Configuration of Connection Parameters

After you have prepared the Event Grid as well as the CODESYS project, you can parameterize the connection and establish the connection to the broker.

Adding a thumbprint to the client identity

The thumbprint of the device certificate which was read in the Reading a thumbprint chapter must be specified as the primary thumbprint for the created client identity.

To do this, navigate to the client overview in the Azure portal and click the matching client identity.
The properties form is similar to the form used when creating the MQTT client.
In the Primary Thumbprint field, set the thumbprint and click the Save button to save the changes.

Starting the sample project

Download the example application to the controller and start it.
The following visualization opens.

Establishing a connection between the MQTT client and the broker

In the Connection Settings area, specify your connection parameters:

Parameter	Value	Description
Server / IP / URL	<MQTT Hostname>	The MQTT hostname you used in the TLS context.
Server Port	8883	For secure MQTT communication, Port 8883 is used by default and is therefore expected by the Event Grid Broker.
Use TLS	True	The Use TLS check box must be selected (checked) in order for the configured TLS context to be used. Important This check box has nothing to do with the deprecated flag `xUseTLS` of the `MQTTClient` function block. This flag should no longer be used.
Username	my-auth-name	The authentication name which was specified when the client identity was created must be specified in the `Username` field. In the case of the example, it is `my-auth-name`. For more information, see Creating an MQTT client corresponding part in section 2.4.
Client Id	MyClient1	Any name

In the Last Will Settings area, use the Connect to Broker switch to activate the MQTTClient function block.
The lamp underneath turns green as soon as the client is connected to the broker.

Testing the communication

To test the communication, the client should send a message to a topic and receive the sent message back.

Setting up a subscriber

In the Subscriber 1 area of the visualization, specify the following parameters:

Parameter	Value	Description
Topic Filter	`permitted/#`	Receives all messages whose topic root is `permitted`. When creating a `Spaces` topic, the topic template `permitted/#` was used, on the basis of which the permissions were granted. If a topic used here which does not begin with the root `permitted`, then the client does not have permission to subscribe to this channel, which in turn results in an error state. For more information, see the following: Creating a topic space and Definition of permissions

Parameter

Value

Description

Topic Filter

permitted/#

Receives all messages whose topic root is permitted.

When creating a Spaces topic, the topic template permitted/# was used, on the basis of which the permissions were granted. If a topic used here which does not begin with the root permitted, then the client does not have permission to subscribe to this channel, which in turn results in an error state.

For more information, see the following: Creating a topic space and Definition of permissions

Use the Subscribe switch to activate the MQTTSubscribe function block.
The lamp underneath turns green, as when establishing a connection to the broker, if the action has been successfully completed.

Setting up a publisher

In the Publisher 1 area, specify the following parameters in the visualization:

Parameter	Value	Description
Topic	`permitted/test`	Sends a message on the topic/channel `permitted/test`. Because the subscriber listens to all channels below the permitted root, it will receive this message. When creating a `topic space`, the topic template `permitted/#` was used, on the basis of which the permissions were granted. If a topic used here which does not begin with the root `permitted`, then the client does not have permission to publish/send anything to this channel, which in turn results in an error state. For more information, see the following: Creating a topic space and Definition of permissions
Message	<text>	Any message to be sent.

Parameter

Value

Description

Topic

permitted/test

Sends a message on the topic/channel permitted/test. Because the subscriber listens to all channels below the permitted root, it will receive this message.

When creating a topic space, the topic template permitted/# was used, on the basis of which the permissions were granted. If a topic used here which does not begin with the root permitted, then the client does not have permission to publish/send anything to this channel, which in turn results in an error state.

For more information, see the following: Creating a topic space and Definition of permissions

Message

<text>

Any message to be sent.

Starting a data transfer and receiving data

In the Publisher 1 area of the visualization, click the large Publish button to send the defined message on the topic "permitted/test".
In the Subscriber 1 area, you should now be able to see the sent message and the topic on which it was received.

The CODESYS MQTTClient communicates successfully via the MQTT broker of the Azure Event Grid namespace.

In this section: