SUMMARY DESCRIPTION
The M41ST84Y/W Serial supervisory TIMEKEEPER® SRAM is a low power 512-bit static CMOS SRAM organized as 64 words by 8 bits. A built-in 32.768 kHz oscillator (external crystal controlled) and 8 bytes of the SRAM (see Table 9, page 16) 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 two line, bi-directional I2C interface. The built-in address register is incremented automatically after each WRITE or READ data byte.
The M41ST84Y/W has a built-in power sense circuit 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 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 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.

FEATURES SUMMARY
■ 5.0 OR 3.0V OPERATING VOLTAGE
■ SERIAL INTERFACE SUPPORTS I2C BUS (400 KHz)
■ OPTIMIZED FOR MINIMAL INTERCONNECT TO MCU
■ 2.5 TO 5.5V OSCILLATOR OPERATING VOLTAGE
■ AUTOMATIC SWITCH-OVER and DESELECT CIRCUITRY
■ CHOICE OF POWER-FAIL DESELECT VOLTAGES:
   – M41ST84Y:
      VCC = 4.5 to 5.5V;
      4.20V ≤ VPFD ≤ 4.50V
   – M41ST84W:
      VCC = 2.7 to 3.6V;
      2.55V ≤ VPFD ≤ 2.70V
■ 1.25V REFERENCE (for PFI/PFO)
■ 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
■ ULTRA-LOW BATTERY SUPPLY CURRENT OF 500 nA (max)
■ OPTIONAL PACKAGING INCLUDES A 28-LEAD SOIC and SNAPHAT® TOP (to be ordered separately)
■ SNAPHAT PACKAGE PROVIDES DIRECT CONNECTION FOR A SNAPHAT TOP, WHICH CONTAINS THE BATTERY and CRYSTAL