Writing Arrays Using OPC/RSLinx


Thread Starter

C. Tovey

I'm relatively new to OPC so excuse me if this is a stupid question.

I have many tags in a ControlLogix PLC, all of which are real. I have software using OPC to read and write them all no problem.

In order to speed up data transfer, I attempted the following approach: Declare an array in the PLC (say X = REAL[10]) and alias the old tags to this array. My code to write tags indivually still works.

I can read the array using OPCItem.Read with e.g "X[0],L10,C1". It returns a variant/single(0,9) containing the data.
On the very next line of VB Code, I call OPCItem.Write with the variant returned by Read, and it all the array to 0.0. I tried using SynchWrite at OPCGroup level, and got the same result.

I have RSLinx 2.30.01 Build 48.

Any one have any clues ?