Re: Serial port communication - C# Discussion Boards

4-Mar-08 3:59

Hello everybody
My project is a C# project on VS2005.
My application communicate with external device through Serial Port.I'm using USB to RS convertor whitch add another COM Port in my computer.When I connect with device through this COM Port(transmit and receive data) everythink is OK.When unplug the USB cable from PC and I try to transmit data the program is generate exeption.How can I detect when the COM Port is disappear?
Thanks in advance

Matthew Butler4-Mar-08 4:46

Matthew Butler

4-Mar-08 4:46

Hi,

I beleive you are looking for .IsOpen

I've just tried this with a USB-Serial converter and it works. (Goes false on a disconnect).

It doesn't cause an event though.

Matthew Butler

t_nedelchev4-Mar-08 20:45

4-Mar-08 20:45

Sorry but it doesn't works.
My code is

if (sp.IsOpen)
{
sp.Write(TxBuf, 0, (k + 2 + ofs));
}
else
{
FL_Connected = false;
MessageBox.Show("Message");
}
When I unplug USB cable (Converter) from my computer the COM Port is still yet open but when the program try to write data to serial port it's generate exception "Access to the Port is denied"

DaveyM694-Mar-08 22:19

4-Mar-08 22:19

You should always put communication like this in a try/catch block so you can catch exceptions like this.

It may be worth starting a timer when you open your port, pausing it when you're about to read/write and stopping it when you close it. That way you can test the port on each Tick event so you always know when it's connected/disconnected.

You can also monitor USB devices, get notified when one is inserted/removed and check if it's the one you're intersted in so you can act accordingly. There are some articles on this site if you search.

Dave

t_nedelchev4-Mar-08 22:59

4-Mar-08 22:59

thanks for an answer
I try to do this
try
{
sp.Write(TxBuf, 0, (k + 2 + ofs));
}
catch
{
FL_Connected = false;
MessageBox.Show("Message");
}
And it works.But when I close the program it generate the same exception(Access to the port is denied)

DaveyM694-Mar-08 23:53

4-Mar-08 23:53

Are you closing the port when you're finished with it? It sounds like you're keeping it open and the program is trying to close the port when it ends - which will generate an exception if it's not available. If you need to keep the port open for the duration, you should close the port manually in the formclosing event - and again, put that inside a try/catch block.

Dave

t_nedelchev5-Mar-08 0:05

5-Mar-08 0:05

Thanks DaveyM69
I try to do this

protected override void OnClosing(CancelEventArgs e)
{
try
{
sp.Close();
}
catch
{
int probe = 33;
}
}
In this case there is no exception when close the program but the program is stoped on the breakpoint in the catch.
There is something interesting.When I start the program again the all window is white for a 2 or 3 seconds and then starts normaly.

DaveyM695-Mar-08 0:51

5-Mar-08 0:51

Hmm... Looks like it's taking a while for it to Dispose. You could try calling Dispose() or Dispose(true) and maybe even do a GC.Collect() to force the clean up.

First thing I'd do is see what exceptions if any are occurring

catch(System.Exception ex)
{
   System.Windows.Forms.MessageBox.Show(ex.InnerException.Message);
}

Dave

t_nedelchev5-Mar-08 1:16

5-Mar-08 1:16

The problem is when I unplug the USB converter from PC and COM Port is disapear any tring of using a method of instance of serial port generate exception i.e. I can't use Sp.Dispose() or SP.Close();

DaveyM695-Mar-08 1:25

5-Mar-08 1:25

Maybe check if it's null before doing any operations?

public static bool IsPortAvailable(System.IO.Ports.SerialPort portToTest)
{
   return !(null == portToTest);
}

Dave

t_nedelchev5-Mar-08 1:40