●Summary
●The M41T256Y Serial TIMEKEEPER® SRAM is a low power 256Kbit static CMOS SRAM organized as 32K words by 8 bits. A built-in 32.768kHz oscillator (external crystal controlled) and 8 bytes of the SRAM (see Table 3 on page 18) are used for the clock/calendar function and are configured in binary coded decimal (BCD) format.
●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 M41T256Y 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 lithium button-cell supply when a power failure occurs. Functions available to the user include a non-volatile, time-of-day clock/calendar, and power-on reset. The eight clock address locations contain the year, month, date, day, hour, minute, second, and tenths/hundredths of seconds in 24-hour BCD format. Corrections for 28, 29 (leap year - valid until year 2100), 30 and 31 day months are made automatically. The first clock address location (7FF8h) stores the clock software calibration settings as well as the write clock bit.
●Features
●■ 5V operating voltage
●■ Serial interface supports extended I2C bus addressing (400kHz)
●■ Automatic switchover and deselect circuitry
●■ Power-fail deselect voltages:
● – M41T256Y: VCC = 4.5 V to 5.5V; VPFD = 4.2V < VPFD < 4.5V
●■ Counters for tenths/hundredths of seconds, seconds, minutes, hours, day, date, month, and year
●■ Programmable software clock calibration
●■ 32,752 bytes of general purpose RAM
●■ Microprocessor power-on reset
●■ Holds microprocessor in reset until supply voltage reaches stable operating level
●■ Automatic address-incrementing
●■ Tamper indication circuit with time-stamp
●■ Sleep mode function
●■ Available in ST’s 44-lead SNAPHAT® SOIC - mates with ST’s removable/replaceable SNAPHAT® battery/crystal top (ordered separately)
●■ RoHS compliant
● – Lead-free second level interconnect
