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M48T129YSH Datasheet(PDF) 3 Page - STMicroelectronics |
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M48T129YSH Datasheet(HTML) 3 Page - STMicroelectronics |
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3 / 22 page  3/22 M48T129Y, M48T129V Figure 3. Block Diagram AI02583 LITHIUM CELL OSCILLATOR AND CLOCK CHAIN VPFD VCC VSS 32,768 Hz CRYSTAL VOLTAGE SENSE AND SWITCHING CIRCUITRY 16 x 8 TIMEKEEPER REGISTERS 131,056 x 8 SRAM ARRAY A0-A16 DQ0-DQ7 E W G POWER RST IRQ/FT cess. Insertion of the SNAPHAT housing after reflow prevents potential battery damage due to the high temperatures required for device surface- mounting. The SNAPHAT housing is keyed to pre- vent reverse insertion. The SNAPHAT battery package is shipped sepa- rately in plastic anti-static tubes or in Tape & Reel form. The part number is ”M4Txx-BR12SH1”. The 32 pin 600 mil DIP Hybrid houses a controller chip, SRAM, quartz crystal, and a long life lithium button cell in a single package. Figure 3 illustrates the static memory array and the quartz controlled clock oscillator. The clock loca- tions contain the century, year, month, date, day, hour, minute, and second in 24 hour BCD format. Corrections for 28, 29 (leap year), 30, and 31 day months are made automatically. The nine clock bytes (1FFFFh-1FFF9h and 1FFF1h) are not the actual clock counters, they are memory locations consisting of BiPORT ™ read/write memory cells within the static RAM array. The M48T129Y/V includes a clock control circuit which updates the clock bytes with current infor- mation once per second. The information can be accessed by the user in the same manner as any other location in the static memory array. Byte 1FFF8h is the clock control register. This byte con- trols user access to the clock information and also stores the clock calibration setting. Byte 1FFF7h contains the watchdog timer setting. The watchdog timer can generate either a reset or an interrupt, depending on the state of the Watch- dog Steering bit (WDS). Bytes 1FFF6h-1FFF2h in- clude bits that, when programmed, provide for clock alarm functionality. Alarms are activated when the register content matches the month, date, hours, minutes, and seconds of the clock registers. Byte 1FFF1h contains century informa- tion. Byte 1FFF0h contains additional flag informa- tion pertaining to the watchdog timer, the alarm condition and the battery status. The M48T129Y/V also has its own Power-Fail Detect circuit. This control circuitry constantly monitors the supply voltage for an out of tolerance condition. When VCC is out of tolerance, the circuit write protects the TIMEKEEPER register data and external SRAM, providing data security in the midst of un- predictable system operation. As VCC falls, the control circuitry automatically switches to the bat- tery, maintaining data and clock operation until valid power is restored. |
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