Am I correct in thinking that Ignition reads directly from a PLC memory area, regardless of where the PLC is in a scan?
i.e. If I were to turn a bit on at the top of a PLC program, then it turns off down the bottom, the tag could be read by Ignition at any point in time, including during the scan. Thus, it could be read as on, despite the fact it turns off during the program scan.
That is an implementation detail that is likely unique to every PLC brand and model. I’m not sure I could answer that with confidence even if you did specify one.
It is definitely true for all ControlLogix and CompactLogix processors. It is even true for those processors physical inputs and outputs.
I already planned to structure the PLC program accordingly.
It will likely affect some Customers who have program structures in place as a standard, but I can at least explain why there may have to be accommodations for altering these.
Did you mean to post that in the thread about AOIs?
No, I did mean this thread, but I guess it applies to both.
Once you know both of these things it helps in planning tag and program structure.
People here are always quick to respond with relevant and helpful guidance.
It makes the transition to using Ignition so much easier.