT

SQW

WDI

PFI

RST

PFO

VBAT

Oscillator Input

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

Battery Supply Voltage

VSS

Ground

No Connect

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