MQTT - Publish/Subscribe

I’m trying to do some testing with MQTT, I have a Maple Systems HMI screen that is set up to publish and subscribe to topics using mqtt protocol.

I have a very simple test screen in Ignition with a single “numeric text box”. Now I do think I have all of the connection setup correct because when I input a value on the HMI 12.56(Example) the numeric text box gets updated.

My problem is when I make a change in the Numeric Text box and it tries to write back to the hmi - ignition will give me a “Write error” access denied.

I have set my security zone for the cirrus link MQTT modules to readwriteedit for all 3 modules.

Is there something simple I may be missing.


Does the HMI document that its variables are bi-directional? If not, the MQTT modules can’t override the permissions.

Yes, the hmi is enabled for “Publish/Subscribe” and I have set it up accordingly and I have tested using as my broker and it all works like it should.

I suspect I have a Iginition/MQTT-engine/transmission setting incorrect.

Would I be getting this error because Ignition is trying to write back a STRING “99” to a INT datatype?

How would I convert the “99” or even a “123.85” back to the correct datatype?


I am having the same problem. Was this ever resolved, if so, could you explain how?