M48T59 查看數據表（PDF） - STMicroelectronics

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M48T59

5.0 or 3.3V, 64 Kbit (8 Kbit x8) TIMEKEEPER® SRAM

STMicroelectronics 

M48T59, M48T59Y, M48T59V*

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 (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 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 (1FF8h) 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 12). Resetting the

WRITE Bit to a '0' then transfers the values of all

time registers (1FF9h-1FFFh) to the actual TIME-

KEEPER 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.'

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 sec-

ond.

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 EN-

ABLE Bit (CEB).

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