Description
The M41ST87Y/W secure serial RTC and NVRAM supervisor is a low power 1280-bit, static CMOS SRAM organized as 160 bytes by 8 bits. A built-in 32.768 kHz oscillator (internal crystal-controlled) and 8 bytes of the SRAM (see Table 7 ) are used for the clock/calendar function and are configured in binary coded decimal (BCD) format.
An additional 11 bytes of RAM provide calibration, status/control of alarm, watchdog, tamper, and square wave functions. 8 bytes of ROM and finally 128 bytes of user RAM are also provided. Addresses and data are transferred serially via a two line, bidirectional I2C interface. The built-in address register is incremented automatically after each WRITE or READ data byte. The M41ST87Y/W 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.
Features
â 5.0, 3.3, or 3.0 V operation
â 400 kHz I2C bus
â NVRAM supervisor to non-volatize external LPSRAM
â 2.5 to 5.5 V oscillator operating voltage
â Automatic switchover and deselect circuitry
â Choice of power-fail deselect voltages
â M41ST87Y:
THS = 1: VPFDâ 4.63 V; VCC = 4.75 to 5.5 V
THS = 0: VPFDâ 4.37 V; VCC = 4.5 to 5.5 V
â M41ST87W:
THS = 1: VPFD â 2.9 V; VCC = 3.0 to 3.6 V
THS = 0: VPFD â 2.63 V; VCC = 2.7 to 3.6 V
â Two independent power-fail comparators
(1.25 V reference)
â Counters for tenths/hundredths of seconds, seconds, minutes, hours, day, date, month, year, and century
â 128 bytes of clearable, general purpose NVRAM
â Programmable alarm and interrupt function
(valid even during battery backup mode)
â Programmable watchdog timer
â Unique electronic serial number (8-byte)
â 32 kHz frequency output available upon power on
â Microprocessor power-on reset output
â Battery low flag
â Ultra-low battery supply current of 500 nA (typ)
Security features
â Tamper indication circuits with timestamp and RAM clear
â LPSRAM clear function (TPCLR)
â Packaging includes a 28-lead, embedded crystal SOIC and a 20-lead SSOP
â Oscillator stop detection
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