MQTT I/O Item Name

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MQTT IOItemName Introduction

When I/O Data Point Tags are associated with an MQTT Connection Tag, the IOItemName property defines:

The remainder of this page describes:

MQTT IOItemName Editor

Use the MQTT I/O Item Name Editor Dialog to edit the IOItemName field of I/O Data Point Tags:

MQTT Topic Name Editor

To open MQTT I/O Item Name Editor Dialog, click the Browse button Browse button of the IOItemName property.

MQTT IOItemName Format

The syntax of an MQTT IOItemName is:

IO-Item-Name ::=
    Read-Topic-Name [ '#' text-selector ][ ';' Write-Topic-Name ]



  1. Simple Mapping with No Transformation

    This example maps an I/O Data Tag to a topic with no transformation:


    The driver subscribes to the topic 'Home/Basement/Light1'. Values published by the MQTT Broker using this topic name update the value of the tag. The entire value of the topic is used. Write requests from Fernhill SCADA are published to the same topic name 'Home/Basement/Light1'.

  2. Mapping with a JSONata Read Transformation

    This example shows a read topic, a JSONata read selector, and a write topic:


    The topic is assumed to have the following structure:

    { "Light1" : false,
      "Light2" : true,
      "Light3" : false }

    The driver subscribes to the topic 'Home/Basement/Lights'. The value of the Light3 element is used to update the tag value. Write requests from Fernhill SCADA are published to 'Home/Basement/Lights/Light3'.

Further Information


To learn more about the lightweight JSON transformation language.

Fernhill SCADA Drivers

For information about other drivers available in Fernhill SCADA.


For the meaning of terms used in Fernhill SCADA.