How to Read Data With Modbus RTU

Modbus RTU Master Device connection to Modbus RTU Slave Device:

• Select “Modules” category from menu.
• Select “Driver” to connect Modbus RTU Slave Device.

• In “Drivers” page, click plus '+' button to add new driver.

• Name: Write any name you like to describe connection, for example Modbus_RTU
• Endpoint: Write port=0 or port=1 to connect Modbus Slave Device. (port=0 → Upper USB Port. port=1 → Bottom USB Port.)
• Type: Choose MODBUS RTU for connection type.
• Driver Specific Options: After choosing MODBUS RTU type for connection, default driver specific options will be appear. Set correct port, unitId and other components. If default values are correct, leave it like that.

• Then click “Save” button to establish connection.

• To see connection established, select “Status” category from menu then click “Driver” option.
• Driver name, last message and status are shown in this page, if connection is completed, green connected bar will be shown.

• After connection established, tag must be added to driver. To do that:
  • Select “Modules” from menu, then click “Tag” option.
  • In “Tags” page, click plus “+“ button to add new tag.

• “Details” page will be shown after clicked ”+” button.
• In this page:
  • Name: Choose any name you like to describe tag.
  • Type: Choose proper type for data.
  • Address: Write tag address, to use proper tag address scroll down page and look for “Modbus Tag Format”
  • Address Prefix: You can write address prefix.
  • Conversion Script: In this area, you can do mathematical operations with tag.
  • Driver Name: Choose correct Driver for Driver Name. In this example, Modbus_TCP.

• Click “Save” button to add tag.

• After adding tag, to see connection established and coming datas, select “Status” category from menu then click “Tag” option.
• In this page: Name, Last Value, Last Message, Last Update Time and Status will be shown
• If tag is added to driver successfuly, green OK message will be appear under Status.
• Last Value: Last data will be shown coming from connection.

TROUBLESHOOTING:

• If connection is not completed successfully, follow these steps to test connection:
  • Go to https://www.modbustools.com/download.html
  • Download Modbus Poll - Modbus Master Simulator
  • After setup, click and start Modbus Poll Application.

• There is connection button, click and then select connect.

• After that connection screen pop up,
• Choose Modbus Serial Port for connection type
• Set correct Serial Settings
• Click RTU Mode.
• Then click “OK” button.

• Modbus master simulator is now connected successfully to Modbus slave device.