PCF2131 datasheet(32/86 Pages) NXP

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NXP Semiconductors

PCF2131

Nano-power highly accurate RTC with integrated quartz crystal

aaa-009580

SECONDS

100 Hz tick

MINUTES

HOURS

12_24

DAYS

WEEKDAY

LEAP YEAR

CALCULATION

MONTHS

YEARS

100TH_SECOND

100TH

1 Hz tick

Figure 13. Data flow for the time function

Write access requires setting the STOP bit. The flow for accurately setting the time in

RTC mode is:

• start an I2C access at register control_1

• set STOP bit

• set CPR (register SR_RESET, CPR is logic 1)

• address counter rolls over to address 06h

• set time (100th seconds, seconds to years)

• end I2C access

• wait for external time reference to indicate that time counting should start

• start an I2C access at register control_1

• clear STOP bit (time starts counting from now)

• end I2C access

The first increment of the time circuits is between 0 s and 122 ms after STOP is released.

See description for STOP bit in Section 7.15

During read operations, the time counting circuits (memory locations 06h through 0Dh)

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 access is completed, the time circuit is released again. Any pending

request to increment the time counters that occurred during the read access is serviced.

As a consequence of this method, it is very important to make a read access in one go.

That is, 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.

PCF2131

All information provided in this document is subject to legal disclaimers.

Product data sheet

Rev. 1.1 — 15 October 2021

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