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Insufficient data received error in modbus

Discussion in 'General Electronics Discussion' started by paddy, Jul 24, 2014.

  1. paddy

    paddy

    81
    0
    Sep 11, 2012
    Hi,

    I have a monitor which is programmed as modbus slave (RTU).

    When I am connecting single device and checking the RS485 communication using Modbus poll and RS232 to RS 485 converter, it works fine. But when I connect another similar device in loop at that time it gives insufficient data byte error and CRC error.

    For single device there is no problem but it gives error when I add another device. Please find attached text file.

    Please advice what could be the problem.

    Thanks,
    Paddy
     

    Attached Files:

    Last edited: Jul 24, 2014
  2. paddy

    paddy

    81
    0
    Sep 11, 2012
    Hi,
    The problem was occurring because of improper voltage (reverse voltage i.e. VCC is connected to GND and vice versa) to bias resistors.

    Regards,
    Paddy
     
  3. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
    1,266
    Nov 28, 2011
    Thanks for following up here.

    So that error meant that when a device stopped driving the RS-485 bus, it would be pulled into a break state? And that causes the Master to report "insufficient data" and a CRC error?
     
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