SLC500 Long Scan Times

[mjp123gp]

I have a 1747-L552 that has been getting occasional scan times over 1 second. The normal average on this processor is around 20ms but about once a week I can check the status page and see the high scan time. It's been running about a week now since I reset the max and it hasn't done it yet.Any ideas what would cause this? Could I add logic to each routine to find out if the hold up is in the same routine every time?

Thanks

 

[Maxkling]

Are there any label and jumps that might be looping?

Any serial communication going on?

 

[mjp123gp]

I can't find any jumps in the routines. We are using serial for ASCII writes to a message display.

 

[James Mcquade]

I had the same issue several years ago and the only thing we could attribute the scan time issue to was on line edits. as we proved the machine, we found issues and did online edits to fix the issues. the plc scan time kept getting slower. we saved the program to the pc, made a change and undid the change off line, recompiled the program and then downloaded it back to the plc. Sounds crazy, but it fixed the scan issue.

regards,
james