PCF2123U/5GA/1 View Datasheet(PDF) - NXP Semiconductors.
Part Name
Description
MFG CO.
'PCF2123U/5GA/1' PDF : 63 Pages View PDF
NXP Semiconductors
PCF2123
SPI Real time clock/calendar
8.11 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. The time circuits can then be set and will not
increment until the STOP bit is released (see Figure 22 and Table 41).
The STOP bit function will not affect the output of 32.768 kHz, 16.384 kHz, or 8.192 kHz
(see Section 8.8).
OSCILLATOR STOP
DETECTOR
oscillator stop flag
OSCILLATOR
F0
F1
F2
RESET
F13
RESET
F14
RESET
1 Hz tick
stop
1 Hz
1024 Hz
Fig 21. STOP bit functional diagram
8192 Hz
16384 Hz
CLKOUT source
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The lower two stages of the prescaler (F0 and F1) are not reset and because the SPI-bus
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 22).
8192 Hz
stop released
Fig 22. STOP bit release timing
0 μs to 122 μs
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The first increment of the time circuits is between 0.499878 s and 0.500000 s after STOP
bit is released. The uncertainty is caused by the prescaler bits F0 and F1 not being reset
(see Table 41).
PCF2123
Product data sheet
All information provided in this document is subject to legal disclaimers.
Rev. 6 — 15 July 2013
© NXP B.V. 2013. All rights reserved.
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