NXP Semiconductors
PCF2129T
Accurate RTC with integrated quartz crystal for industrial
8.10 Timer functions
The PCF2129T has a watchdog timer function. The timer can be switched on and off by
using the control bit WD_CD in the register Watchdg_tim_ctl.
The watchdog timer has four selectable source clocks. It can, for example, be used to
detect a microcontroller with interrupt and reset capability which is out of control (see
Section 8.10.3)
To control the timer function and timer output, the registers Control_2, Watchdg_tim_ctl,
and Watchdg_tim_val are used.
8.10.1 Register Watchdg_tim_ctl
Table 31. Watchdg_tim_ctl - watchdog timer control register (address 10h) bit description
Bit Symbol
Value Description
7
WD_CD
0[1]
watchdog timer disabled
1
watchdog timer enabled;
the interrupt pin INT is activated when timed out
6
T
0[2]
unused
5
TI_TP
0[1]
the interrupt pin INT is configured to generate a
permanent active signal when MSF (register Control_2)
is set
1
the interrupt pin INT is configured to generate a pulsed
signal when MSF flag is set (see Figure 19)
4 to 2 -
-
unused
1 to 0 TF[1:0]
timer source clock for watchdog timer
00
4.096 kHz
01
64 Hz
10
1 Hz
11[1]
1⁄60 Hz
[1] Default value.
[2] When writing to the register this bit always has to be set logic 0.
8.10.2 Register Watchdg_tim_val
Table 32. Watchdg_tim_val - watchdog timer value register (address 11h) bit description
Bit Symbol
Value Description
7 to 0 WATCHDG_TIM_VAL[7:0] 00 to FF timer period in seconds:
TimerPeriod = -------------------------------n-------------------------------
SourceClockFrequency
where n is the timer value
PCF2129T
Product data sheet
All information provided in this document is subject to legal disclaimers.
Rev. 3 — 12 February 2013
© NXP B.V. 2013. All rights reserved.
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