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Meaning of flush error received from mod-bus slave

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  1. Mar 13, 2017 #1
    I have a PC(as master) and a compressor(as slave) in modbus communication. I am using 1000ft cable and I want to analyze the interference effect on the data communication error. I am coupling burst signals produced by the relay switching and I could observe the level of burst to be ~50V. When I am coupling this bursts I am getting error messages from slave. The type of error is 'FLUSH'. I need to know what is mean by the flush error err.PNG
     
  2. jcsd
  3. Mar 13, 2017 #2

    anorlunda

    Staff: Mentor

    Wow. I can only guess. Could it be that a buffer got full and the contents were flushed before resuming?

    I think the only one who can tell you for sure is the software's author.
     
  4. Mar 13, 2017 #3

    berkeman

    User Avatar

    Staff: Mentor

    I don't see anything about Flush in the Exception Codes at the wikipedia page about Modbus:

    https://en.wikipedia.org/wiki/Modbus

    What is your physical layer? Doubly-terminated RS-485? How are you coupling the noise into the cable? What cable are you using, and what value of termination resistors are you using?
     
  5. Mar 13, 2017 #4

    anorlunda

    Staff: Mentor

  6. Mar 14, 2017 #5
    I already saw this, but this function is defined if developers are using libmodbus library right? Will that error description be same even if libmodbus library being not used? I didnt see such error definition in modbus.org
     
  7. Mar 14, 2017 #6
    So what do you think, can I correct this error by modifying via software means? I mean with the help of developers?
     
    Last edited by a moderator: Mar 14, 2017
  8. Mar 14, 2017 #7

    anorlunda

    Staff: Mentor

    I think your evidence is too weak to guess at a remedy. You need to investigate more to find the cause.

    Have you contacted the manufacturer?
     
    Last edited by a moderator: Mar 14, 2017
  9. Mar 14, 2017 #8
    I am new to this area, what kind of investigation you are suggesting to find the cause? I am not getting the idea
     
  10. Mar 14, 2017 #9

    anorlunda

    Staff: Mentor

    You need to find the people who wrote that "FLUSH" error message and ask them what kinds of things could cause that.

    That sounds pretty ambitious for a newcomer.

    It could be "the interference effect on the data communication" is to cause FLUSH errors. :smile:

    Seriously, the interference could cause data communication errors which means retries, which causes buffer overflow, which triggers FLUSH. To accomplish the research that you described implies pushing things to the margins. I would think that you need to know everything about the hardware and software, even to the extent of writing all the software yourself. Otherwise, how will you tell the difference between anomalies your research is seeking and faulty equipment?
     
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