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slcman

instruction search

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I suppose a hudge program in a S7-300 use stop command. How I can search a instruction in ladder with step 7? I would like to check the condition for stop the program. Thanks

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To stop a Siemens, you would call SFB20 - STOP. Thois is usually in one of the diagnostic OB's. If a fault occurs and the relevant OB has not been programmed then the PLC will stop. If the OB has been programmed, then the PLC will not stop unless the block SFB20 is included.

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I never talk about fault. S7-200 have a STOP instruction, I think S7-300 have too! How I can search a instruction.

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S5 also had a STOP instruction, S7-300's and 400's do not. SFB20 is the only way to program a STOP in these PLC's. I don't believe there is a method to search instructions in Step 7 either, short of converting to a text file and doing a word search. You never talked about fault, I did! Because in 300's and 400's the fault OB's are where you would in normal circumstances find SFB20. There is of course nothing stopping anyone program SFB20 in normal code, it just isn't normally done.

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I am not 100% sure about this, but I believe that the cause of the CPU going into stop will appear in the diagnostics buffer of the CPU. I know it is so if the cause is a fault or the user stopping it via STEP7. So I guess it will be the same if the program is stopped with SFB20. At least that will tell you if you have to look for SFB20.

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I'll check for SFB20, but something is strange; fault light is OFF! It's the reason why I didn't check for a fault and start to look for STOP instruction. thanks I'll check and leave the result

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The cause of the CPU stopping shall always be observable in the Diagnostics Buffer. A stop by STEP7 will be called "stop request by user" or something like that. Such a stop type will not cause the FLT light to go on. I just read up on SFB20, and now I am not so sure that it can be used to stop a CPU. It says in the help text that it is for "remote devices", and I think that it is only relevant with communication processors.

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Your correct I'm wrong, I did not have access to my Siemens manuals and searched another forum for stop block. The STOP block to stop the CPU is SFC46, not SFB20. Sorry, my mistake.

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