Saia-Burgess Controls AG
Hardware manual for PCD3 series │ Document 26-789 ENG19│ 2018-06-29
Software watchdog
PCD3.Mxxx0 Classic CPU and expansion enclosure
3-44
3
3.16 Software watchdog
The hardware watchdog provides a maximum of safety. For uncritical applications,
a software watchdog can be adequate, whereby the processor monitors itself and
the CPU is restarted in the case of a faulty function or a loop.
The core of the software watchdog is the SYSWR K 1000 command. The software
watchdogfunctionisactivatedwhenitisrstcalledup.Thereafter,thenamed
command must be called at least every 200 ms, otherwise the watchdog triggers
and restarts the control.
Command: SYSWR K 1000 ; Software watchdog command
R/K x ; Parameters according to the table below,
; K-Konstante oder Wert in Register
; x = 0 The software watchdog will be
deactivated
; x = 1 The software watchdog will be activated;
if the command is not repeated within
200ms, a cold start takes place
; x = 2 The software watchdog will be activated;
if the command is not repeated within
200ms,theXOB0willbecalleduprst,
followed by a cold start.
XOB 0 call-ups are entered in the Saia
PCD
®
history as follows:
“XOB 0 WDOG START” if XOB 0 was
called by
the software
watchdog
“XOB 0 START EXEC” if XOB 0 was
called because
of a supply
error
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