Windows enumerate USB devices -- list usb: USBView

• https://msdn.microsoft.com/en-us/library/windows/hardware/ff560019(v=vs.85).aspx 
• https://dev.windows.com/en-us/downloads/sdk-archive 
• and install only the "debugging tools for Windows".

Install path is
C:\Program Files (x86)\Windows Kits\8.1\Debuggers\x86\usbview.exe

There's also an x64 one but it's still under Program Files x86:
C:\Program Files (x86)\Windows Kits\8.1\Debuggers\x64\usbview.exe

Note on DigiX:
https://digistump.com/wiki/digix/tutorials/programming
Bootloader is SAM-BA with VID/PID 03EB/6124
Native USB mode is VID/PID 2341/003E

However DigiX appears with VID 0x16D0 and PID 0x078A

From http://digistump.com/board/index.php?topic=1185.20
VID : PID
03EB:6124   Atmel: SAM-BA activated device
2341:003E   Arduino DUE native PORT selected, sketch is running
16d0:078a   DigiX board selected, sketch is running

Now open Device Manager > Ports (COM & LPT).

It shows "Digistump DigiX (COM6)".

But since the Arduino IDE expects COM3, change it: device manager > Ports > DigiX (COM6) > Properties > Port Settings > Advanced > … won't do COM3 says "in use" (by whom).

Nevermind, change IDE to match COM6: Arduino 1.6.5 > Tools > Port > COM6.

Note by default the Arduino IDE expects 9600 bauds so make sure the sketch inits with this as early as possible:  Serial.begin(9600);