PCF8564A datasheet(51/86 Pages) NXP

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NXP Semiconductors

PCA2131

Nano-power highly accurate RTC with integrated quartz crystal for automotive applications

6. Clear STOP (register Control_1, STOP is logic 0).

7. Apply 80 clock pulses to CLKOUT.

8. Read hundredths registers to see the first change.

9. Apply 8096 clock pulses to CLKOUT (8096 + 80 = 8176 total pulses).

10.Read seconds registers to see the first change.

11.Apply the number of pulses needed for the current dither value.

12.Read the hundredths register to see subsequent changes.

13.Read the seconds register every 8192 pulses to see subsequent changes.

7.15 STOP bit function

The STOP bit stops the time from counting in both RTC mode and external clock test

mode. STOP must be set to unlock the time and date registers to set the time.

aaa-041575

OSCILLATOR

OSCILLATOR STOP

DETECTOR

setting the OS flag

div 4

32768 Hz

8192 Hz

stop

PRESCALER

RESET

100 Hz tick

1 Hz tick

CPR

Figure 22. CPR and STOP bit functional diagram

The stop signal blocks the 8.192 kHz clock from generating system clocks and freezes

the time. In this state, the prescaler can be cleared with the CPR command in the Resets

Remark: The CLKOUT output of clock frequencies is not affected.

The time circuits can then be set and do not increment until the STOP bit is released.

There is a slight chance that STOP is set during a carry over of multiple time registers,

which may have been executed incomplete. Therefore time must be set before clearing

STOP to maintain time integrity.

The stop acts on the 8.192 kHz signal. Because the I2C-bus or TS pin input is

asynchronous to the crystal oscillator, the accuracy of restarting the time circuits is

between zero and one 8.192 kHz cycle (see Figure 23).

aaa-004417

0 µs to 122 µs

8192 Hz

stop released

Figure 23. STOP release timing

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

PCA2131

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Product data sheet

Rev. 1.0 — 26 July 2021

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