PCF2129AT datasheet(29/68 Pages) NXP

29 / 68 page

PCF2129A_1

Product data sheet

Rev. 01 — 13 January 2010

29 of 68

NXP Semiconductors

PCF2129A

Integrated RTC, TCXO and quartz crystal

8.10 Timer functions

The PCF2129A has a watchdog timer function. The timer can be selected by using the

control bit WD_CD in the register Watchdg_tim_ctl.

The watchdog timer has four selectable source clocks. It can be used to detect a

microprocessor 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

[1]

Default value.

[2]

When writing to the register this bit has always to be set logic 0.

8.10.2 Register Watchdg_tim_val

Table 30.

Watchdg_tim_ctl - watchdog timer control register (address 10h) bit description

Bit

Symbol

Value

Description

WD_CD

0[1]

watchdog timer disabled

watchdog timer enabled;

the interrupt pin INT is activated when timed out

0[2]

unused

5TI_TP

0[1]

the interrupt pin INT is configured to generate a

permanent active signal when MSF (register Control_2)

is set

the interrupt pin INT is configured to generate a pulsed

signal when MSF flag is set (see Figure 19)

4to2

unused

1 to 0 TF[1:0]

timer source clock for watchdog timer

4.096 kHz

64 Hz

1 Hz

11[1]

⁄

60 Hz

Table 31.

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

countdown period in seconds:

where n is the countdown value

CountdownPeriod

SourceClockFrequency

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