I am trying to see tags inside an AOI. I went back to basics and dragged and dropped the tags from the OPC browser into the Tags Folder, but the quality is bad and there is a red x next to them. What is more confusing is that some are working and some are not. I cannot see any similarities between…

[image] nminchin: SCADA can set the tag and then the PLC will reset it immediately without actioning anything Generally, you'd have the bit unlatch only after the desired action is performed. that way, if the cmd bit goes high during that rung's scan, it will persist until the next scan.

I always buffer my HMI commands at the beginning of my AOI (literally do a COP of my entire .Cmd tag to another identical tag, then only use that tag for logic and reset any bits processed as soon as they're processed (in both tags - buffered and unbufferred even though I really only need to do the …

There are two approaches I recommend: The simpler approach is to use short integers instead of booleans to fire events, like a reset pulse. Simply increment the tag, rolling over, and perhaps skipping zero. The PLC would notice the change and fire the boolean for you, for one scan (or whatever is…

First option sounds good! I'll look at using this from now on, thanks for the advice

Also, was I on the right track re the race condition if both scada and plc write to the same tag in a scada set plc reset setup?

That's one. The more common is a hiccup reading back while the PLC proceeds to set another signal, not realizing SCADA hasn't caught up.

Is this still in the same scada set / plc reset scenario, or would that be for other scenarios where the plc is writing other values, maybe set points

Here's an example, from PlantPax, that I use often. I will set OCmd_Start from the HMI and the PLC will immediately reset. Is it being suggested that the HMI could get stuck high? I ask because I have done this for a long time and have never seen it cause any issues. I have seen "stuck bits" using m…

Same here, I set the bit, the PLC resets it. Never had an issue with doing commands like this, and never had a bit get stuck.

It's not the PLC tag that gets stuck, it's the SCADA tag that gets stuck occasionally for me. I'd like to understand it more technically ( @pturmel @Kevin.Herron ?), but it seems like the subscription gets stuck. SCADA writes to the tag setting it True, the PLC immediately resets it to False, but SCAD…

Cannot read some tags inside Rockwell AOI

Ignition Early Access

Kevin.Herron February 18, 2025, 11:49pm 85

This is a race condition that can happen if you use the "Read After Write" option in tag groups with an OPC UA subscription. Not sure about other causes.

from Indirect Tag Delay - #9 by Kevin.Herron