Hardware Manual for the PCD2.M5 Series│Document 26/856; Version EN 12│2014-07-24
Saia-Burgess Controls AG
Software watchdog
PCD2.M5_ Classic CPUs and expansion housings
3-52
3
3.16
Software watchdog
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 will be a cold start
x = 2
The software watchdog is activated; if the instruction is not
repeated within 200 ms, XOB 0 will be called and then there
will be 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
