pcf2127a NXP Semiconductors, pcf2127a Datasheet - Page 36

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

NXP Semiconductors
PCF2127A_1
Product data sheet
8.11.2 Register Watchdg_tim_val
8.11.3 Watchdog timer function
Table 35.
Table 36.
The watchdog timer function is controlled by the WD_CD[1:0] bits of the register
Watchdg_tim_ctl (see
The two bits TF[1:0] in register Watchdg_tim_ctl determine one of the four source clock
frequencies for the watchdog timer: 4.096 kHz, 64 Hz, 1 Hz, or
When the watchdog timer function is enabled, the 8 bit timer in register Watchdg_tim_val
(see
The watchdog timer counts down from the software programmed 8 bit binary value n in
register Watchdg_tim_val. When the counter reaches 1 the watchdog timer flag WDTF is
set logic 1.
In the case that WDTF is logic 1:
The counter does not automatically reload.
When WD_CD[1:0] = 10 or WD_CD[1:0] = 11 and the microcontroller unit (MCU) loads a
watchdog timer value n:
Loading the counter with 0 will:
Bit
7 to 0 WATCHDG_TIM_VAL[7:0]
TF[1:0] Timer source
00
01
10
11
•
•
•
•
•
•
•
•
if WD_CD[1:0] = 10 an interrupt will be generated
if WD_CD[1:0] = 11 a reset will be generated
the flag WDTF is reset
INT or RST is cleared
the watchdog timer starts again
reset the flag WDTF
clear INT or RST
stop the watchdog timer
Table
Symbol
clock frequency
4.096
64
1
1
⁄
60
Watchdg_tim_val - watchdog timer value register (address 11h) bit description
Programmable watchdog or countdown timer
35) determines the watchdog timer period.
Rev. 01 — 21 January 2010
Table
34).
Units
kHz
Hz
Hz
Hz
Value
00 to FF countdown period in seconds:
Minimum timer
period (n = 1)
244
15.625
1
60
Description
where n is the countdown value
CountdownPeriod
Integrated RTC, TCXO and quartz crystal
Units
μs
ms
s
s
=
Maximum timer
period (n = 255)
62.256
3.984
255
15300
1
-------------------------------------------------------------- -
SourceClockFrequency
⁄
60
PCF2127A
Hz (see
© NXP B.V. 2010. All rights reserved.
n
Table
36).
Units
ms
s
s
s
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