PCF2127ATSLASH1 datasheet(35/80 Pages) NXP

35 / 80 page

PCF2127A_2

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Product data sheet

Rev. 02 — 7 May 2010

35 of 80

NXP Semiconductors

PCF2127A

Integrated RTC, TCXO and quartz crystal

8.11 Timer functions

The PCF2127A has two different timer functions, a watchdog timer and a countdown

timer. The timers can be selected by using the control bits WD_CD[1:0] in the register

Watchdg_tim_ctl.

• The watchdog timer has four selectable source clocks. It can, for example, be used to

detect a microprocessor with interrupt and reset capability which is out of control (see

Section 8.11.3)

• The countdown timer has four selectable source clocks allowing for countdown

periods from less than 1 ms to more than 4 hours (see Section 8.11.4)

To control the timer functions and timer output, the registers Control_2, Watchdg_tim_ctl,

and Watchdg_tim_val are used.

8.11.1 Register Watchdg_tim_ctl

[1]

Default value.

Table 34.

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

Bit

Symbol

Value

Description

7 to 6 WD_CD[1:0]

00[1]

watchdog timer disabled;

countdown timer disabled

watchdog timer disabled;

countdown timer enabled

if CDTIE is set logic 1, the interrupt pin INT is

activated when the countdown timed out

watchdog timer enabled;

the interrupt pin INT is activated when timed out;

countdown timer not available

watchdog timer enabled;

the reset pin RST is activated when timed out;

countdown timer not available

5TI_TP

0[1]

the interrupt pin INT is configured to generate a

permanent active signal when MSF and/or CDTF is set

the interrupt pin INT is configured to generate a pulsed

signal when MSF flag and/or CDTF flag is set (see

Figure 25)

4to2 -

unused

1 to 0 TF[1:0]

timer source clock for watchdog and countdown timer

4.096 kHz

64 Hz

1 Hz

11[1]

⁄

60 Hz

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