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Problems with PC to PLC communication, using Modbus

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  • JorgeL&C
    replied
    Originally posted by kewakl View Post

    You do need to assign the P2k Tag's Modbus addresses in the P2K tag database.

    It just worked for me, I think that of that last thing you are talking about I had already done it. What was wrong was the arrangements were poorly declared, had not assigned value to Columns and another detail is that within the PLC 1 is added to the Starting Address. Then I will post the corrections so others can use it.

    Thank you, kewkl.

    Leave a comment:


  • kewakl
    replied
    Originally posted by JorgeL&C View Post
    Thanks OpZed for answering me. I ask you why it is the first time I work with this PLC, What I show in the images on the PLC side, is not exactly what you suggest to me?



    In other words, I think I have assigned an address in the TagDB, or is it something else?
    You do need to assign the P2k Tag's Modbus addresses in the P2K tag database.

    Leave a comment:


  • JorgeL&C
    replied
    Yes, I think the array is badly declared.

    Leave a comment:


  • JorgeL&C
    replied
    Thanks OpZed for answering me. I ask you why it is the first time I work with this PLC, What I show in the images on the PLC side, is not exactly what you suggest to me?

    Originally posted by OpZed View Post
    By default the P-series allows reading any address, but if the address isn't assigned in the TagDB it will just return zero as the data. Writes must be to assigned addresses. Try writing a size of 1 and then increment the address until you get the data alignment that you expect.
    In other words, I think I have assigned an address in the TagDB, or is it something else?

    Leave a comment:


  • JorgeL&C
    replied
    Thanks kewakl for answering me. Certainly, MODBUS does not know what the absolute address of the register/coil is, the Starting Address that MODBUS uses is relative, it is within the PLC where that Starting Address, that receives from the MODBUS, which address register / coils to affect is internally linked.

    For the examples, I set both for register and for coils, the addresses are correct because the salve MODBUS of the PLC works well when required to read the registers/coils. I have the impression that within the PLC, I need to put some parameter, which I don't know, in order to alter the registers/coils information of an Array, through the slave MODBUS. Which?

    Leave a comment:


  • OpZed
    replied
    By default the P-series allows reading any address, but if the address isn't assigned in the TagDB it will just return zero as the data. Writes must be to assigned addresses. Try writing a size of 1 and then increment the address until you get the data alignment that you expect.

    Leave a comment:


  • kewakl
    replied
    Modbus exception code 2 is illegal data address. Verify the register/coil addresses are correct.
    Sometimes, you may have to subtract '1' from these addresses [in the LSIS (?) software ]- depending on the manufacturer's/developer's whims.
    Which port are you using on the P2K. You may have to swap the (rx/tx ; D+/D-; A/B) wires.

    Leave a comment:


  • JorgeL&C
    started a topic Problems with PC to PLC communication, using Modbus

    Problems with PC to PLC communication, using Modbus

    Hello, it's my first post and my english is poor. This way of communicating with the PLCs is already usual, even before I had already achieved it with AUTAMATION DIRECT, but this time they changed the software, which I think for the best, however I cannot send the information from the PC to the PLC, as you will see in the images. What am I missing?

    Thank you.


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