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M48T128V-85PM1 Datasheet(PDF) 11 Page - STMicroelectronics |
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M48T128V-85PM1 Datasheet(HTML) 11 Page - STMicroelectronics |
11 / 22 page 11/22 M48T128Y, M48T128V* CLOCK OPERATIONS Reading the Clock Updates to the TIMEKEEPER® registers should be halted before clock data is read to prevent reading data in transition. The BiPORT™ TIME- KEEPER cells in the RAM array are only data reg- isters and not the actual clock counters, so updating the registers can be halted without dis- turbing the clock itself. Updating is halted when a '1' is written to the READ Bit, D6 in the Control Register (1FFF8h). As long as a '1' remains in that position, updating is halted. After a halt is issued, the registers reflect the count; that is, the day, date, and time that were current at the moment the halt command was is- sued. All of the TIMEKEEPER registers are updat- ed simultaneously. A halt will not interrupt an update in progress. Updating is within a second af- ter the bit is reset to a '0.' Setting the Clock Bit D7 of the Control Register (1FFF8h) is the WRITE Bit. Setting the WRITE Bit to a '1,' like the READ Bit, halts updates to the TIMEKEEPER reg- isters. The user can then load them with the cor- rect day, date, and time data in 24 hour BCD format (see Table 5., page 11). Resetting the WRITE Bit to a '0' then transfers the values of all time registers 1FFFFh-1FFF9h to the actual TIME- KEEPER counters and allows normal operation to resume. After the WRITE Bit is reset, the next clock update will occur one second later. Stopping and Starting the Oscillator The oscillator may be stopped at any time. If the device is going to spend a significant amount of time on the shelf, the oscillator can be turned off to minimize current drain on the battery. The STOP Bit is located at Bit D7 within 1FFF9h. Setting it to a '1' stops the oscillator. The M48T128Y/V is shipped from STMicroelectronics with the STOP Bit set to a '1.' When reset to a '0,' the M48T128Y/ V oscillator starts after one second. Table 5. Register Map Keys: S = SIGN Bit R = READ Bit W = WRITE Bit ST = STOP Bit 0 = Must be set to '0' Z = '0' and are Read only Y = '1' or '0' Address Data Function/Range BCD Format D7 D6 D5 D4 D3 D2 D1 D0 1FFFFh 10 Years Year Year 00-99 1FFFEh 0 0 0 10 M Month Month 01-12 1FFFDh 0 0 10 Date Date Date 01-31 1FFFCh 0 FT 0 0 0 Day Day 01-07 1FFFBh 0 0 10 Hours Hours Hours 00-23 1FFFAh 0 10 Minutes Minutes Minutes 00-59 1FFF9h ST 10 Seconds Seconds Seconds 00-59 1FFF8h W R S Calibration Control |
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