PCF2127ATSLASH1 datasheet(31/80 Pages) NXP

31 / 80 page

PCF2127A_2

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Product data sheet

Rev. 02 — 7 May 2010

31 of 80

NXP Semiconductors

PCF2127A

Integrated RTC, TCXO and quartz crystal

After this read/write access is completed, the time circuit is released again and any

pending request to increment the time counters that occurred during the read/write access

is serviced. A maximum of 1 request can be stored; therefore, all accesses must be

completed within 1 second (see Figure 18).

As a consequence of this method, it is very important to make a read or write access in

one go, that is, setting or reading seconds through to years should be made in one single

access. Failing to comply with this method could result in the time becoming corrupted.

As an example, if the time (seconds through to hours) is set in one access and then in a

second access the date is set, it is possible that the time may increment between the two

accesses. A similar problem exists when reading. A roll over may occur between reads

thus giving the minutes from one moment and the hours from the next. Therefore it is

advised to read all time and date registers in one access.

Fig 17. Data flow of the time function

Fig 18. Access time for read/write operations

001aaf901

1 Hz tick

12_24 hour mode

WEEKDAY

SECONDS

MINUTES

HOURS

DAYS

LEAP YEAR

CALCULATION

MONTHS

YEARS

t < 1 s

013aaa215

SLAVE ADDRESS

DATA

STOP

DATA

START

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