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Simatic CPU 315-2DP (STOP caused by diagnostic interrupt (OB not loaded or not possible, or no FRB)

Created by: jp0223 at: 9/29/2021 7:15 PM (6 Replies)

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9/29/2021 7:15 PM	Rate (0)
jp0223 Posts: 6 Rating: (0)	Dear Expert I have Siemens S7 314C-2DP CPUlast week we were running on live production when suddenly got a fault on the PLC it automatically go to stop and give SF error on cpu. I hooked up on the PLC and opened the diagnostic buffer I attached the diagnostic buffer errors, thanks and a lot and hope you guys can help me to resolve this issue Attachment Diagnose.txt (740 Downloads)
jp0223 Posts: 6 Rating: (0)
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9/29/2021 8:31 PM	Rate (1)
Havillant Comet Silver Member Joined: 8/6/2018 Last visit: 1/15/2026 Posts: 366 Rating: (46)	Hello, CPU goes into Stop because there is no OB121 loaded.This OB is called when the CPU detected a programming error.load the OB121 and the CPU will not go into Stop.

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9/29/2021 9:53 PM	Rate (1)
dchartier Grandmaster-Expert Joined: 9/27/2006 Last visit: 1/16/2026 Posts: 12481 Rating: (2722)	Hello jp0223; Your diagnostic buffer shows the 2 error messages in the screenshot blow repeatedly, and they seem to be linked. OB 121 is a diagnostic OB called by the CPU's operating system when a programming fault is detected.somehere in your blocks. As Havillant Comet already suggested, if OB 121 is created and present in CPU mempry when it is called, then the CPU will stay in Run (if at all possible) even when the fault is present; the SF LED will remain active to tell you to correct the error.. Since you do not have an OB 121 in your program, the CPU goes to Stop when a programming issue is reached. So start by opening the Blocks foder, create a New block, call it 121, save, compile and download it (as is, no programming necessary for the moment) to the CPU. Not only should the CPU remain in Run, but next time the diagnostic buffer is opened, it should contain more information on the source of the fault, since diagnostic OB interface provide a "handle" for the OS to interrogate the system faults. The diagnostic buffer also tells you that the fault has occurred in FC 22. Do you have a block called OB 22? Open it, examine it and see if something looks strange inside your code. If you have trouble understanding it, please copy it and share it with us here. Hope this helps, Daniel chartier Attachment jp0223 recurrent errors diagnostic buffer.jpg (709 Downloads)

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9/30/2021 3:54 AM	Rate (0)
jp0223 Posts: 6 Rating: (0)	Thanks for the advice guys, to be honest I'm just learning and do have any proper training on the PLC programming and just learn as it goes by and watching some tutorial videos, apparently I just only have a trial version of the Step 7 and ima get the activation keys in 2 days. and I know its too much but can you guys guide me and help me step by step to resolve this issue. I attached the blocks that's in our program. Appreciate you guys help too much. Attachment PROGRAM BLOCK.png (722 Downloads)
jp0223 Posts: 6 Rating: (0)
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9/30/2021 4:18 AM
Nellerbe Posts: 4 Rating: (0)	Hey JP
Nellerbe Posts: 4 Rating: (0)
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10/2/2021 12:14 PM	Rate (1)
Duris_I Diamond Member Joined: 4/28/2015 Last visit: 11/27/2025 Posts: 10970 Rating: (844)	Hello, jp0223 Thanks for the advice guys, to be honest I'm just learning and do have any proper training on the PLC programming and just learn as it goes by and watching some tutorial videos, apparently I just only have a trial version of the Step 7 and ima get the activation keys in 2 days. and I know its too much but can you guys guide me and help me step by step to resolve this issue. I attached the blocks that's in our program. Appreciate you guys help too much. your screenshot looks to me like in Online mode, no expected. Look in Offline in your prj so I expect you don't have there OB121. As Daniel already sugested to you, create block and download it to CPU. If you'll do correctly OB121 you can then see it as other OB121 with your existing blocks. Then click on it with right mouse button and download it to CPU. This can be correct way.
	With best regards... Ivan Duris Flight: OMICO
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10/4/2021 5:39 AM	Rate (0)
jp0223 Posts: 6 Rating: (0)	thank you guys for all your help and advice, our system are up and running, I just load the OB121 offline and download it, greatly appreciate all the help.
jp0223 Posts: 6 Rating: (0)
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This contribution was helpful to 1 thankful Users Duris_I

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