Unable to open serial port in .NET

Question

I am trying to open COM1, but get a strange error every time I call SerialPort.Open().

The error is:

The given port name does not start with COM/com or does not resolve to a valid serial port. Parameter name: portName

The code is very simple:

SerialPort port = new SerialPort("COM1", 19200, Parity.None, 8, StopBits.One);
port.Handshake = Handshake.RequestToSend;
port.Open();

If I call SerialPort.GetPortNames(), it returns one port called "COM1".

I've verified that I have a "COM1" on my computer, and I'm not using it in any other applications. When I run the code on another computer, it works. My system is running Windows Vista. The version of .NET is 2.0.

Is there a security setting I have to change somewhere? I'm logged in as an admin, and have UAC turned off.

---

More info

I used Process Explorer and confirmed that nothing is using \Device\Serial0.

---

Workaround

I installed a USB-Serial adaptor (COM3), and it works fine. Go figure. There must be a problem with COM1.

Answer 1

Maybe a typo? Ensure that you are typing COM1 in all english letters.

Answer 2

Try to use the notation \.\COMX instead of just COMX. Ensure you escape the characters: "\\.\COM1"

Edit:Wops, SO escapes my \ so it should be like this (ommit spaces): "\ \ \ \ . \ \ COM1"

Answer 3

You could try setting up the properties of the port, rather than using the constructor.

mPort = new System.IO.Ports.SerialPort();
if(mPort.IsOpen)
{
   mPort.Close();
}
mPort.PortName = "COM1";
mPort.BaudRate = 19200;
mPort.Parity = Parity.None;
mPort.DataBits = 8;
mPort.StopBits = StopBits.One;
mPort.Handshake = Handshake.RequestToSend; // Handshake.None;
mPort.Open();

I've also run into problems with Serial comm's and Microsoft Active Sync. I'm not sure if you have this running or not, but it might be worth a shot to kill it (process name in the Task Manager is wcescomm.exe). Hope that helps.

You could also try and use Marshal.GetLastWin32Error() to see if something low level is causing a problem? I'm not sure if that will give you more information.