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

Question

I am trying to connect to a virtual com port provided by the drivers of a u-blox GPS device.

The device appears normally under the Sensors tab in Device Manager and I can really get the coordinate data using GeoCoordinateWatcher class from C#.

But I want to read the underlying NMEA data. So in the process of doing that I installed the Virtual Com Port driver provided by U-BLOX and it generated a u-blox virta com port in devices manager.

Connecting to that using Putty is OK and I can see all the NMEA lines being dumped there.

but when I try to connect to the same port (after Putty is closed obviously) using C# I get the exception mentioned in the title

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

My code is fairly simple (not the first time I use com ports) and everything is correctly defined (Port Name, Stop Bits, Parity, BaudRate etc). I even tried changing to a "wrong" com port name to see the exception I will get and it is completely different (Com Port does not a exit exception).

So what is happening with C# at this point? Am I doing something wrong? Is this a bug in the SerialPort class? Putty seems to work just fine in connecting and streaming the data. My code is as simple as the following

m_port = new SerialPort
{
    PortName = m_portName,
    BaudRate = m_baudRate,
    Parity = m_parityBit,
    DataBits = m_dataBits,
    StopBits = m_stopBit
};

m_port.Open();

I even tried hardcoding the values and I still get the same exception. I tried many of the suggested solutions found here, none of them helped. I also tried changing the COM port number from Device Manager advanced settings, that also did not help

Have you tried renaming the COM port and use the new name instead of old one. — JSR
I haven't worked with u-blox.. but I hope the below be useful for you.. forum.u-blox.com/index.php/9380/… . It seems there are some issues with connecting to serial port as it won't behave like the exact serial port. — JSR
We use an Ethernet modual called NetBurner. They have a really nice application for setting up true virtual COM ports. Maybe give that a try, I have no issues connecting to the VCOMs I made with my C# app. netburner.com/support/documents/sb70/deployment-tools-9/… — Baddack

John Demetriou John Demetriou · Accepted Answer · 2018-11-01T15:49:14

As it turns out U-BLOX virtual COM port driver does not fully emulate a COM port which causes issues with .Net. Regardless if it is C# or C++ or any other language running on .Net The only solution is to either, not use this device, or use an intermediary software.

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

3 Answers