pcf2127a NXP Semiconductors, pcf2127a Datasheet - Page 47

• Manufacturer Part Number: pcf2127a
• Description: Integrated Rtc, Tcxo And Quartz Crystal
• Manufacturer: NXP Semiconductors

NXP Semiconductors
PCF2127A_1
Product data sheet
8.13.1.2 Countdown timer interrupts
8.13.2 INT pulse shortening
The pulse generator for the minute/second interrupt operates from an internal 64 Hz clock
and generates a pulse of
The generation of interrupts from the countdown timer is controlled via the CDTIE bit
(register Control_2).
The interrupt may be generated as a pulsed signal at every countdown period or as a
permanently active signal which follows the status of the countdown timer flag CDTF. Bit
TI_TP is used to control this flag.
The pulse generator for the countdown timer interrupt also uses an internal clock, but this
time it is dependent on the selected source clock for the countdown timer and on the
countdown value n. As a consequence, the width of the interrupt pulse varies (see
Table
Table 54.
[1]
If the MSF or CDTF flag (register Control_2) is cleared before the end of the INT pulse,
then the INT pulse is shortened. This allows the source of a system interrupt to be cleared
immediately when it is serviced, i.e. the system does not have to wait for the completion of
the pulse before continuing; see
and bit CDTF can be found in
Source clock (Hz)
4096
64
1
1
Fig 27. INT example for SI and MI when TI_TP is logic 0
⁄
60
n = loaded countdown value. Timer stopped when n = 0.
54).
MSF when only MI enabled
INT when only MI enabled
In this example, bit TI_TP is logic 0 and the MSF flag is cleared after an interrupt.
INT operation (bit TI_TP = 1)
MSF when SI enable
INT when SI enable
seconds counter
minutes counter
Rev. 01 — 21 January 2010
1
⁄
64
seconds in duration.
Section
INT period (s)
n = 1
1
1
1
1
⁄
⁄
⁄
⁄
8192
128
64
64
58
Figure 28
[1]
59
8.11.6.
and
Integrated RTC, TCXO and quartz crystal
Figure
59
11
00
12
29. Instructions for clearing bit MSF
n > 1
1
1
1
1
⁄
⁄
⁄
⁄
4096
64
64
64
00
PCF2127A
01
© NXP B.V. 2010. All rights reserved.
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