RSLogix5000 What's wrong with this CMP statement?

evanmars · Oct 22, 2021

RSLogix 5000

I am getting a 'CMP, Operand 0: Invalid expression.' for this. It's been a long week, I can't see the problem.

(a = (b + 1)) OR (a = 1)

RockyLeafs · Oct 22, 2021

Dont believe you can have nested brackets....

Operaghost · Oct 22, 2021

evanmars said:
RSLogix 5000

I am getting a 'CMP, Operand 0: Invalid expression.' for this. It's been a long week, I can't see the problem.

(a = (b + 1)) OR (a = 1)

That is your problem. That is a True/False. You are essentialy checking if A = True or False. Let's Assume A = 5 and B = 10 and break that down.

TagA = TagB +1
This resolves to if 5 = 11 which is a valid statement but would be false with the current values.

OR

if TagA = TagA = 1 (5 = 5 = 1)
This of course does not make logical sense. For example, change that to A + 1 and you have a valid statement that the editor will accept.

OG

plvlce · Oct 22, 2021

You are using OR as your final comparison, but OR is a bitwise or, not a comparison.

L33er · Oct 22, 2021

drbitboy · Oct 22, 2021

(a MOD b) = 1

?

Although that would also return true for a := N*b + 1, when N is an integer.

Mispeld · Oct 22, 2021

Someone recently claimed a logical-OR was added to the Logix 5000 comparison expression operators, but as far as anyone replied it was not in version 30 or less if I remember correctly. Not sure if anyone checked the newer versions.

L33er · Oct 23, 2021

His OR logic did not make any sense to me, but the rung in the picture shown there were no error.

RSLogix5000 What's wrong with this CMP statement?

evanmars

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