PCF8523TSLASH1 datasheet(43/75 Pages) NXP

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PCF8523

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Product data sheet

Rev. 4 — 5 July 2012

43 of 74

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 causes the upper part of the prescaler (F2 to F14) to be held in reset and thus no

1 Hz ticks are generated. The time circuits can then be set and do not increment until the

STOP bit is released (see Figure 26).

STOP does 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 27).

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 45).

Fig 26. STOP bit

Fig 27. 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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