M41T81

The M41T81 Serial Access TIMEKEEPER® SRAM is a low power Serial RTC with a built-in 32.768 KHz oscillator (external crystal controlled). Eight bytes of the SRAM (see Table 10, page 16)M41T81 are used for the clock/calendar function and are configured in binary coded decimal (BCD) format. An additional 12 bytes of SRAM 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 M41T81 is incremented automatically after each WRITE or READ data byte.

The M41T81 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 asmall lithium button supply when a power failure occurs. Functions of M41T81 available to the user include a non-volatile, time-of-day clock/calendar, Alarm interrupts, Watchdog Timer and programmable Square Wave output. The eight clock address locations of M41T81 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 M41T81 is supplied in either an 8-pin SOIC or an 18-pin (MY) or 28-pin (MX), 300mil SOIC package which includes an embedded 32kHz crystal. The 8-pin and 28-pin, embedded crystal SOIC M41T81 requires only a user-supplied battery to provide nonvolatile operation.