Obsolete

Product(s)

- Obsolete

Product(s)

Obsolete

Product(s)

- Obsolete

Product(s)

Clock operations

M48T59, M48T59Y, M48T59V

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3

Clock operations

3.1

Reading the clock

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 (1FF8h).

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 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.'

3.2

Setting the clock

Bit D7 of the Control register (1FF8h) 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 on page 13).

Resetting the WRITE Bit to a '0' then transfers the values of all time registers (1FF9h-

1FFFh) to the actual TIMEKEEPER counters and allows normal operation to resume. After

the WRITE Bit is reset, the next clock update will occur within approximately one second.

See the Application Note AN923, “TIMEKEEPER Rolling Into the 21st Century” for

information on Century Rollover.

Note:

Upon power-up following a power failure, both the WRITE Bit and the READ Bit will be reset

to '0.'

3.3

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 M48T59/Y/V in the DIP package is shipped from STMicroelectronics with the

STOP Bit set to a '1.' When reset to a '0,' the M48T59/Y/V oscillator starts within one

second.

Note:

It is not necessary to set the WRITE Bit when setting or resetting the FREQUENCY TEST

Bit (FT), the STOP Bit (ST) or the CENTURY ENABLE Bit (CEB).