Bad Tag Values following PLC Reload (Allen Bradley)

Ignition 7.6.6
AB ControlLogix V20

Today we’ve had some issues following the PLC program being reloaded while Ignition was running. The first thing I noticed was that it still said “Connecting…Program Mode” even once the PLC was back in Run Mode.

I disabled the Device and then immediately re-enabled it. The status then went to “Connected…Run Mode” however I noticed that numerous tag values seemed to be “stuck” and didn’t mirror what was in the PLC. I did a “Refresh Browse” which seemed to kick a lot of them into life but there is still the odd one that was wrong, e.g. a Boolean that was ON in Ignition but OFF in the PLC.

Using OPC Quick Client showed it was ON (incorrectly) and quality GOOD.

I tried changing the OPC Path temporarily to (try to) release the OPC Subscription on the tag but as soon as I changed it back again I saw the incorrect value again.

Obviously Ignition is caching some information - e.g. when an online edit is done in the PLC it logs a message about “Processor Edit Number” changing. Is there a way I can force it to forget everything about a PLC (i.e. clear a cache) and then refresh it from the device, so hopefully it’s all up to date?

I’d hoped disabling and re-enabling the device would have done something like that but it doesn’t appear to.

I can’t really (or don’t want to) restart Ignition as there are other PLCs it’s currently connected to and logging data from so I don’t want to affect them.


Try doing edit and save on the connection, and see if that resolves the problem. When this is done it will usually flush the cache. Which doesn’t happen when disabling/enabling the device. Also what version of the AB drivers are you currently using ? This can be found by going to the Modules page it will list the version number there.


Thanks for the reply. It’s useful to know that just doing Edit, Save should flush the cache.

After much frustration doing this, restarting the Allen Bradley drivers module and eventually restarting Ignition, the problem still seemed to remain. It was only then, upon looking in the PLC we saw a bug had been introduced when the program was reloaded - and what Ignition had been reading was in fact correct.

It’s still a bit worrying that reloading the PLC program caused issues to start with (aside from the non-issue above). The Allen Bradley drivers are 1.6.6 (b2014040112).

Wondering if this has been resolved, this issue seems to be constant for me.

If I am programming on a processor, go offline, do offline edits, and then download the OPC tags are wrong for a good while. Tag’s appear in folders they used to be in, and not in the folders they are now in. reading them in quick client returns a value and a “GOOD” even though the tag as it’s mapped does not exist.

I have tried editing the device. I will set the IP address wrong, save, wait 30 seconds, set it correct and save again. This used to help but currently does not (using 7.8)

This isn’t a problem in Production, but it wastes some time during development