Hardware Manual PCD 1 / PCD 2 Series│Document 26 / 737│Edition EN 15│2008-07-22
Saia-Burgess Controls AG
Monitoring the CPU (watchdog)CPUs and expansion housings3
3.17.3 Software watchdog for PCD1 and PCD2
The hardware watchdog provides maximum security. However, for non-critical
applications, a software watchdog may be sufficient, whereby the processor monitors
itself and the CPU is restarted in the event of a malfunction or a loop.
The core of the software watchdog is the instruction SYSWR K 1000. When this is
first issued, the software watchdog function is activated. This instruction must then be
issued at least every 200 ms, or the watchdog will trigger and restart the controller.Instruction: SYSWR K 1000 ; Software watchdog instruction
R/K x ; Parameters as per table below
; K constant or value in
; register
x = 0 The software watchdog is deactivated
x = 1 The software watchdog is activated; if the instruction is not
repeated within 200 ms, there is a cold start
x = 2 The software watchdog is activated; if the command is not
repeated within 200 ms, XOB 0 will be called, followed by a
cold start.
XOB 0 calls are entered in the PCD history as follows:
“XOB 0 WDOG START” where XOB 0 has been invoked
by the software watchdog
“XOB 0 START EXEC” where XOB 0 has been invoked
because of a supply fault
In order to use the software watchdog, the following minimum firmware versions are
required:CPU type Minimum firmware
version
PCD1.M1x0 001
PCD1.M1x5 001
PCD2.M110/120 080
PCD2.M150 0B0
PCD2.M170 010
PCD2.M480 010PCD2.M480: The status of the watchdog relay can be read via I 8107
"1" = watchdog relay on