- A product for Arduino that works with official Arduino boards;
- More pins: 2 more I2C pins are added by the side of AREF pin (SDA and SCL, copies of Analog 4 and 5, not extra I2C interfaces); Moreover, 2 more other pins are also added by the side of RESET, one is IOREF, which enables the expansion board to adapt to the on-board voltage (just tell you the current on-board voltage), and the other one is a stand-by occupied pin;
- More stable RESET circuit: The RESET has been moved to the board corner, near to the USB interface, which is more convenient to use;
- ATmega16U2 replaces 8U2, but this doesn't mean that the R3 with 16K flash can make your code run faster, it is just updated to serve for the USB interface chip. In theory, this update allows UNO to simulate USB HID, such as MIDI / Joystick / Keyboard.