# Cannot read some tags inside Rockwell AOI **URL:** \ **Category:** Ignition Early Access\ **Created:** [September 4, 2020, 11:09am UTC](https://forum.inductiveautomation.com/t/cannot-read-some-tags-inside-rockwell-aoi/38393 "2020-09-04T11:09:49Z")\ **Posts on this page:** 1\ **Showing post:** 24
**Author:** ![pturmel](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/pturmel/32/3295_2.png) [@pturmel](https://forum.inductiveautomation.com/u/pturmel)\ **Post date:** [December 5, 2020, 7:50pm UTC](https://forum.inductiveautomation.com/t/cannot-read-some-tags-inside-rockwell-aoi/38393/24 "2020-12-05T19:50:10Z")
Well, I usually use _three_ UDTs for my AOIs. The AOI gets the base name (`xyz`, perhaps) for its functionality. The others: - `xyz_fbk` This is the collection of values that present the process variables, indicators, trigger integers, etc. Subscribed in Ignition with a fast pace, or mapped through my E/IP module from a PLC output buffer. - `xyz_cmd` This is the collection of setpoints and command bits and handshake short integers. Subscribed as needed (slow/leased is fine), but usually mapped to a PLC input buffer with E/IP. If so, can contain momentary buttons driven from my custom component. - `xyz_cfg` This is the collection of configuration items for the AOI, like process/alarm limits, tuning constants, operating modes, etc. Subscribed slow in a leased scan class, so the traffic is only present when the user has the corresponding configuration UI open. Note that Ignition never writes into the `xyz_fbk` data, and the PLC never writes to `xyz_cmd`. This is crucial to avoid race conditions. And it fits well with E/IP I/O configurations. --- _[View the full topic](https://forum.inductiveautomation.com/t/cannot-read-some-tags-inside-rockwell-aoi/38393)._