Thread: COM Port not accepting "11" bytes

  1. #1
    Registered User
    Join Date
    Jul 2008

    COM Port not accepting "11" bytes

    Hello, I 've been working on some code that requires me to output a stream of byte through a COM port. Everything works fine until I have to output a value that corresponds to the byte "11." In that case, it doesn't output anything at all. Not a zero, not a randomized byte, it just skips right over it. Does anyone have a clue why this happens?

    P.S. It seems to be due to the WriteFile function found in the winbase.h file.

  2. #2
    Kernel hacker
    Join Date
    Jul 2007
    Farncombe, Surrey, England
    Is that 11 decimal or 11 hex?

    11 hex is control CTRL-Q [using my brain to figure that out, so it may be wrong], so if you have XON/XOFF protocol, then XON is CTRL-Q, so that would be eaten by the low-level driver.

    Edit: The obvious solution is to disable XON/XOFF when setting up the COM-port. If you are sending binary data, you do not want XON/XOFF on the line - alternatively, you need to escape CTRL-Q, CTRL-S and by prefixing by some other unusual character and changing the CTRL-Q/S to something else [and like \ in C, you would need to use two escape to make one escape].

    Last edited by matsp; 08-19-2008 at 09:59 AM.
    Compilers can produce warnings - make the compiler programmers happy: Use them!
    Please don't PM me for help - and no, I don't do help over instant messengers.

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