PCF8564AUSLASH5GBSLASH1 datasheet(18/44 Pages) NXP

18 / 44 page

PCF8564A_1

Product data sheet

Rev. 1 — 8 October 2009

18 of 44

NXP Semiconductors

PCF8564A

Real time clock and calendar

7. Apply 64 clock pulses to CLKOUT.

8. Read time registers to see the second change.

Repeat 7 and 8 for additional increments.

8.10 STOP bit function

The function of the STOP bit is to allow for accurate starting of the time circuits. The STOP

bit function will cause the upper part of the prescaler (F2 to F14) to be held in reset and

thus no 1 Hz ticks will be generated (see Figure 9). The time circuits can then be set and

will not increment until the STOP bit is released (see Figure 10 and Table 26).

The STOP bit function will not affect the output of 32.768 kHz on CLKOUT, but will stop

the generation of 1.024 kHz, 32 Hz and 1 Hz.

The lower two stages of the prescaler (F0 and F1) are not reset and because the I2C-bus

is asynchronous to the crystal oscillator, the accuracy of re-starting the time circuits will be

between zero and one 8.192 kHz cycle (see Figure 10).

Fig 9.

STOP bit functional diagram

Fig 10. STOP bit release timing

013aaa089

OSC

OSC STOP

DETECTOR

F13

RES

F14

RES

1024 Hz

32 Hz

1 Hz tick

stop

CLKOUT source

reset

32768 Hz

1 Hz

001aaf912

8192 Hz

stop released

µs to 122 µs

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