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[Return]                  Opening a Serial Port                   [Return]

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          Windows used to have a set of communication (serial) functions
  which, although not the greatest thing in the world, was a distinct
  set of functions for that purpose. Win32 made things considerably
  easier in most aspects, but the functionality was absorbed by generic
  file functions which, I am assuming, is at least part of the reason
  why I've heard so many questions concerning COM functions and Win32
  systems.

          Below is a routine used to open a communication port passed to
  the function as an integer value. First, the port is opened and
  timeout values are set to "no timeout", meaning ReadFile() will return
  immediately whether something is waiting to be read or not. Next, the
  port is set to 9600 baud, no parity, 8 data bits and one stop bit. The
  open port handle is then returned to the caller assuming there were no
  errors, in which case INVALID_HANDLE_VALUE is returned.

          Once the port is open, ReadFile(), WriteFile() and other like
  functions may be used to send and receive data on the port.
  CloseHandle() is called to close the port.

 HANDLE OpenCOMPort( int iPort )
 {
    char szStr[ 64 ];
    COMMTIMEOUTS cto;
    HANDLE hPort;
    DCB dcb;

    wsprintf( szStr, "COM%d", iPort );                  //  Specify port to open
    hPort = CreateFile( szStr, GENERIC_READ | GENERIC_WRITE, 0, NULL,
                        OPEN_EXISTING, 0, NULL );

    if( hPort == INVALID_HANDLE_VALUE )             //  Open port or do bad exit
       return( INVALID_HANDLE_VALUE );

    memset( &cto, 0, sizeof(COMMTIMEOUTS) );              //  Set timeout values
    cto.ReadIntervalTimeout = MAXDWORD;                        //  to no timeout
    SetCommTimeouts( hPort, &cto );               //  so ReadFile() doesn't hang

    memset( &dcb, 0, sizeof(DCB) );                  //  Initialize the port DCB
    wsprintf( szStr, "COM%d: baud=9600 parity=N data=8 stop=1", iPort );

    dcb.DCBlength = sizeof(DCB);                      //  Specify structure size
    if( ! BuildCommDCB( szStr, &dcb ) )                  //  If DCB fails...quit
    {
       CloseHandle( hPort );
       return( INVALID_HANDLE_VALUE );
    }

    if( ! SetCommState( hPort, &dcb ) )                    //  Apply DCB to port
    {                                                     //  or quit on failure
       CloseHandle( hPort );
       return( INVALID_HANDLE_VALUE );
    }

    return( hPort );
 }