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Strange Jump Behaviur

Created by: Mohammad Razmjoo at: 2/13/2022 7:17 AM (7 Replies)

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2/13/2022 7:17 AM	Rate (0)
Mohammad Razmjoo Posts: 99 Rating: (0)	According to my text book exercise these program (attached by picture) must act like this: These codes are written in OB1. Why after download these program is no problem for a while but after that, CPU go to STOP mode? I test these program by PLCSIM. But it is functioning very strange. RLO is not function normal in that comparator. And CPU never go to STOP !! And after the first time RUN if I do STOP_RUN again or do COLD RESTART, the value of the MW0 is set to 1000 instead of zero (0) . Why???!!! Even after MRES , the MW0 value is not ZERO (0)?!! What the hell ?! Hasan Sabbah Attachment JUMP Bug topic.JPG (432 Downloads)
Mohammad Razmjoo Posts: 99 Rating: (0)
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2/14/2022 7:59 AM	Rate (0)
bit7 Bronze Member Joined: 7/26/2008 Last visit: 1/16/2026 Posts: 110 Rating: (20)	Hi Hasan, perhaps you can explain what it is that you are trying to achieve. Looking at the code, what I see is that you have created a loop that will count to 1 000 and then exit, but all in one scan. Online display might have difficulty in showing what is happening.

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2/14/2022 2:35 PM	Rate (0)
Mohammad Razmjoo Posts: 99 Rating: (0)	According to the book, it must lead CPU to STOP mode. but It does not. max scan cycle time is 150ms and counting until 1000 take time more than 150ms. isn't it??
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2/14/2022 2:41 PM	Rate (0)
Mohammad Razmjoo Posts: 99 Rating: (0)	If you try this with PLCSIM you will see that the logic does not work like you said. it count until 32767 and the go negative.
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2/15/2022 2:56 AM	Rate (1)
fritz Diamond Expert Joined: 10/7/2005 Last visit: 1/16/2026 Posts: 3054 Rating: (1062)	Hasan Sabbah According to the book, it must lead CPU to STOP mode. but It does not. max scan cycle time is 150ms and counting until 1000 take time more than 150ms. isn't it?? According to which book? Suggest you grab yourself the Instruction manual for your chosen CPU and check out execution times for each Instruction you have in your loop. You'll probably find that the CPU will crunch through the 1000 loops you do per OB1 scan in anywhere from 100 microseconds to max 2 ms or thereabouts (but - as said - it depends on the chosen CPU). It is either way a far cry from the 150ms scan time monitoring. Hasan Sabbah If you try this with PLCSIM you will see that the logic does not work like you said. it count until 32767 and the go negative. But of course it will as that is what you programmed it to do (i.e. count to 1000 in MW0 in the first OB1 scan, then to 2000 in the second OB1 scan and so forth)
	Cheers fritz The advice and opinion given in this thread is that of the author and does not necessarily reflect the views of I S Systems Pty Limited. To find out how I S Systems can help you with your automation needs please visit www.issystems.com.au.
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2/15/2022 3:54 AM	Rate (1)
Med_selmi Silver Member Joined: 4/17/2018 Last visit: 6/23/2025 Posts: 262 Rating: (61)	fritz Hasan Sabbah If you try this with PLCSIM you will see that the logic does not work like you said. it count until 32767 and the go negative. But of course it will as that is what you programmed it to do (i.e. count to 1000 in MW0 in the first OB1 scan, then to 2000 in the second OB1 scan and so forth) Not exactly every scan it will count 1000. Because in this program it will increment mw0 until 1000 only first scan then every scan mw0 will be incremented by 1 until 32767. And that's why Hasan said when restart PLC, MW0 start at 1000. But in reality mw0 start at 0 and after first scan it reaches 1000

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This contribution was helpful to 1 thankful Users fritz

4/8/2022 9:33 AM	Rate (0)
Mohammad Razmjoo Posts: 99 Rating: (0)	OK!! It does not stop and I think book has mistake. But Why does it count strangely. You are wrong, it does not count like this you said. first cycle count to 1000 and after that in every cycle only +1 to mw0... .Every time I Startup again it begin from 1000!!
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4/8/2022 9:34 AM	Rate (0)
Mohammad Razmjoo Posts: 99 Rating: (0)	Yea. that's true.
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