SUMMARY DESCRIPTION
The M41T94 Serial TIMEKEEPER® SRAM is a low power, 512-bit static CMOS SRAM organized as 64 words by 8 bits. A built-in 32,768 Hz oscillator (external crystal controlled) and 8 bytes of the SRAM (see Table 10, page 17) 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 SUMMARY
■ 2.7 TO 5.5V OPERATING VOLTAGE
■ SERIAL PERIPHERAL INTERFACE (SPI)
■ 2.5 TO 5.5V OSCILLATOR OPERATING VOLTAGE
■ AUTOMATIC SWITCH-OVER and DESELECT CIRCUITRY
■ 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
■ COUNTERS FOR TENTHS/HUNDREDTHS OF SECONDS, SECONDS, MINUTES, HOURS, DAY, DATE, MONTH, YEAR, and CENTURY
■ 44 BYTES OF GENERAL PURPOSE RAM
■ PROGRAMMABLE ALARM and INTERRUPT FUNCTION (VALID EVEN DURING BATTERY BACK-UP MODE)
■ WATCHDOG TIMER
■ MICROPROCESSOR POWER-ON RESET
■ BATTERY LOW FLAG
■ LOW OPERATING CURRENT OF 2.0mA
■ ULTRA-LOW BATTERY SUPPLY CURRENT OF 500nA (MAX)
■ 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