Description
The M41T94 is a serial real-time clock with 44 bytes of NVRAM and a RESET output. A built-in 32,768 Hz oscillator (external crystal controlled) and 8 bytes of the SRAM (see Table 4 on page 18) 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.

FEATUREs
• Counters for tenths/hundredths of seconds, seconds, minutes, hours, day, date, month, year, and century
• 32 KHz crystal oscillator integrating load capacitance (12.5 pF) providing exceptional oscillator stability and high crystal series resistance operation
• Serial peripheral interface (2 MHz SPI)
• Ultralow battery supply current of 500 nA (max)
• 2.7 to 5.5 V operating voltage
• 2.5 to 5.5 V oscillator operating voltage
• Battery low flag
• Automatic switchover and deselect circuitry
• 44 bytes of general purpose RAM
• Programmable alarm and interrupt function (valid even during battery backup mode)
• Accurate programmable watchdog timer (from 62.5 ms to 128 s)
• Microprocessor power-on reset
• Choice of power-fail deselect voltages (VCC = 2.7 to 5.5 V):
   – THS = VSS; 2.55 V  VPFD  2.70 V
   – THS = VCC; 4.20 V  VPFD  4.50 V
• 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
• RoHS compliant
   – Lead-free second level interconnect