G_DeMark

Major Fault

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I have a compact logix with a major fault.

Please see my attached file for the complete fault message. 

Code 20 array subscript too large. or control data type to large or invalid.

Has anyone observed this issue before.  The PLC is a compact logix model.  Every time, the controller is switched from program to run the major fault occurs within 5 seconds.  The fault can be cleared but then it comes back in a few seconds.  I have been told by my tech that no program changes have been made.  Could there be a hardware/wiring issue?

Thanks much

Document_1234.pdf

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What is the size of the arrays used in your message instruction?

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Hi,

Please check that your "MESSAGE_WORD_RESULTS" array is at least 32 elements. This array will hold the bit numbers that are different. If you have, for example, a result array length of 5, but there are 6 or more bits that differ (between the Source and Reference words), the Major fault code you described will be raised.

see page 626 onwards: http://literature.rockwellautomation.com/idc/groups/literature/documents/rm/1756-rm003_-en-p.pdf

good luck,

vds

Edited by vds
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Yes, you gentlemen were correct.  I increased the "MESSAGE_WORD_RESULTS" array to 32 elements and all is good.  Thanks very much for your help.  I would have had no idea without your help.

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Thanks for letting us know what you found. I would recommend adding a ring of code so that that array index ends up being greater than the array size, it moves the safest possible value back into it and sets some alarm.

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