... copy, not the additionalI2C interface), plus the two next to the RESET pin, one IOREF allow expansion board voltage onboard, this pinexpansion ... changed, has been moved to the corner near the USB interface board, more convenient and press.The 3. ATmega16U2 instead 8U2, and ... run faster, this update is a service of the USB interface chip, theoretically It UNO can simulate USB the HID, such ...