in reply to Re^3: Win32:SerialPort not reading all characters
in thread Win32:SerialPort not reading all characters

BrowserUK, You idea solved the problem. I was able to check the status of the com port before and after running different programs and using the copy to port mechanism.

What I found was that I was using xoff for handshaking and when I changed that to none the additional characters come through Win32::SerialPort. Looks like xoff handshaking handles certain bytes differently.

Thanks for the guidance.

Mike

  • Comment on Re^4: Win32:SerialPort not reading all characters

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Re^5: Win32:SerialPort not reading all characters
by BrowserUk (Patriarch) on Mar 31, 2008 at 22:03 UTC

    That makes a certain amount of sense. Traditionally software handshaking was only used for keyboard/terminal devices where on 'printable' character code were data and the control characters are reserved for control purposes. xon/xoff being done with ^Q/^S and the other control characters had defined meanings: 

    SOH (Start of Heading)
STX (Start of Text)
ETX (End of Text)
EOT (End of Transmission
ENQ (Enquire)
ACK (Acknowledge)
BEL (Bell)
BS  (Backspace)
HT  (Horizontal Tab)
VT  (Vertical Tab)
FF  (Form Feed)
SO  (Shift Out)
SI  (Shift In)
DLE (Data Link Escape)
DC1 (Device Control 1/X-On)
DC2 (Device Control 2)
DC3 (Device Control 3/X-off)
DC4 (Device Control 4)
NAK (Negative Acknowledgement)
SYN (Synchronous Idle)
ETB (End of Transmission Block)
CAN (Cancel)
EM  (End of Medium)
SUB (Substitute)
ESC (Escape)
FS  (File Separator)
GS  (Group Separator)
RS  (Record Separator)
US  (Unit Separator)

    [download]
    It's quite possible that the serial device driver retains special handling for some of those characters when xon is enabled.

    With modern UARTs and FIFO buffering, handshaking is often unnecessary, at least at resonably low speeds, but if your device supports one of the flavours of hardware handshaking, it would be a good idea to enable that.

    Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
    "Science is about questioning the status quo. Questioning authority".
    In the absence of evidence, opinion is indistinguishable from prejudice.
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