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M41ST85W ๋ฐ์ดํ„ฐ์‹œํŠธ(HTML) 4 Page - STMicroelectronics

๋ถ€ํ’ˆ๋ช… M41ST85W
์ƒ์„ธ๋‚ด์šฉ  3.0/3.3V I2C Combination Serial RTC, NVRAM Supervisor and Microprocessor Supervisor
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์ œ์กฐ์‚ฌ  STMICROELECTRONICS [STMicroelectronics]
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SUMMARY DESCRIPTION
The M41ST85W is a combination Serial Real-
Time Clock, Microprocessor Supervisor, and
NVRAM Supervisor. It is built in a low power
CMOS SRAM process and has a 64-byte memory
space with 44 bytes of NVRAM and 20 memory-
mapped RTC registers (see Table 2., page 14).
The RTC registers are configured in binary coded
decimal (BCD) format.
The M41ST85W combines a 400kHz I2C Serial
RTC with an Automatic Back-up Battery Switcho-
ver circuit for powering an external LPSRAM as
well as the internal RTC. When power begins to
fail, the switchover automatically connects to the
back-up battery to keep the RTC and external
LPSRAM alive in the absence of system power.
Access to the LPSRAM is also cut off via a chip-
enable gate function, thereby write-protecting the
memory. A programmable Watchdog and Power-
on Reset/Low Voltage Detect function are the key
elements in the Microprocessor Supervisor sec-
tion.
The
Real-Time
Clock
includes
a
built-in
32.768kHz oscillator (crystal-controlled), which
provides the time base for the timekeeping and
calendar functions. Eight of the 20 clock registers
provide the basic clock/calendar functions while
the other 12 bytes provide status/control for the
Alarm, Watchdog, and Squarewave functions.
RTC addresses and data are transferred serially
via the two-line, bi-directional I2C interface. The
built-in address register is incremented automati-
cally after each WRITE or READ data byte.
The M41ST85W has a built-in power sense circuit
which detects power failures and automatically
switches to the back-up battery when a power fail-
ure occurs. During an outage, the power to sustain
the SRAM and clock operations is typically sup-
plied by a small lithium button-cell battery as is the
case when using the SNAPHATยฎ package option.
Functions available to the user include a non-vol-
atile, time-of-day clock/calendar, Alarm interrupts,
Watchdog Timer, and programmable Squarewave
generator. Other features include a Power-on Re-
set as well as two additional debounce reset inputs
(RSTIN1 and RSTIN2) which can also generate an
output Reset (RST).
The eight registers for basic clock/calendar func-
tions 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 M41ST85W is offered in two 28-lead SOIC
packages. The 300mil SOH28 SNAPHAT IC pack-
age mates with STโ€™s SNAPHAT Battery/Crystal
top (ordered separately). SNAPHAT battery op-
tions include 48mAh and 120mAh. STโ€™s 300mil
SOX28 Embedded Crystal IC includes the 32KHz
crystal and is perfect for applications where a low
profile is a must.
The SOH28 SNAPHAT SOIC includes sockets
with gold plated contacts at both ends for direct
connection to the SNAPHAT top. The SNAPHAT
battery/crystal top is inserted atop the IC package
after the completion of the surface mount assem-
bly process which avoids potential battery and
crystal damage due to the high temperatures re-
quired for device surface-mounting. The unique
design allows the battery to be replaced, thus ex-
tending the life of the RTC and NVRAM indefinite-
ly.
The SNAPHAT top is keyed to prevent reverse in-
sertion. The SNAPHAT IC and SNAPHAT tops are
shipped separately. The ICs are available in plas-
tic anti-static tubes or in Tape & Reel form. The
SNAPHAT tops are shipped in plastic anti-static
tubes. The part numbers are M4T28-BR12SH1
(48mAh) and M4T32-BR12SH1 (120mAh). For
the
extended
temperature
requirement,
the
120mAh M4T32-BR12SH6 is available. For more
information, see Table 19., page 32.
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 SOX embedded crystal SOIC typically
requires a user-supplied battery for non-volatile
operation. Capacitor back-up can also be imple-
mented with this package.


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