PCF2129A Datasheet, PDF (42/68 Pages) NXP Semiconductors – Integrated RTC, TCXO and quartz crystal

NXP Semiconductors
PCF2129A
Integrated RTC, TCXO and quartz crystal
8.14 STOP bit function
The function of the STOP bit is to allow for accurate starting of the time circuits. STOP will
cause the upper part of the prescaler (F₉ to F₁₄) to be held in reset and thus no 1 Hz ticks
are generated. The time circuits can then be set and will not increment until the STOP bit
is released. STOP will not affect the CLKOUT signal but the output of the prescaler in the
range of 32 Hz to 1 Hz (see Figure 24).
The lower stages of the prescaler, F₀ to F₈, are not reset and because the I²C-bus and the
SPI-bus are asynchronous to the crystal oscillator, the accuracy of re-starting the time
circuits is between 0 and one 64 Hz cycle (0.484375 s and 0.500000 s), see Table 46 and
Figure 25.
Table 46. First increment of time circuits after stop release
Bit
STOP
Prescaler bits^[1]
F₀ to F₈ - F₉ to F₁₄
Clock is running normally
1 Hz tick
Time
hh:mm:ss
Comment
0
010000111-010100
12:45:12
prescaler counting normally
STOP bit is activated by user. F₀ to F₈ are not reset and values cannot be predicted externally
1
xxxxxxxxx-000000
12:45:12
prescaler is reset; time circuits are frozen
New time is set by user
1
xxxxxxxxx-000000
08:00:00
prescaler is reset; time circuits are frozen
STOP bit is released by user
0
xxxxxxxxx-000000
08:00:00
prescaler is now running
0
xxxxxxxxx-100000
08:00:00
0
xxxxxxxxx-100000
08:00:00
0
xxxxxxxxx-110000
08:00:00
:
:
:
0
111111111-111110
08:00:00
0
000000000-000001
08:00:01
0 to 1 transition of F14 increments the time circuits
0
100000000-000001
08:00:01
:
:
:
0
111111111-111111
08:00:01
0
000000000-000000
08:00:01
0
100000000-000000
:
:
:
0
111111111-111110
08:00:01
0
000000000-000001
08:00:02
0 to 1 transition of F14 increments the time circuits
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[1] F₀ is clocked at 32.768 kHz.
PCF2129A_1
Product data sheet
Rev. 01 — 13 January 2010
© NXP B.V. 2010. All rights reserved.
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