Arduino Due Core and USARTClass.h

Official Hardware Mega Due
2

Hello Mainian,

The USARTClass files (.h,.cpp) are part of the Arduino IDE 1.5.X. You can find them in the following path:

...\arduino-1.5.X-windows\arduino-1.5.X\hardware\arduino\sam\cores\arduino

Here also a link related to your topic:

http://forum.arduino.cc/index.php?topic=162959.0

I hope that can be of help.
-P