Hardware Manual PCD1.M2110R1 │ Document 27-619 │ Version ENG 04 │ 2018-08-20
Saia-Burgess Controls AG
Watchdog (Software)
CPU / Control Process Unit
3-15
3
3.10
Watchdog (Software)
The hardware watchdog offers maximum security. A software watchdog can
be sufficient for non-critical applications, whereby the processor monitors itself
and the CPU is restarted in the event of a malfunction or a loop. The core of the
watchdog software is the instruction SYSWR K 1000. The watchdog function is
activated when this instruction is output for the first time. It must then be output
at least every 200 ms, otherwise the watchdog will be triggered and the PCD
restarted
Instruction in AWL code:
Label
Com
-
mand
Operand Comment
SYSWR
K 1000
; Software watchdog instruction
R/K x
; Parameter according to the following
; table
; K = Constants or
; R = Register
; Blank space
; x = 0 The software watchdog is deacti-
;
vated.
; x = 1 The Software Watchdog is activat-
;
ed if the instruction is not
;
repeated within 200 ms, a cold
;
start is performed.
; x = 2 The Software Watchdog is activat
;
ed if the instruction is not
;
repeated within 200 ms, XOB 0 is
;
called, then a cold start is
;
performed.
“XOB 0” calls are entered in the PCD History as follows:
«XOB 0 WDOG START» if XOB 0 was triggered by the watchdog software
«XOB 0 START EXEC»
if XOB 0 was triggered by a power supply error
