Living with A-B ControlLogix v20.19

A third-party has upgraded one of the PLCs to A-B ControlLogix v20.19, and as noted in several other posts, this is a worst-case scenario for the Ignition OPC-UA driver. Direct memory access is disabled, so the legacy ControlLogix driver doesn’t work, and it does not use the v21+ protocol, so while the new Logix Driver technically works, performance is severely degraded.

I’m currently trying to determine if we can get a copy of v20.18 or earlier to downgrade to, or if their software will support upgrading to v21 or higher. Should neither of those be possible, does anyone have advice on how to configure the driver do get better performance out of it? Or if there are changes we can make to our scan classes and transaction groups?

I’ll see if we can do some testing this week to confirm and update the descriptions you asked about in the other thread.

I think the line where they turned off direct memory access is at maybe firmware 20.15? I know 20.11 does work with the legacy driver. Not sure beyond that.

Mmm, we might not be able to do this testing after all. Seems Rockwell isn’t allowing downloads of “retired” firmware versions any more…

That’s what our vendor said when I asked him about the possibility of downgrading. He suggested that we might be able to open a special request from Allen-Bradley, but didn’t sound hopeful. If he can’t upgrade to v21 or higher for some reason, we’ll have no choice but to make this work somehow.

Consider using FactoryTalk OPC server instead of our driver for these worst-case firmware versions. They use some proprietary and undocumented tag access services that perform better.

You might also consider moving critical data traffic to a class 1 connection… (shameless self-promotion):

It is possible to move a substantial amount of tag data at blistering-fast rates (compared to a polling connection) no matter what firmware is involved. Some code required on the PLC side, though.

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So we did manage to get ahold of “retired” firmware versions and so far we have confirmed that v20.18 (and .13 and .14) does work with the legacy driver but v20.19 does not.

Additionally, we confirmed that despite v20.19 removing the direct memory access it did not also add instance-based access that lets the newer driver access tags more efficiently, so you are indeed stuck with using the newer driver in its fallback symbolic access mode.


Fortunately we determined that there was no reason from any technical standpoint not to upgrade it to v21. That just required some downtime to modify the PLC, and a little configuration tweaking to get the OPC Item Paths right for the new driver.