modbus Response

Discussion in 'Programmer's Corner' started by btb4198, Jul 8, 2013.

  1. btb4198

    Thread Starter New Member

    Jul 8, 2013
    6
    0
    when writing a Response in modbus
    what are the
    Byte Count and Register Values used for ?

    now I think the Register Values is the value I was so sent over modbus
    is this right?
    how many bytes can it be ?
    and how many Bytes are byte count?
     
  2. RRITESH KAKKAR

    Senior Member

    Jun 29, 2010
    2,831
    89
    Are you using a home made PLC??
     
  3. WBahn

    Moderator

    Mar 31, 2012
    17,737
    4,789
    At least go out and read the Wikipedia article on Modbus and try to look at some of the references it provides. Then come back and try to ask more detailed and specific questions and include such things as what frame format you are using.
     
  4. btb4198

    Thread Starter New Member

    Jul 8, 2013
    6
    0
    I am using a honeywell experion server and I have looked up Modbus alot. My Response is not working and I do not know why. ok i am getting this from experion now
    8 bytes
    1 3 78 32 0 1 146 232 experion kepts getting an error everytime it output a message.

    I am sending back this
    7= bytes
    1 3 2 0 4 146 232
    Slave address = 1
    Function code = 3
    bytes count = 2
    high bytes data = 0
    low bytes data = 4
    high crc = 146
    low crc = 232

    so what is wrong with my Response ?
     
  5. WBahn

    Moderator

    Mar 31, 2012
    17,737
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    Are you really expecting someone to figure out what the error is with your server based on this?

    Good luck.
     
  6. btb4198

    Thread Starter New Member

    Jul 8, 2013
    6
    0
    what more information do you need? I do not know what the error is because experion does not say.
     
  7. MrChips

    Moderator

    Oct 2, 2009
    12,440
    3,360
    How come the CRC is the same for both messages?
    Is that a coincidence?
     
  8. WBahn

    Moderator

    Mar 31, 2012
    17,737
    4,789
    And so we are supposed to know what is supposed to happen if you tell it to use function code 3 with slave address 1?

    How are you computing your CRC values?
     
    btb4198 likes this.
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