public MyForm()
{
    InitializeComponents();  // Initialize Form Components
    com.RThreshold = 1;  // Fire OnComm event after any data is received
    com.OnComm += new System.EventHandler(this.OnComm);  // Assigns the event handler
}

private void OnComm(object sender, EventArgs e)  //  MSCommLib OnComm Event Handler
{
    if (com.InBufferCount > 0) ProcessData((string) com.Input);
    if (com.CommEvent == MSCommLib.OnCommConstants.comEvCTS)
        Console.WriteLine("CTS Line Changed");
}

           DB9 Female to DB9 Female

       2 |  3 |  7 |  8 | 6&1|  5 |  4
     ---- ---- ---- ---- ---- ---- ---- 
       3 |  2 |  8 |  7 |  4 |  5 | 6&1



          DB25 Female to DB25 Female

        2 |  3 |  4 |  5 | 6&8|  7 | 20 
      ---- ---- ---- ---- ---- ---- ----
        3 |  2 |  5 |  4 | 20 |  7 | 6&8

          DB9 Male (Pin Side)                   DB9 Female (Pin Side)
          DB9 Female (Solder Side)              DB9 Male (Solder Side)
              -------------                          -------------
              \ 1 2 3 4 5 /                          \ 5 4 3 2 1 /
               \ 6 7 8 9 /                            \ 9 8 7 6 /
                ---------                              ---------


   DB25 Male (Pin Side)                    DB25 Female (Pin Side)
   DB25 Female (Solder Side)               DB25 Male (Solder Side)
    ---------------------------------       ---------------------------------
    \ 1  2  3  4  5  6  7  8 ... 13 /       \ 13 ... 8  7  6  5  4  3  2  1 /
     \ 14 15 16 17 18 19 20 ... 25 /         \ 25 ... 20 19 18 17 16 15 14 /
      -----------------------------           -----------------------------

// Constructor for Form with an AxMSCommLib control on it named "com"
public SerialTerm()
{
    // Initialize Form Components
    InitializeComponent();

    // Initialize the COM Port control
    InitComPort();

    // Send data out through the COM port
    com.Output = "Serial Terminal Initialized";
}

private void InitComPort()
{
    // Set the com port to be 1
    com.CommPort = 1;
    
    // This port is already open, close it to reset it.
    if (com.PortOpen) com.PortOpen = false;
    
    // Trigger the OnComm event whenever data is received
    com.RThreshold = 1;  
    
    // Set the port to 9600 baud, no parity bit, 8 data bits, 1 stop bit (all standard)
    com.Settings = "9600,n,8,1";

    // Force the DTR line high, used sometimes to hang up modems
    com.DTREnable = true;
    
    // No handshaking is used
    com.Handshaking = MSCommLib.HandshakeConstants.comNone;

    // Don't mess with byte arrays, only works with simple data (characters A-Z and numbers)
    com.InputMode = MSCommLib.InputModeConstants.comInputModeText;
    
    // Use this line instead for byte array input, best for most communications
    //com.InputMode = MSCommLib.InputModeConstants.comInputModeText;
    
    // Read the entire waiting data when com.Input is used
    com.InputLen = 0;

    // Don't discard nulls, 0x00 is a useful byte
    com.NullDiscard = false;
    
    // Attach the event handler
    com.OnComm += new System.EventHandler(this.OnComm);
    
    // Open the com port
    com.PortOpen = true;  
}

private void OnComm(object sender, EventArgs e)  //  MSCommLib OnComm Event Handler
{
    // If data is waiting in the buffer, process it.
    // Note: This is using the string method for simple data, be sure
    //       to use byte arrays (described below) for more generic data.
    if (com.InBufferCount > 0) ProcessComData((string) com.Input);
}

private void ProcessComData(string input)
{
    // Send incoming data to a Rich Text Box
    rtfTerminal.AppendText(input + "\n");
}

public short FindDevicePort()
{
    bool PortOkay = true; short TestPort = 0;
    bool found = false;  // Init variables for checking.

    // Stop the OnComm event and normal processing.
    com.RThreshold = 0;
    
    // Close the current port if one is already open.
    if (com.PortOpen) com.PortOpen = false;

    do
    {
        TestPort++;  // Try the next port
        PortOkay = true;
        
        // Attempt to access this port number (mayby it doesn't exist on this computer)
        try {com.CommPort = TestPort;}
        catch (System.Runtime.InteropServices.COMException)
        {PortOkay = false;}
        
        if (PortOkay)  // Continue if the port exists
        {
            // Attempt to open the port (maybe it's already in use by another program)
            try {com.PortOpen = true;}
            catch (System.Runtime.InteropServices.COMException)
            {PortOkay = false;}

            if (PortOkay) // Continue if port was available and opened
            {
                com.Output = "Hello?";  // Send string to request a response.

                long TimeStamp = DateTime.Now.Ticks;  // Time Stamp for Time-out
                string buffer = "";
                bool ElapsedTime;
                do
                {
                    // Don't lock up the entire application,
                    // release control to process other messages.
                    System.Windows.Forms.Application.DoEvents();
                    
                    // If there is data waiting, buffer it in our own string buffer.
                    if (com.InBufferCount > 0) buffer += com.Input;

                    // Look for response from device.
                    found = (buffer.IndexOf("Hi There") > -1);  

                    // True if time is up, change the 0.2 for human interaction
                    ElapsedTime = DateTime.Now.Ticks - TimeStamp >
                                  TimeSpan.TicksPerSecond * 0.2;

                // Keep waiting until found or 0.2 seconds are up.
              } while (!ElapsedTime & !found);
            }
        }
    } while ((TestPort < 4) & !found);

    // If the device was found, return the port it was found on
    if (found) return TestPort;
    
    // Device not found, return 0.
    return 0;
}