Control Logix Indirect Address'

[hipoint2 0]

Does anybody know if you can use an expression for a indirect address'. For example ADD(Test[whocares-1],1,test2);

[TimWilborne 108]

Yes except the whocares-1. The "-" is an invalid charactor Misunderstood the question. No I'm pretty sure you can't

[TConnolly 13]

As long as Test is an array and Whocares is a DINT tag, you can do that. I first assumed that was Whocares minus 1, which is a valid expression, but not embedded in a ladder ADD instruction. You can embed that in a CPT instruction however or in ST. CPT Test2 "Test[Whocares - 1] + 1" Edited 1 Aug 2006 by Alaric

[TimWilborne 108]

Actually Alaric it looks like it is a valid expression. I just tried it and it worked. Only one catch. If whocares is 0 then it points to -1 and faults the processor.

[hipoint2 0]

That would explain why I couldn't find the darn thing in the tag database. The new things that you learn about these Logix controllers. Thanks again.

[TConnolly 13]

Well I'll be dipped. I learned something too. I would have thought it was valid only in a CPT instruction. I'll have to give this a try myself. I've got a CompactLogix at my desk I can try it on.

[TimWilborne 108]

Ok I've played with it and can't find any snags in it besides watching not to point outside the data boundary. Hipoint, I wold still use caution in using this method It does not work with the Micrologix 1100 so I'm guessing that it doesn't work with any RsLogix 500 products