Relay plate R421B16 Modbus RTU

  • Hi, for the third day I am trying to make a relay board that communicates via Modbus RTU. This is my first attempt with Modbus RTU. Of course I have a map of registers but I still fail. I have read all available manuals. Can someone help me, and according to the attached document help me set up Mervis? Thank you very much.!
    0_1583338431739_modbus map.png

  • administrators

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  • administrators

    Hi @Petr-Hasoň-ml,
    can you please share what you have already done? The documentation is quite misleading and wrong at some places, but it should be possible to configure it in the Mervis.

    Best regards,

  • The point is that I can not map the registers. I have created a channel, created device (communication set up) and then a device created group. And then I want to add data points. And here I get lost, I read all available manuals from UniPi, but from the enclosed manual to the device I am not able to decipher what I should set. Such as ST Type, Offset Gap, Data Offset, Bit Offset, Multibyte Length. I play with Modbus for the first time and have been playing with it for 4 days and no progress. So I go for advice. Thanks a lot for any help.

  • Hi
    i have it like this (about the same relay board).
    I don't know if it's good, but it works.


  • @tomas
    Hi, thank you very much for your great tutorial. The board lives, and works well. I start to understand how to work with addresses. Previously I made the mistake of creating one group and trying to express all the relays with data points. Now I know it was nonsense. Thanks again very much. :-)

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