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unit ID in modbus TCP slave device

  • mmxfan

    mmxfan - 2020-11-05

    Why I cannot find the unit ID on "Tab β€˜ModbusTCP Slave Device - General’"? Is it because I'm using the latest version of the modbus TCP slave library? Without unit ID setting available, I have to set device ID to 255 when using modscan or other test softwares. Or is there any to ignore the unit ID for the modbus TCP slave device?

  • thebushyone

    thebushyone - 2020-12-18

    Hi mmxfan, Did you find a solution as I have the exact same problem with the removal of the unit ID

    • mmxfan

      mmxfan - 2021-01-07

      not a chance.

  • i-campbell

    i-campbell - 2021-01-07

    With SP17 (March 2021 maybe?) the modbus TCP slave device will ignore the unit-ID, if a serial gateway is not enabled. So you will be able to use any unit-id you like. Currently Unit-ID 0 (really a broadcast to all addresses) and Unit-ID 255 work.

    I am curious, do you have some modbus-master device, which cannot use unit-id 0 nor 255?

  • thebushyone

    thebushyone - 2021-01-07

    Sorry, should have posted. The issue ended up being that in Modbus TCP Slave I/O Mapping I had to change the Bus Cycle Task to "Task" and the Always Update Variables to "Enabled 2 (always in bus cycle task)". Everything kick in at that point


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