# Ignition Does not reflect PLC value change **URL:** \ **Category:** Ignition\ **Tags:** perspective\ **Created:** [February 25, 2025, 2:30am UTC](https://forum.inductiveautomation.com/t/ignition-does-not-reflect-plc-value-change/102831 "2025-02-25T02:30:00Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![Dean\_Venter](https://avatars.discourse-cdn.com/v4/letter/d/b782af/32.png) [@Dean\_Venter](https://forum.inductiveautomation.com/u/Dean_Venter)\ **Post date:** [February 25, 2025, 2:30am UTC](https://forum.inductiveautomation.com/t/ignition-does-not-reflect-plc-value-change/102831/1 "2025-02-25T02:30:01Z")
Hi All, I have a problem that I just cant seem to solve. I have a Rockwell PLC where I have AOI's to create control modules. In order to change the modes in the control modules, I use a common command in which different command values would make different mode changes in the PLC. In order to reset the command, at the end of the scan, the command value is set to 0 in the PLC. My on click script in the SCADA sets the value correctly in the PLC and the right mode change is executed, however, when the PLC sets the command to 0 at the end of the scan, the SCADA does not update accordingly. The only way to update correctly is to restart the tag in Designer or to manually change the command value in the PLC to a non zero number which seems to prompt the SCADA to update correctly. Have played with deadband values and modes with no luck. Its almost as if the command is changed in the PLC to quickly or the SCADA simply does not poll the PLC until a value change is registered. Putting a delay in the value in the PLC before resetting the value makes it work but also makes the SCADA feel slow. Any help or tips would be greatly appreciated. ---
**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 25, 2025, 3:53am UTC](https://forum.inductiveautomation.com/t/ignition-does-not-reflect-plc-value-change/102831/2 "2025-02-25T03:53:41Z")
Do you have this tag in a Tag Group in which you’ve enabled “Read After Write”? ---
**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:** [February 25, 2025, 1:15pm UTC](https://forum.inductiveautomation.com/t/ignition-does-not-reflect-plc-value-change/102831/3 "2025-02-25T13:15:21Z")
Consider using `system.opc.writeValue()` to set such signals, bypassing the tag system. ---
**Author:** ![jlandwerlen](https://avatars.discourse-cdn.com/v4/letter/j/bc8723/32.png) [@jlandwerlen](https://forum.inductiveautomation.com/u/jlandwerlen)\ **Post date:** [February 25, 2025, 1:21pm UTC](https://forum.inductiveautomation.com/t/ignition-does-not-reflect-plc-value-change/102831/4 "2025-02-25T13:21:44Z")
This was a recent topic of conversation: > [@Cannot read some tags inside Rockwell AOI](https://forum.inductiveautomation.com/t/cannot-read-some-tags-inside-rockwell-aoi/38393/71): > > Hey Phil, I'm a bit embarrassed to ask, but how in Perspective do you recommend issuing commands from SCADA to xyz\_cmd registers, and having them reset themselves from SCADA (without PLC writing to them) so as to avoid race conditions? This still confuses me.. would you suggest tag value change scripts to do this resetting? ---
**Author:** ![Dean\_Venter](https://avatars.discourse-cdn.com/v4/letter/d/b782af/32.png) [@Dean\_Venter](https://forum.inductiveautomation.com/u/Dean_Venter)\ **Post date:** [February 25, 2025, 11:41pm UTC](https://forum.inductiveautomation.com/t/ignition-does-not-reflect-plc-value-change/102831/5 "2025-02-25T23:41:41Z")
Hi Kevin, It worked perfectly! I made a new tag group to "Read After Write" which is only used by the command tags I am using to reduce load. Thank you very much for the help. ---
**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 25, 2025, 11:42pm UTC](https://forum.inductiveautomation.com/t/ignition-does-not-reflect-plc-value-change/102831/6 "2025-02-25T23:42:32Z")
You should only use Read After Write if you're also using OPC Polled/Read mode for that Tag Group! It's dangerous otherwise.