Is there a timeout or waiting time for Serial Ports?

Question

I'm working with a measurement system that is connected to my computer trough a com cable.
Everything is fine but in a different time intervall under the same conditions the device stops sending codes...
I dunno why but may you can help me.
Here's my connection

 // Set the port's settings
                    comport.BaudRate = 9600;
                    comport.DataBits = 7;
                    comport.Parity = Parity.Even;
                    comport.Handshake = Handshake.XOnXOff;
                    comport.RtsEnable = true;
                    comport.ReadTimeout = 500;
                    comport.WriteTimeout = 500;
                    comport.PortName = portname;

Is there maybe a timeout or a datalimit or so?
So it stops sending ?

Edit: I'm sending codes like 10 with a 1 second waiting time between every. Maybe to short?