M48T128V-70PM1 STMICROELECTRONICS [STMicroelectronics], M48T128V-70PM1 Datasheet - Page 11

• Manufacturer Part Number: M48T128V-70PM1
• Manufacturer: STMICROELECTRONICS [STMicroelectronics]

M48T128Y, M48T128V
3
3.1
3.2
3.3
Clock operations
Reading the clock
Updates to the TIMEKEEPER
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 (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 issued. All of the TIMEKEEPER registers are updated
simultaneously. 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 (1FFF8h) 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
Resetting the WRITE bit to a '0' then transfers the values of all time registers 1FFFFh-
1FFF9h to the actual TIMEKEEPER 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.
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Doc ID 5746 Rev 6
registers should be halted before clock data is read to
Table 5 on page
Clock operations
12).
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