Summary 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 19) are used for the clock/calendar function and are configured in binary 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.

Feature summary
■ Counters for tenths/hundredths of seconds, seconds, minutes, hours, day, date, month, year, and century
■ 32KHz crystal oscillator integrating load capacitance (12.5pF) providing exceptional oscillator stability and high crystal series resistance operation
■ Serial peripheral interface (2MHz SPI)
■ Ultra-low battery supply current of 500nA (max)
■ 2.7 to 5.5V operating voltage
■ 2.5 to 5.5V oscillator operating voltage
■ Battery low Flag
■ Automatic switch-over and deselect circuitry
■ 44 bytes of general purpose RAM
■ Programmable Alarm and interrupt function (valid even during battery back-up mode)
■ Accurate programmable Watchdog timer (from 62.5ms to 128s)
■ Microprocessor power-on reset
■ Choice of power-fail deselect voltages (VCC = 2.7 to 5.5V):
   – THS = VSS; 2.55V ≤VPFD ≤2.70V
   – THS = VCC; 4.20V ≤VPFD ≤4.50V
■ Packaging includes a 28-lead SOIC and SNAPHAT® TOP (to be ordered separately) or 16-lead SOIC
■ 28-lead SOIC package provides direct connection for a SNAPHAT TOP which contains the battery and crystal