C# serialPort: Application hangs if there is no recipient on Write() (virtual null modem)

Question

I am developing a PC WinForms application in C# that needs to connect to a microcontroller later. For now, for testing purposes, I have created a virtual null modem on my computer and linked it with a terminal program.

The virtual null modem I'm using is "com0com": http://sourceforge.net/projects/com0com/

Here is a screenshot of the COM port pair settings:

In my application I use the component serialPort. This is how the serialPort is set up:

public bool SerialPortSetup(String cp)
{
    String port = cp;
    int baud = 19200;
    Parity parity = Parity.None;
    int databit = 8;
    StopBits stopbit = StopBits.One;

    try
    {
        // Initialize serial port
        serialPort1 = new SerialPort(port, baud, parity, databit, stopbit);
        serialPort1.DataReceived += new SerialDataReceivedEventHandler(serialPortDataReceived);
        serialPort1.Open();
        return true;
    }
    catch (Exception e)
    {
        MessageBox.Show(e.Message);
        return false;
    }
}

Other properties of the serialPort:

The terminal program that I've connected to COM2 is set up with the same baudrate, parity, databit, stopbit, etc. When I have connected my own app to COM1, and the terminal to COM2, it all works just fine. Both writing and reading in both directions.

However, when I don't use the COM2 port (that is, the terminal program is not opened), my app hangs just the second I start to use serialPort1.Write(str), where str is just a random string. When running my app from Visual Studio, I can only close it by stopping the debugging. It's not like Windows marks it as "not responding". Btw, I always check for an opened serialPort before I write to it.

I need this problem to go away. Ideas?

Answer 1

I know that this question is a bit on the old side, but I came across it when looking for a solution to the same problem.

You need to change a couple of settings in com0com, which are described here http://www.magsys.co.uk/comcap/onlinehelp/null_modem_emulator_com0com.htm.

In brief, you need to enable buffer overrun for the receiving port, and baud rate emulation on the sending port. This is simple to do using the dialog in the OP image.