RSLogix5000 V20.01 NEQ not working as expected

Jeebs

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Join Date
Feb 2007
Location
Leuven
Posts
1,059
Hi,

So I have a piece of code that's identical on 2 machines. Both L62's running on RSLogix 5000 V20.01. Check var1 with var2, if NEQ then do logic and MOV var1 to var2. On one machine you do it once and the NEQ then skips the logic once the values are identical. On the other machine it does the logic regardless of whether the variables are identical or not. It does the logic each and every time. It writes var1 to var2 and next scan it thinks the values are different again.

What could cause this behavior and what can I do to fix it?
 
What kind of datatype are you using for var1 and var2? Be sure it's not Real.

I agree if one is REAL and the other is not. If both are REAL, then something else is going on. I would be looking for other destructive references to var2, or possibly external access.
 
Can you upload the code? I've never seen such an issue with the NEQ instruction. I'm wondering if you have an unusual rung structure and scantime which updates the values immediately after the comparison.
 

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