SLC 500 - S:5/0 Math Overflow Trap

[Rob S.]

We are getting a fault......

Math Overflow Trap S:5/0 = 1

Apparently we are getting a value greater than 32767 or less than -32766. If I put a OTU S::5/0 at the end of the main routine. Will that prevent us from getting this "Math Overflow Trap" ?

Thanks in advance.

 

[kamenges]

Yes...for the most part. If you have an STI file designated you should put an OTU at the end of that also. The chances of an STI triggering AFTER an OTU at the end of LAD 2 but BEFORE housekeeping is pretty remote. But believe it or not I've had it happen.

Keith

 

[Rob S.]

Could you describe what you mean by "STI"

Thanks

 

[Mickey]

You will still get the overflow but it will not fault the processor.

See links for more on the subject.

http://www.plctalk.net/qanda/showthread.php?p=14307&postcount=4

http://www.plctalk.net/qanda/showthread.php?t=27164&highlight=Math+Overflow+Trap+S:5/0

http://www.plctalk.net/qanda/search.php?searchid=3538632

 

[Rob S.]

Just simply this , correct ?
S:5/0
------------------------------------- ( OTU )

 

[Mickey]

Just simply this , correct ?
S:5/0
------------------------------------- ( OTU )

Yup, at the end of ladder 2

 

[kamenges]

Originally posted by Rob S.:

Could you describe what you mean by "STI"

STI stands for Selectable Timed Interrupt. If you open your processor configuration file you will see a tab labelled "STI". This is where you configure your selectable timed interrupt. The STI, when used, is a program file that is called by the processor firmware at a rate specified by the user. This file is NOT called from the main ladder program. It is intended for logic that must operate at a more defined rate than the free-running, indeterminate rate it would execute if called from LAD 2. If you have been exposed to Logix5000 this would be the same idea as using a periodic task.

Keith