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Displaying SLC Errors
Displaying SLC Processor Errors
By Ben Brechtel on 12 December, 2002 - 2:53 pm

Does anyone know if it is possible to display the error and error description from the SLC processor to a external serial device such as a LCD? Can this info be sent out even if the SLC faults?

Any input is greatly appreciated!

You can read the addresses as the SLC processor sets bits for each error. If you are using something like a PanelView or other device, you can read these bits and associate text with them in your OIT. That is one way.

By T. Connolly on 13 December, 2002 - 4:18 pm

You cannot send the error code out if the PLC program is not operating, ie, faulted. However error codes and bits can be read by any device able to communicate with the PLC via DF1. I strongly suggest you write an error handler and recovery routine as part of your program to trap and correct minor errors before the scan ends and they cause a fault. This routine can also generate alarms as needed. You put the fault routing number in register S:29. Your major fault code is found in register S:6. Major error halt bit is S:1/13. Minor error bits are in S:5. You can check and clear minor error bits in the course of your program and I highly recommend it if you are doing any significant math, especially the overflow bit, S:5/0, as it will cause a fault if it is not cleared before the scan ends. The S:1/13 bit is useless as an input instruction in your ladder logic because if it is set your ladder stops executing, but I have seem programs where it is still in the code. I think the programmer was missing some fundamental understanding there. S:1/13 can also be read by any DF1 comm device however. You can also have your program set user defined faults and error codes if you wish.

Refer to your documentation or download the SLC500 instruction set reference from manuals on line at http://www.ab.com.

By Bob Peterson on 13 December, 2002 - 4:18 pm

The errors are encoded within the processor status ("S") file. There is no reason you cannot display these on an external serial device such as a Panelview. The status table is available even if the CPU has faulted, as long as it is not scrambled.

The external device would need to read the status info and display it. The serial port would not be under PLc control if it left run mode due to a
fault.

Bob Peterson

By Jeremy Pollard on 14 December, 2002 - 3:14 pm

Available in the status file - a read function is required since the scan is stopped. Some SLC's have a fault routine that is run on an error (I think) like the PLC5's. the data could be sent out in this routine

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