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Adding a useless instruction changes the program? WHILE loop

Created by: Jeremy Mahieu at: 12/19/2013 2:06 PM (2 Replies)

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12/19/2013 2:06 PM	Rate (0)
Jeremy Mahieu Posts: 101 Rating: (6)	Please take a look at the screenshot attached. It shows the online monitoring of a program in a simulation plc. TIA Portal V12SP1, S7-300 PLC, SCL Language The program was not behaving as I would have expected it so I tried to monitor. But the monitoring gives me only questionmarkts. First question: Why is it not monitoring properly? Then I add this meaningless instruction to be able to monitor A:=A. I can now monitor but this has changed the workings of the program, it now works properly. WHY?!! (=second question). (I can repeatably test this. If I do not add the dummy commands the loop will not execute.) (P.S.: When will they allow .png in here? The same in image is 5 times bigger in jpg and of terrible quality.) Attachment SiemensAwesomeness.jpg (154 Downloads)
Jeremy Mahieu Posts: 101 Rating: (6)	Last edited by: Jeremy Mahieu at: 12/19/2013 2:31 PM Last edited by: Jeremy Mahieu at: 12/19/2013 2:15 PM
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12/19/2013 3:01 PM	Rate (0)
0_Einstein Diamond Expert Joined: 7/7/2010 Last visit: 12/9/2023 Posts: 13994 Rating: (2283)	Jeremy Mahieu Please take a look at the screenshot attached. It shows the online monitoring of a program in a simulation plc. TIA Portal V12SP1, S7-300 PLC, SCL Language The program was not behaving as I would have expected it so I tried to monitor. But the monitoring gives me only questionmarkts. First question: Why is it not monitoring properly? Then I add this meaningless instruction to be able to monitor A:=A. I can now monitor but this has changed the workings of the program, it now works properly. WHY?!! (=second question). (I can repeatably test this. If I do not add the dummy commands the loop will not execute.) (P.S.: When will they allow .png in here? The same in image is 5 times bigger in jpg and of terrible quality.) Sounds like a simulator bug to me. Submit to Support Requestis my suggestion.
	science guy
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12/19/2013 3:46 PM	Rate (0)
Jeremy Mahieu Posts: 101 Rating: (6)	Ok reported. I wish I could try this on a real PLC. I doubt they will bugfix their simulator (if that really is the problem) since the new version is in use already (for S7-1500).
Jeremy Mahieu Posts: 101 Rating: (6)
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