> ## Documentation Index
> Fetch the complete documentation index at: https://docs.directenergypartners.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Communication

A critical step during commissioning is to verify that the controller has successfully established communication with
all devices in the microgrid. This is essential for running the application.

There are several methods to check the connection between the controller and the devices. One method is to use a tool called
**MQTT Explorer** to monitor the devices in the microgrid. The state of each device will indicate whether it is operational
or has a communication fault.

Another method is to run a **custom NATS application**. This application retrieves measurements from the controller and can
display the device ID and state of each device, providing insight into their operational state.

Both approaches are effective. For more details on using MQTT Explorer or running the custom application, refer to the
information below.

### Get Device State

To determine whether the controller has successfully connected to the devices in the microgrid, it is necessary to check
the state of each device. This can be accomplished through either MQTT Explorer or by running a custom NATS application.
Detailed instructions for retrieving the device states using both methods are provided below.

<Expandable title="MQTT Explorer">
  <Steps>
    <Step title="Download and Install MQTT Explorer">
      * **Go to the Website**: Open your browser and visit [mqtt-explorer.com](https://mqtt-explorer.com/).
      * **Download the App**: Select the version for your OS and download it.
      * **Install**: Run the downloaded file and follow the installation prompts.
    </Step>

    <Step title="Launch MQTT Explorer">
      * **Open the App**: Find MQTT Explorer in your applications and launch it.
    </Step>

    <Step title="Create a New MQTT Connection">
      * **Add a Connection**: Click the `+` button to create a new connection.
      * **Enter Details**:
        * **Name**: Give your connection a descriptive name.
        * **Protocol**: Choose `mqtt://`.
        * **Host**: Enter your controller's IP address.
        * **Port**: Set to `1883`.
        * **Leave Username/Password Blank**.
        * **Save**: Click `Save` to store the connection.
    </Step>

    <Step title="Connect to the Broker">
      * **Connect**: Select your connection from the sidebar and click `Connect`.
      * **Verify**: Confirm the connection status and check for active topics.

      <Note>
        If the MQTT Explorer application cannot establish a connection to the host (i.e., the controller), please verify the
        configuration settings in the controller's `config.json` file. You can find this file in the `/etc` folder of the
        `ppl-base` repository. Ensure that the MQTT broker is assigned the correct IP address of the controller.

        For more details, please refer to the **Configure Config File** section on the
        [Configure PPL Files](Configure%20PPL%20Files%2083ccac11bc15410994e889f37a76e999.md) page.
      </Note>

      If the connection is successful, MQTT Explorer will start listening for incoming messages. The controller will
      update the MQTT messages, including device measurements, every 5 seconds.
    </Step>

    <Step title="Check the Device’s State">
      * Select a topic from the device list on the left.
      * Choose the first (and only) entry from the dropdown menu.
      * The device measurements will appear on the right.
      * Look for the **state** parameter within the measurements.
    </Step>
  </Steps>

  <img src="https://mintlify.s3.us-west-1.amazonaws.com/directenergypartners/commission/Commission%20and%20Troubleshoot%206eca19e4112349c894b5bf8364287595/image.png" alt="image.png" />
</Expandable>

<Expandable title="Custom NATS Application">
  To run a custom NATS application, please refer to the [Write Custom Applications](Write%20Custom%20Applications%209a8ce107e094477996db591944af2dd0.md) page.
  It explains how to install the necessary libraries, update the IP address and NATS credentials, and execute the application.

  To retrieve the state of each device, run the following application found in the examples folder: `device-states.py`.
  Execute the application in the Terminal of your code editor (VS Code) using the following command:

  ```bash theme={null}
  python device-states.py
  ```

  This command will display the devices in the microgrid application along with their states.

  <img src="https://mintlify.s3.us-west-1.amazonaws.com/directenergypartners/commission/Commission%20and%20Troubleshoot%206eca19e4112349c894b5bf8364287595/image%201.png" alt="image.png" />
</Expandable>

When checking the device’s state, it is important to verify the devices that communicate over **Modbus TCP/IP**.
If the connection between the controller and the Modbus device is not established, the state will display **communicationFault**.
This indicates that the controller was unable to establish a connection, and further troubleshooting is needed.

### Resolve Communication Failure

Below are the steps to help resolve the communication failure:

<Steps>
  <Step title="Ensure the Modbus device is powered on" />

  <Step title="Verify the Modbus device is connected to the network switch">
    Verify that the Modbus device is connected to the network switch of the PPL controller using Ethernet cables.
    Check the Ethernet cable connections at both ends to ensure they are plugged in correctly.
  </Step>

  <Step title="Check the network settings on the Modbus device">
    Check the network settings on the Modbus device to ensure the IP address, subnet mask, and gateway are correctly configured.
  </Step>

  <Step title="Review the device settings in the devices.json file">
    Review the device settings in the `devices.json` file, located in the `/etc` folder in the `ppl-base` repository:

    * Ensure `ipAddress` is set correctly
    * Ensure `slaveId` is set correctly
    * Ensure `port` is set correctly

    Compare the IP address, slave ID, and port settings on the Modbus device with those in the `devices.json` file, and update them as needed.

    For more information on modifying device settings and uploading them to the controller, see the [Configure PPL Files](Configure%20PPL%20Files%2083ccac11bc15410994e889f37a76e999.md) page.
  </Step>

  <Step title="Confirm only one controller is connected to the Modbus device">
    Confirm that there is no other controller currently connected to the device (some devices only support a single Modbus client connection).
  </Step>

  <Step title="Check if the device’s address map includes a communicationCheck register">
    Check if the device’s address map includes a **communicationCheck** register. For instructions on adding Modbus registers
    to the address map, refer to the [Configure PPL Files](Configure%20PPL%20Files%2083ccac11bc15410994e889f37a76e999.md) page.
  </Step>
</Steps>

**What's next?**

<Note>
  If none of the above steps resolve the connection issue, retrieve the log files from the controller.
  Refer to the next section on how to retrieve the log files. If you need assistance, contact PPL Support by
  emailing [pplsupport@directenergypartners.com](mailto:pplsupport@directenergypartners.com).
</Note>