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
32.768kHz oscillator (external crystal controlled)
and 8 bytes of the SRAM (see Table 3., page 13)
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 of 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
V
CC
M41ST84Y
M41ST84W
V
SS
SDA
RSTIN
IRQ/FT/OUT
SQW
WDI
PFI
RST
PFO
V
BAT
(1)
XI
(1)
XO
(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
V
CC
Supply Voltage
V
BAT
(1)
Battery Supply Voltage
V
SS
Ground
