Step 7 OB request error

Hello all.

A rather unique problem has showed it self to me. I have 2 identical machines that run Siemens S7-300 PLC's. One machine works fine but the other stops mid cycle and I could find out why until I looked at the diagnostic buffer of the PLC. This is the error that is output when the machine stops.
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OB request error
No relevance for user (Z1): 0000
Cause Cyclic interrupt clock pulse generator 6
Causing OB: Cyclic interrupt OB (OB35)
Causing priority class 12
Requested OB: Timing Error OB (OB80)
Internal error, Incoming event
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The code has not been changed at all on the PLC's. And I don't even use the cyclic interupt for any function. So I can't understand why this is happening just on ONE machine? Could it be a defective CPU? What can I do to resolve this problem? Any input would be great...
Thanks in advance.
Regards
Ales

Hi Ales

Is the faulty PLC using the built in clock?

Go to Hardware config and 'object properties' of the PLC and see if the Cycle/Clock Memory tab has something in the Clock Memory (normally a marker word).

It looks like this could be something to do with the fault reading between the lines of your diagnostic buffer.

Cheers

;-)

Is OB35 present in the online and/or offline projects ?
If so, and since you dont use OB35, delete OB35 from both online and offline.

edit: Something like this can happen if you reuse an MMC card and dont completely delete it before starting using it in a new CPU.

Thanks for the input.
I will try what you proposed to me next week, when I am on site and report back. Hope it works... I also checked, the execution time is set to 5ms. Should I try to enter a bigger value if the previous (deleteing OB35 from online and ofline) doesn't work?

Thanks.
Best regards
A

5 ms is relatively low.
If there is dormant code in OB35, maybe completely bogus code because it origins from another program, then the code may take longer than 5 ms to execute, and you will get an error - could be the OB80.
Deleting OB35 should do the trick if this is the reason.

Guys, I was reading the feedback to this case but I have one point that needs your expertise.
If the computer runs a virtual PLC, and for long time no problem occur, then it start to have this problem reported. (nothing was change in the software). Can be a hardware problem (like, memory, HD, raid card. etc..) that is causing this? If yes, what is the most probably one that could be causing this?

Thanks!

Hello Flavio,


Welcome to the forum. I would recommend you start a new topic.