PCF8523 datasheet(41/66 Pages) NXP

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PCF8523

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Product data sheet

Rev. 3 — 30 March 2011

41 of 66

NXP Semiconductors

PCF8523

Real-Time Clock (RTC) and calendar

8.10 STOP bit function

The STOP bit function allows the 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. The time circuits can then be set and will not increment

until the STOP bit is released (see Figure 25).

STOP will not affect the output of 32.768 kHz, 16.384 kHz or 8.192 kHz (see

Section 8.9.1.1).

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

interface is asynchronous to the crystal oscillator, the accuracy of re-starting the time

circuits will be between 0 and one 8.192 kHz cycle (see Figure 26).

The first increment of the time circuits is between 0.499878 s and 0.500000 s after stop is

released. The uncertainty is caused by the prescaler bits F0 and F1 not being reset (see

Table 43).

Fig 25. STOP bit

Fig 26. STOP bit release timing

013aaa336

OSC

OSC STOP

DETECTOR

F13

RES

F14

RES

512 Hz

16384 Hz

8192 Hz

1 Hz tick

stop

CLKOUT source

oscillator stop flag

001aaf912

8192 Hz

stop released

μs to 122 μs

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