# Cannot read some tags inside Rockwell AOI

**URL:** <https://forum.inductiveautomation.com/t/cannot-read-some-tags-inside-rockwell-aoi/38393>\
**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:** 85

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**Author:** ![Kevin.Herron](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/kevin.herron/32/7259_2.png) [@Kevin.Herron](https://forum.inductiveautomation.com/u/Kevin.Herron)\
**Post date:** [February 18, 2025, 11:49pm UTC](https://forum.inductiveautomation.com/t/cannot-read-some-tags-inside-rockwell-aoi/38393/85 "2025-02-18T23:49:22Z")

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> [@nminchin](#):
>
> SCADA writes to the tag setting it True, the PLC immediately resets it to False, but SCADA remains True indefinitely.

This is a race condition that can happen if you use the "Read After Write" option in tag groups with an OPC UA subscription. Not sure about other causes.

> [@Indirect Tag Delay](https://forum.inductiveautomation.com/t/indirect-tag-delay/28734/9):
>
> Imagine, if you will, a boolean tag in a 30 second scan class.
> 
> 1. driver polls value=`false`, next poll in 30s
> 2. user writes value=`true` to tag, read-after-write confirms value=`true`, ignition tag now set to true
> 3. some seconds later, before the next poll, an external source (script, PLC logic, whatever) sets the value to `false` again
> 4. driver eventually polls again, reads value=`false`, no change since last poll, so no data change is sent to client
> 
> The tag is now false in the PLC but true in Ignition.

from [Indirect Tag Delay - #9 by Kevin.Herron](https://forum.inductiveautomation.com/t/indirect-tag-delay/28734/9)

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