USB port receiving unexpected characters

[neil]

Hi Mark,
  When I have the usb cable between the processor and PC, I get character 'N' that keeps being picked by fnTaskUSB(..) routine even when I dont have an application communicating with my board. Would this be coming from the USB CDC driver within the PC?  Obviously when I take the cable out the characters stop coming in.

Neil

[mark]

Hi Neil

If the PC is not sending anything to the virtual COM port that the CDC is on you shouldn't receive anything.

Do you have a USB snooper to see whether there is data being sent?

Regards

Mark

[neil]

Hi Mark,
 I downloaded a fre USB snooper. Here is the file I exported which shows transfers..
Neil

[mark]

Hi Neil

I am not sure that I understand the XML content but I see that there are a few transfers taking place. Are these expected?

Regards

Mark

[neil]

Hi Mark,
 No, when I started the snooper, only the cable was connected no application was running that was connected to the virtual port.

Regards
Neil

[mark]

Hi Neil

If you run the CDC demo (with USB/UART mode of operation) you would also see the same as the snooper on the UART output (assuming that it is really being sent).
This would of course not be expected.

The CDC virtual COM port will appear in the device manager when connected, as a specific COM port. If you open a terminal emulator on this CO port can it actually connect or dos it say that it is already in use? If you can connect does it then stop the other transfers taking place?

regards

Mark