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Modbus TCP Link

Read and write coils and registers on a network device.

Coils and registers, through Connection Service, to Mapped tags in the project.Coils and registersConnection ServiceMapped tags

Set it up

  1. Start the Connection Service. Stop the PLC and add a Modbus TCP Link from I/O Links.
  2. Enter the device address, port and unit identifier on Connection. Use a device on a private network you are allowed to use.
  3. Connect, then add the coils or registers you need. Match the function, address, direction and data type to the device documentation.
  4. Watch a known input value before adding any output mapping. Check the displayed connection status and diagnostics.
  5. Run the project. Use a controlled training setup when testing writes.

Check before you run

  • Tag rows use short names within their device scope. The full reference is IO::Link.Device.Tag; short references require an explicit saved alias.
  • Device IDs are assigned when you save the Link. A tag’s scope prefix is IO::Link.Device; labels are display text, while symbols identify that scope in references.
  • Modbus uses zero-based offsets and network byte order. Range metadata validates values; it does not scale them.
  • A register number printed in a device manual may use a different address base. Confirm it before mapping several values.
  • Two registers used for one value must use the device’s word order. A connected status alone does not prove the value is decoded correctly.
  • A timeout is a failed read, not a new zero measurement. Check diagnostics and the connection before trusting an old value.

If it will not connect

Check the Connection Service indicator, the device or server address, and the Link’s diagnostics. A saved mapping does not mean the device is connected. Stop the PLC before changing the Link.

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