m41t94 STMicroelectronics, m41t94 Datasheet - Page 6

• Manufacturer Part Number: m41t94
• Description: Serial Real-time Clock With 44 Bytes Nvram And Reset
• Manufacturer: STMicroelectronics

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Caution:
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Description
The M41T94 is a serial real-time clock with 44 bytes of NVRAM and a RESET output. A
built-in 32,768Hz oscillator (external crystal controlled) and 8 bytes of the SRAM (see
Table 4 on page
coded decimal (BCD) format.
An additional 12 bytes of RAM provide status/control of Alarm, Watchdog and Square Wave
functions. Addresses and data are transferred serially via a serial SPI interface. The built-in
address register is incremented automatically after each WRITE or READ data byte. The
M41T94 has a built-in power sense circuit which detects power failures and automatically
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 failure 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 two additional debounced inputs
(RSTIN1 and RSTIN2) 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 ninth clock
address location controls user access to the clock information and also stores the clock
software calibration setting.
The M41T94 is supplied in either a 16-lead plastic SOIC (requiring user supplied crystal and
battery) or a 28-lead SOIC SNAPHAT
in a single SNAPHAT top). The 28-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 surface mount process.
Insertion of the SNAPHAT housing after reflow prevents potential battery and crystal
damage due to the high temperatures required for device surface-mounting. The SNAPHAT
housing is also keyed to prevent reverse insertion.
The SOIC and battery/crystal packages are shipped separately in plastic anti-static tubes or
in Tape & Reel form. For the 28-lead SOIC, the battery/crystal package (e.g., SNAPHAT)
part number is “M4TXX-BR12SH” (see
Do not place the SNAPHAT battery/crystal top in conductive foam, as this will drain the
lithium button-cell battery.
19) are used for the clock/calendar function and are configured in binary
®
Table 21 on page
package (which integrates both crystal and battery
38).