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Sample Modbus Message

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  • Sample Modbus Message

    Hi all,
    I have been playing with modbus - with little success I might add.

    Could some one give me an example message for a DL05 OR verify that the one I have ben trying to send is correct.

    Slave id: 17

    Function Code: Force Single register

    Register address: c173 (Octal DL05 addressing)

    Data: FF00

    CRC: 00FF

    message: 0x11 0x05 0x0C 0x7C 0xFF 0x00 0xFF 0x00

    I am simply trying to force a coil that will set Y0 on.

    Thank you all!!
    Happy new year


  • #2
    Your example looks strangely familiar with one shown at the "Simply Modbus" site. Is the CRC correct?

    This is what I got with their software in demo mode:

    11 05 0C 7B 00 01 7D D3
    Last edited by bcarlton; 12-31-2010, 03:22 PM.



    • #3
      Thank you and happy new year!

      I down loaded the Modicon Modbus Protocol Reference Guide, I forget where. I tried to follow the examples as closely as I could.

      I have been to simply modbus - and evidently my CRC is not correct.

      Thank you, I will try your message.

      I thought that it would spit back a bad crc code if that was the only thing wrong.



      • #4

        My DL05 keeps spitting back an 0x02 - Illegal address exception.

        I tried to initialize the scratch pad, but it still gave the same error. It is an older PLC, I suppose that there is a chance that the PLC itself is bad.

        in the C-More help file they have a nice chart of 05, 06, 260 modbus addresing. Even when I use the base address for say coils, I get an illegal address.

        I wonder if I can update the firmware??? I will try that and get back to you.


        P.S. I liked your suggestions to the cell phone companies, but there is little chance of that happening. They want to keep you over a barrel.


        • #5

          I updated the Firmware from 2.20 to 5.30. I am still getting an illegal address with function code 5. It will read coils and registers, it just won't allow me to write to them.

          Unless there is a secret magic box to check somewhere, I am going to have to write this off as equipment failure until I can get my hands on some newer hardware. I am at a loss on this.


          Thank you for your help.


          • #6
            My Modbus applications have always been from the PLC out to devices. You seems to have stuff correct and according to the DL05 manual Function 05 should work with the C bits.

            Regarding the wireless companies, I know it's only a pipe dream. But business models built on deception are despicable in my eyes, 'fine print' literally being the essence of 'hidden' to my aging eyes. DIRECT TV just go slapped for their version of it.



            • #7
              Is your mode switch in TERM?


              • #8

                0x01 0x05 0x0C 0x7B 0xFF 0x00 0xFF 0x73

                Some how the message at simply modbus were off. I couldn't figure out how to fix it without figuring out how to calculate the CRC. Once I figured that out, well I got it.

                This should turn coil 173 on in slave 1 for any of the DL205 family.

                Thank you all!!