Reading several tags as one telegram

Ignition
1

I am new to Ignition (but have been through all the online training material), have worked with e.g. Aveva Wonderware for several years.

We have a usecase, where I have to read e.g. 25 tags in one block, they consists of one telegram, that I need to interpret in a certain way and move the data to the appropriate location in my Ignition UNS. E.g. when a trigger is raised, I need to read my telegram, because I then know that is has been updated appropriate from my PLC code.

Can I do something similar in Ignition ? Mostly with Siemens PLCs but also AB

2

If you mean this needs to be a single message between Ignition and the PLC, then yes, you can do this with system.opc.readValues(), which bypasses the Ignition tag system.

For it to truly be a single request, you typically must place all of the values in a single structured tag (Logix) or single data block (Siemens). This is what permits all of the PLC items to be optimized by the driver into a single operation.

3

Hi.

And thanks.

I did see the function system.opc.readValues() as you mention but was unsure if it actually reads through to the PLC.

Would you then use the PLC tag directly in the read or the Ignition tag bound to the PLC tag?

4

It reads directly from the OPC Server, which in turn means a read directly from the PLC.

The system.opc.readValues function expects OPC Item Paths (NodeIds), not Ignition Tag Paths.

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