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M48T35AV-10PC1E Datasheet(PDF) 11 Page - STMicroelectronics |
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M48T35AV-10PC1E Datasheet(HTML) 11 Page - STMicroelectronics |
11 / 25 page 11/25 M48T35AY, M48T35AV CLOCK OPERATIONS Reading the Clock Updates to the TIMEKEEPER® registers (see Ta- ble 5) should be halted before clock data is read to prevent reading data in transition. The BiPORT™ TIMEKEEPER cells in the RAM array are only data registers and not the actual clock counters, so updating the registers can be halted without disturbing the clock itself. Updating is halted when a '1' is written to the READ Bit, D6 in the Control Register 7FF8h. 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 the time that were current at the moment the halt command was is- sued. All of the TIMEKEEPER registers are updated si- multaneously. A halt will not interrupt an update in progress. Updating is within a second after the bit is reset to a '0.' Setting the Clock Bit D7 of the Control Register 7FF8h is the WRITE Bit. Setting the WRITE Bit to a '1,' like the READ Bit, halts updates to the TIMEKEEPER® registers. The user can then load them with the correct day, date, and time data in 24 hour BCD format (see Table 5). Resetting the WRITE Bit to a '0' then transfers the values of all time registers 7FF9h- 7FFFh to the actual TIMEKEEPER counters and allows normal operation to resume. The FT Bit and the bits marked as '0' in Table 5 must be written to '0' to allow for normal TIMEKEEPER and RAM op- eration. After the WRITE Bit is reset, the next clock update will occur within one second. See the Application Note AN923, “TIMEKEEPER® Rolling Into the 21st Century” for information on Century Rollover. 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 the MSB of the seconds register. Setting it to a '1' stops the oscillator. The M48T35AY/V is shipped from STMicroelectronics with the STOP Bit set to a '1.' When reset to a '0,' the M48T35AY/ V oscillator starts within 1 second. Table 5. Register Map Keys: S = SIGN Bit FT = FREQUENCY TEST Bit (Must be set to '0' upon power for normal operation) R = READ Bit W = WRITE Bit ST = STOP Bit 0 = Must be set to '0' CEB = Century Enable Bit CB = Century Bit Note: When CEB is set to '1,' CB will toggle from '0' to '1' or from '1' to '0' at the turn of the century (dependent upon the initial value set). When CEB is set to '0,' CB will not toggle. The WRITE Bit does not need to be set to write to CEB. Address Data Function/Range BCD Format D7 D6 D5 D4 D3 D2 D1 D0 7FFFh 10 Years Year Year 00-99 7FFEh 0 0 0 10 M. Month Month 01-12 7FFDh 0 0 10 Date Date Date 01-31 7FFCh 0 FT CEB CB 0 Day Century/Day 00-01/01-07 7FFBh 0 0 10 Hours Hours Hours 00-23 7FFAh 0 10 Minutes Minutes Minutes 00-59 7FF9h ST 10 Seconds Seconds Seconds 00-59 7FF8h W R S Calibration Control |
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