Laura -
I have been working through similar issues with v21. As Kevin mentioned, the “external access” setting was a problem for me, among some others that tech support is working on. If I understand correctly, the driver is reading the entire UDT, and it will assign the strictest policy it finds to the entire UDT tag structure, apparently it’s an optimization thing. If you have a single tag set to “none”, the entire UDT will fail. Right now I’m also having issues writing to tags, and am wondering if it is applying a “read only” status to all tags if a single tag is marked as “read only”.
That could be a problem as there are default tags created for an Add On Instruction that are fixed as “read only”. Waiting to hear back from tech support. Also, parameters of an AOI defined as InOut don’t have external access directly, I assume the inherited external access settings are accounted for, but waiting for confirmation from tech support.
Personally I see this as a big problem as Add On Instructions can be locked down. If you are using an AOI that cannot be changed, well you’re pretty much out of luck. I have a proprietary AOI in my application, and while it isn’t locked down I’m hesitant to changing anything in the AOI.
For those who are upgrading an existing application, the OPC path has changed. So if you have defined UDT’s you will have to re-work all of that.
I am starting to evaluate Kepware as an alternative.