C / C++ / MFC

DWORD                   dwNumBytesRead;
DWORD                   dwNumBytesWritten;
SECURITY_ATTRIBUTES     sa;

sa.nLength = sizeof(SECURITY_ATTRIBUTES);
sa.lpSecurityDescriptor = NULL;     // use default descriptor
sa.bInheritHandle = true;               // allow sub-threads to inherit handle

// OPEN SERIAL PORT FOR COMMUNICATION
m_hSerialPortHandle = CreateFile((LPCTSTR)m_csCommPortName,
    GENERIC_READ | GENERIC_WRITE,
    0,
    &sa,                            // needed for inherit
    OPEN_EXISTING,
    0,
    0);

if (m_hSerialPortHandle != INVALID_HANDLE_VALUE)
{
    m_bOpen = true;

    if (!GetCommState(m_hSerialPortHandle, &m_DCB))
    {
        text = "Serial port DCB failure.";
        ::SendMessage(m_hwndParent, UWM_UC_STATUS, (LONG)(LPCTSTR)text, 0);
    }
    else
    {
        // make sure we are using the correct settings
        m_DCB.BaudRate = CBR_9600;                  // 9600 baud
        m_DCB.ByteSize = 8;                     // 8 data bits
        m_DCB.Parity = NOPARITY;                    // no parity
        m_DCB.fParity = false;                      // parity checking off
        m_DCB.StopBits = ONESTOPBIT;                // 1 stop bit
        m_DCB.fDtrControl = DTR_CONTROL_DISABLE;    // no DTR input flow control
        m_DCB.fOutxCtsFlow = false;             // don't monitor CTS
        m_DCB.fDsrSensitivity = false;              // always read bytes received
        m_DCB.fTXContinueOnXoff = true;         // don't wait for XONN / XOFF
        m_DCB.fOutX = false;                        // No XON / XOFF control
        m_DCB.fRtsControl = RTS_CONTROL_DISABLE;    // don't use RTS comms control
        m_DCB.fAbortOnError = false;                // don't quit on error

        // now apply the correct comm state to the device
        if (!SetCommState(m_hSerialPortHandle, &m_DCB))
        {
            text = "Serial port set com status failure.";
            ::SendMessage(m_hwndParent, UWM_UC_STATUS, (LONG)(LPCTSTR)text, 0);
        }
        // set the communication event flags
        if (!SetCommMask(m_hSerialPortHandle, EV_RXCHAR))
        {
            text = "Serial port set com mask failure.";
            ::SendMessage(m_hwndParent, UWM_UC_STATUS, (LONG)(LPCTSTR)text, 0);
        }
        COMMTIMEOUTS    timeouts;

        // return immediately on reads
        // return after completion on writes
        timeouts.ReadIntervalTimeout = MAXDWORD;
        timeouts.ReadTotalTimeoutConstant = 0;
        timeouts.ReadTotalTimeoutMultiplier = 0;
        timeouts.WriteTotalTimeoutConstant = 0;
        timeouts.WriteTotalTimeoutMultiplier = 0;

        SetCommTimeouts(m_hSerialPortHandle, &timeouts);
    }
}
else
{
    text = "Unable to open serial port \"" + m_csCommPortName + "\"";
    ::SendMessage(m_hwndParent, UWM_UC_STATUS, (LONG)(LPCTSTR)text, 0);
    m_bThreadDead = true;
    return;
}

// COMM PORT OPEN Now talk to connected instrument
while (!m_bKillThread)
{
    // we loop until m_bKillThread becomes true

    // calls to WriteFile()...

    // Read stuff (1 byte at a time)
    ReadFile(m_hSerialPortHandle, szInputBuffer, 1, &dwNumBytesRead, NULL);
    //TRACE("%c 0x%x\n", szInputBuffer[0], (int)szInputBuffer[0]);
    if (dwNumBytesRead == 1)
    {
    // do something withthe read data
    }
}
// release resources
CloseHandle(m_hSerialPortHandle);
m_bOpen = false;
m_bThreadDead = true;
m_bKillThread = false;
// thread dies on exit of routine