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DeviceBridge - Implementing Read/Write Communication Between DataLayer and MQTT

DeviceBridge - Implementing Read/Write Communication Between DataLayer and MQTT

Established Member


I'm attempting to implement the following scenario on CtrlX Virtual.

I have created a datalayer tag, for example, "var1," and the path looks like "samples/kvd/implicit_one_level/var1" cause I'm using KVD (Key Value Database App). Operations read and write are allowed.

Next, DeviceBridge publishes this variable (Datalayer device) to the MQTT Broker (Connector) through simple JSON Collector. The Datalayer tag publishes well.

However, bi-directional communication is required, so I've enabled the WriteBack function. Unfortunately, nothing seems to be happening.

Is it possible to set up communication in both directions between the Datalayer and MQTT?

Any insights or suggestions would be greatly appreciated.



Hi @Ievhen ,

What is the second direction of communication in your case? The MQTT broker writing back to the datalayer?

You've enabled WriteBack function, but have you set up any writeback tags? The current function only allows write back within the Device Bridge collector logic and does not handle direct write operations to the Device Bridge write back datalayer endpoint.

This video might help you out.

Established Member

Thank you for your response.
Exactly, the second direction of communication in my case involves the MQTT broker writing back to the datalayer.

In attempting to implement this, I set a second variable in kvd, for instance, var2, on the same device to store the received back value. However, I encountered the following error:  >  : Endpoint var2 is readonlyScreenshots attached.

I might be missing a crucial step

Unfortunately, this is a limitation of Device Bridge. I believe you will require a two device license in this case, as the datalayer counts as a device. I've requested an update to the app to allow writeback to the datalayer as a standard function on a single device license.

Here is a document describing how to do this with an AB PLC, but the process should be the same.