Pin change:

Two I2C pins are added on the side of pin AREF (SDA and SCL, just the copy of Analog 4and 5, not an additional I2C interface). In addition, add 2 pins alongside the RESET, one is IOREF, which can make the expansion board adapt to board voltage. This pin is to tell expansion board the present onboard voltage (for example, when UNO is 5V, which can be seen as a copy of the power supply pin, does not provide a level pull-up) ;the other is an occupy pin to be used later.

More stable RESET circuit. The position of RESET key was also changed, moved to board corner near the USB interface, which is more convenient to press.

8U2 was replaced by ATmega16U2. This does not mean that there is R3 with 16K flash let your code run fast, this update is for USB interface chip. In theory, it let UNO can simulate USB HID such as MIDI/Joystick/Keyboard.

Specification:

Operating Voltage:5V

Input Voltage(recommended):7-12V

Input Voltage(limits):6-20V

Digital I/O Pins:14(of which 6 provide PWM output)

Analog Input Pins:6

DC Current per I/0 Pin:40mA

DC Current for 3.3V Pin: 50mA

Flash Memory: 32KB(ATmega328)of which 0.5KB used by bootloader

SRAM:2KB (ATmega328)

EEPROM:1KB(ATmega328)

Clock Speed:16MHz

Package Includes: 

Funduino UNO R3 Development Board x1