MQTT I/O Item Name

Help Contents

MQTT IOItemName Introduction

When I/O Data 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 Tags:

MQTT Topic Name Editor

To open MQTT I/O Item Name Editor Dialog, click the Browse button Browse button at the right side of the IOItemName field.

MQTT IOItemName Format

The syntax of an MQTT IOItemName is:

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

Where:

Read Transform

The Read-Transform uses this syntax:

Read-Transform ::=
    { JSON-Read-Transform | CSV-Read-Transform }

JSON-Read-Transform ::=
    'JSONata(' JSONata-Expr ')'

CSV-Read-Transform ::=
    'CSV(' Cell-Reference ')'

Where:

Examples

Simple Mapping with No Transformation

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

Home/Basement/Light1

The driver subscribes to the topic 'Home/Basement/Light1'. Values published by the MQTT server 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'.

Mapping with a JSONata Read Transformation

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

Home/Basement/Lights#JSONata(Light3);Home/Basement/Lights/Light3

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

JSONata

To learn more about the lightweight Java Script Object Notation (JSON) transformation language.

Fernhill SCADA Drivers

For information about other drivers available in Fernhill SCADA.

Glossary

For the meaning of terms used in Fernhill SCADA.