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"Modbus_RTU" library - Start Address for each function.

ktakedaktakeda
edited October 2021 in PLCnext Store
I'm now confusing about uiStartAddress for "Modbus_RTU" library.
The document says as followings;
- uiStartAddress, UINT, The input specifies the start address of the bit to be read on the slave.
And, for "Example 1: Modbus_RTU AXL master functionality" , uiStartAddress is 3000 for MB_RTU_FC1.
Why uiStartAddress is 3000 for MB_RTU_FC1 ? What means about 3000 ?
I'd like to know the start address for each function of MB_RTU_FC1, FC2, FC3, FC4, FC5, FC6, FC15, FC16, FC23.

Comments

  • Martin [PLCnext Technology Team]Martin [PLCnext Technology Team]
    Fo others with the same problem, here is the solution from the author of the original post:
    I set starting address (uiStartAddress) to "0", so that I could communicate with other device.
  • HayderMohammedHayderMohammed
    Hello,

    I am trying to use ModBus RTU RS485 to send data to Modbus Slave software. The setting and the address are correct. But I getting an error 16#C020, 16#0010.
    (16#C020: Error when sending.
    16#0010 :Process data timeout during the send process between PLC and module)

    I have AXC F2152, RS UNI 2688666), I have tried different libraries 10, 12 and all giving me the same error. Please, is there any solution for this problem?

    Thanks in advance
    Hayder
  • Martin [PLCnext Technology Team]Martin [PLCnext Technology Team]
    There may be a problem with the wiring between the RS UNI module and the device, or with the remote device itself, or with the hardware configuration of the PLCnext Engineer project, or with the settings on the RS UNI module, or with the Process Data connections to the RS UNI module, or with the configuration of the Modbus TCP function blocks in the project, or ... maybe something else.

    Someone would need to go through all those details with you, to identify the source of the problem.

    Someone in the Phoenix Contact office in your country should be able to work through the application with you and help identify the problem, if you want to call them. Otherwise, we can send you an email (to the address you used to register on this Forum) and get all the details from you that way, if you prefer.
  • HayderMohammedHayderMohammed
    Dear Martin, thanks for your reply.

    I already have the same module and the same configuration and the same wiring and same programming in another panel and It works with a VFD perfectly.

    Then, I have used the same RS module in PLCnext starter kit at home and simulate a Slave in Modbus slave software and I have got this problem.
    Do you see any problem in my setup?

    Thanks in advance

    Hayder
  • Martin [PLCnext Technology Team]Martin [PLCnext Technology Team]
    edited February 2022
    If the only thing that is different from the working system is the Modbus TCP device, then that's what I would check first.
    What Modbus Slave software is being used?
    What device is the Modbus Slave software running on?
    Is there a data sheet for the RS422/485 port on the Modbus Slave device, showing the pin assignments?
    What specific pins are wired between the Modbus Slave device and the RS UNI module?

    Just to be clear, when you say "Modbus Slave", you mean "Modbus Server", right?
  • HayderMohammedHayderMohammed
    Hi Martin,

    In my PLCnext engineer I have used Modbus RTU 485 and I am Master and I have used modbus RTU master block from PlcNext library.
    And, I have used Modbus Slave simulator from Modbus tools (modbus tools For test, simulation and programming) You can find it on their website.

    For the wiring I am using Modbus RTU RS485 to USB adapter to connect RS uni module to my computer.
    The adapter I order it online. Adapter name: MAX485 module voor RS485 seriële communicatie USB.

    In the modbus slave program I only give the basic parameters such Baud rate, parity, 8Dbits and Address.

    But the error code that I got shows an error in the PLC not in the communication or not in the transferred date.

    Last Note: In my Plcnext starter kit I see led (D) flashing green in the AI/AO and RS Uni module. Does that give you an indication?

    Thanks
  • Martin [PLCnext Technology Team]Martin [PLCnext Technology Team]
    I see led (D) flashing green in the AI/AO and RS Uni module. Does that give you an indication?
    According to the data sheet for the RS UNI, that means no process data has been transferred to the RS UNI module from the PLC over the Axioline bus.

    Can you confirm that the I/O modules in the PLCnext Engineer project are exactly the same as the actual I/O modules connected to the PLC? (i.e. part number and installation order, from left to right)

    Can you confirm that, in the PLCnext Engineer project, you have the two Process Data port variables on the RS UNI (~DI160 and ~DO160) connected to corresponding IN and OUT Port variables of type MB2_AXL_RSUNI2_ARR_B_0_19 ?

    Can you confirm that those IN and OUT Port variables, the ones connected to the ~DI160 and ~DO160 ports on the RS UNI, are the same ones being using as parameters on the RTU Master function block?
  • HayderMohammedHayderMohammed
    Hello Martin,

    Thanks a lot for your reply.

    Yes, You are right I have forgotten to link RS Uni ports to In/Out array. Now, I have it without any error.
    Tomorrow, I will try the communication with LabView.
    I will let you know about the result.

    Many thanks for your help and support.

    Hayder
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