AB driver question

I am getting this error on an AB driver.


I have 3 other connection exactly like this one and they do not have this error. what can I look into to resolve this error?

Usually that error code means either External Access is “None” in the PLC program for that tag or that it doesn’t exist all together.

Maybe this is a dumb question:

The AB driver, it auto browses and creates a tag list from that in the OPC quick client correct?

I am checking the permissions in the PLC.

Yes, you can see the tags it was able to browse in either the Quick Client or the OPC Browser in the Designer.

OK, so I checked the PLC and I dont have ant security restrictions on the PLC itself.
Here is the tag from the PLC:
image
And here it is being read from the OPC quick client:
image

So im kinda confused: is it reading, really? LOL

It did not read. In the PLC, go to the editing tab of the tag viewer instead of the monitoring tab, and scroll to the right until you see the external access column.

Oooo! You are using the Legacy ControlLogix driver. You should be using the modern Logix driver.

Maybe. Not if he’s on an older firmware version.

I’d expect an error in the gateway logs after you attempted that failed read.

True enough. But it browsed, and this is typical behavior for that case.

Right… maybe I was charitable to assume it was just this one tag he’s having an issue with and not all tags from that device.

If that’s the case then yes, one common reason for being able to browse but not read is that you hooked the legacy driver up to a v20.19/v21+ controller.

@mjohnson0238 can you clarify

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Yeah, its not reading any of the tags. On that PLC, the 3 other PLCs are reading and setup on same legacy module. My revision of the processors is v20.

Not enough detail, the full version matters.

Bingo. You need the newer Logix driver for this firmware version. It will perform much worse than your other legacy driver connections, so hopefully you don’t need too many tags.

Rockwell disabled the direct memory access mechanism used by the legacy driver mid-20.xx firmware series, but didn’t provide the replacement until v21+. The newer driver connected to an older firmware will read using symbolic access, which is quite a bit slower.

OK, thanks. I understand whats going on now.

That got it! thanks alot for the help fellas!

Watch out for slightly differing OPC Item Paths between the two drivers… it’s a gotcha if you’re trying to use a common UDT or something.

Good to know sir!