# General Procedure to Writeback to PLC **URL:** \ **Category:** Ignition\ **Tags:** perspective\ **Created:** [April 16, 2024, 8:07pm UTC](https://forum.inductiveautomation.com/t/general-procedure-to-writeback-to-plc/88941 "2024-04-16T20:07:23Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![Eagel007](https://avatars.discourse-cdn.com/v4/letter/e/7bcc69/32.png) [@Eagel007](https://forum.inductiveautomation.com/u/Eagel007)\ **Post date:** [April 16, 2024, 8:07pm UTC](https://forum.inductiveautomation.com/t/general-procedure-to-writeback-to-plc/88941/1 "2024-04-16T20:07:24Z")
Hi there, We currently have MQTT Architecture in place for Igntion, we utilize CMT-G01 Maple system gateways to pull read all the tags via MQTT to Ignition. I would like to experiment writing back to PLC Tags. PLC we use is AB Compact logix. I am not sure how to achieve this. Can someone please help me with step by step guide? I tried writing back to MQTT Engine tags but says read only, even if disabled all blockings. Thanks ---
**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:** [April 16, 2024, 8:17pm UTC](https://forum.inductiveautomation.com/t/general-procedure-to-writeback-to-plc/88941/2 "2024-04-16T20:17:41Z")
Are these gateways publishing to MQTT in Sparkplug format or have you used a custom namespace instead? ---
**Author:** ![Eagel007](https://avatars.discourse-cdn.com/v4/letter/e/7bcc69/32.png) [@Eagel007](https://forum.inductiveautomation.com/u/Eagel007)\ **Post date:** [April 16, 2024, 8:19pm UTC](https://forum.inductiveautomation.com/t/general-procedure-to-writeback-to-plc/88941/3 "2024-04-16T20:19:06Z")
we have a custom namespace. ---
**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:** [April 16, 2024, 8:21pm UTC](https://forum.inductiveautomation.com/t/general-procedure-to-writeback-to-plc/88941/4 "2024-04-16T20:21:01Z")
With a custom namespace tags are read only and you can only publish back to it via `system.cirruslink.engine.publish` [https://docs.chariot.io/display/CLD80/ME%3A+Python+Scripting#ME:PythonScripting-publish](https://docs.chariot.io/display/CLD80/ME%3A+Python+Scripting#ME:PythonScripting-publish) ---
**Author:** ![Eagel007](https://avatars.discourse-cdn.com/v4/letter/e/7bcc69/32.png) [@Eagel007](https://forum.inductiveautomation.com/u/Eagel007)\ **Post date:** [April 16, 2024, 8:26pm UTC](https://forum.inductiveautomation.com/t/general-procedure-to-writeback-to-plc/88941/5 "2024-04-16T20:26:13Z")
so from what I am understanding, I need to publish topic to MQTT engine and have the CMT-G01 subscribe to that topic? If so, how does CMT-G01 will write back to PLC? Will that be topic subscriber? ![image](https://us1.discourse-cdn.com/inductiveautomation/original/3X/b/e/be8fa9544d81b5588ca0dd719288900c8e056a1b.png) ---
**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:** [April 16, 2024, 8:27pm UTC](https://forum.inductiveautomation.com/t/general-procedure-to-writeback-to-plc/88941/6 "2024-04-16T20:27:06Z")
Sorry, I don't know anything about your CMT-G01 device. Presumably yes, it would need to be subscribed to the topic you published to, and have some ability to then write back to the PLC. ---
**Author:** ![Eagel007](https://avatars.discourse-cdn.com/v4/letter/e/7bcc69/32.png) [@Eagel007](https://forum.inductiveautomation.com/u/Eagel007)\ **Post date:** [April 16, 2024, 8:28pm UTC](https://forum.inductiveautomation.com/t/general-procedure-to-writeback-to-plc/88941/7 "2024-04-16T20:28:45Z")
Sounds good. I will experiment this and give review, Thank you! ---
**Author:** ![Eagel007](https://avatars.discourse-cdn.com/v4/letter/e/7bcc69/32.png) [@Eagel007](https://forum.inductiveautomation.com/u/Eagel007)\ **Post date:** [April 17, 2024, 3:26pm UTC](https://forum.inductiveautomation.com/t/general-procedure-to-writeback-to-plc/88941/8 "2024-04-17T15:26:18Z")
Great news I can see that the topic subscriber received the topic! thank you!