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DoMore and BRX reloading due to modbus TCP request. !LOL (not LOL)

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  • DoMore and BRX reloading due to modbus TCP request. !LOL (not LOL)

    Hi. Long story short but when i make a request to read 200 holding registers - PLC reloading. Tried to increase watchdog timeout - no luck. Tried to do the same with BRX - it is reloading after received request. Played with PAC - it does not respond, but at least continue to work properly...

  • #2
    There was a bug in the Do-more Modbus/TCP server implementation where an invalid request would result in a buffer overrun. It has been fixed, but not shipped (should be later this month). Pretty sure the maximum valid number of holding registers in a single request is 125.


    • #3
      Looks like BobO is correct about number of registers per request.
      In Do-More Designer 2.3, the MRX (Modbus Read instruction) throws an error message when trying to have it read more that 125 registers:
      ... P7 Number of Modbus Discrete Inputs Too many registers for Modbus Function Code 4 (175); valid range is 1 to 125 ...


      • #4
        Its not about DoMore request. The invalid request should be sent from another device or even application to DoMore PLC, and only in this case (so far) you will see "funny result".