Datasheet

PCF2127AT All information provided in this document is subject to legal disclaimers. © NXP B.V. 2013. All rights reserved.
Product data sheet Rev. 6 — 11 July 2013 37 of 86
NXP Semiconductors
PCF2127AT
Integrated RTC, TCXO and quartz crystal
8.11 Timer functions
The PCF2127AT 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 microcontroller 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 35. 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
01 watchdog timer disabled;
countdown timer enabled
if CDTIE is set logic 1, the interrupt pin INT
is
activated when the countdown timed out
10 watchdog timer enabled;
the interrupt pin INT
is activated when timed out;
countdown timer not available
11 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
1 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
00 4.096 kHz
01 64 Hz
10 1 Hz
11
[1] 1
⁄
60
Hz