Is it possible to use system.tag.writeBlocking on a OPC tag?

Ignition
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Is it possible to use system.tag.writeBlocking on an OPC tag? I understand the tag could be written over, but if it is a leased tag that isn’t active and I want to get the value I can use system.opc.readValue to get it. Once I have the value it could be handy to update the OPC tag since it may not update anytime soon depending on the tag group settings. Maybe this isn’t considered a best practice and therefore isn’t allowed. It didn’t seem to work for me. I am using 8.0.14 of Perspective, but I assume this applies across all of Ignition.

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Why not? What happened? Was there an error message?

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I get [Good] back in the script console, but the value property does not update. The timestamp doesn’t either. Furthermore, if the tag is ‘Uncertain_InitValue’ it remains as such. As a test I took the tag off of leased and just on a slower direct tag and it still only updates on the tag group time. writeBlocking does not update it.

If I do the same thing to a memory tag both update right away.

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Maybe the underlying value in the device is being overwritten then?

Can you do a write to this tag from the quick client or tag browser?

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Well my original intent was to read the actual value using system.opc.readValue to avoid waiting for the tag group to update so then I would actually be writing to the tag with the value that is currently in the PLC. When the tag group updates next nothing would change. I was curious though if my test was being overwritten in the PLC, but the tag group setting has Read After Write off and to do another test I removed any rungs of logic in the PLC that would write to the tag. I then was able to toggle the value and also use writeBlocking BUT the changes wouldn’t take effect until the tag group time occurred again. So I could use writeBlocking but if the tag group updates ever 30000 ms I could wait 30 seconds to actually see it change in the tag browser. I just ran another test and it appears writeBlocking is changing the PLC value right away, but the Tag Browser does not update.

OK - after I realized that I turned on Read After Write and it does update the Tag Browser with the value. Problem solved. Thanks.

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