PCF2129AT datasheet(25/68 Pages) NXP

25 / 68 page

PCF2129A_1

Product data sheet

Rev. 01 — 13 January 2010

25 of 68

NXP Semiconductors

PCF2129A

Integrated RTC, TCXO and quartz crystal

8.8.8 Setting and reading the time

Figure 13 shows the data flow and data dependencies starting from the 1 Hz clock tick.

During read/write operations, the time counting circuits (memory locations 03h through

09h) are blocked.

This prevents

• Faulty reading of the clock and calendar during a carry condition

• Incrementing the time registers during the read cycle

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 14).

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.

Fig 13. Data flow of the time function

Fig 14. 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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