Siemens SIMATIC S7 - Page 355

Program instructions
7.13 Program control
S7-200 SMART
System Manual, V2.3, 07/2017, A5E03822230-AF
355
Example: STOP, END, and WDR (Watchdog reset) instructions
LAD
STL
When an I/O error is detected,
force the transition to STOP
mode.
Network 1
LD SM5.0
STOP
When M5.6 is ON, execute the
watchdog reset instruction to
extend the allowed scan time by
500 milliseconds.
Network 1
LD SM5.6
WDR
When I0.0 is ON, terminate the
current scan.
Network 1
LD I.0
END
Note
If you expect your scan time to exceed 500
ms, or if you expect a burst of interrupt activity
that prevents returning to the main scan for more than 500
ms, you should use the watchdog
reset instruction to retrigger the
watchdog timer.
Use the watchdog reset instruction carefully. If program execution loops prevent scan
completion or excessively delay the completion of the scan, then the following processes are
inhibited until the scan cycle is completed.
•
Communications (except Freeport mode)
•
I/O updating (except Immediate I/O)
•
Forced values updating
•
SM bit updating (SM0, SM5 to SM29 are not updated)
•
RUN-time diagnostics
•
STOP instruction, when used in an interrupt routine