Arduino Uno

Arduino Uno is the latest version of the Arduino boards (next to the Duemilanove). The major difference from the previous board is in that it uses the Atmega8U2 micro-controller (instead of FTDI) for communicating with a computer. The Atmega8U2 is programmed as a USB to serial converter by default, but it can be programmed as any other USB devices (keyboard, mouse, joystick and etc...).

Arduino Uno

To upload a new firmware to the Atmega8U2, we need to reset the chip and put it into a DFU mode. There is a description in the Ardunio site how to do that. It can be done easily using 2 M/M jumper wires

M/M jumper wire

Instead of using ground pads(from the description in Arduino site), we can use Arduino's GND pins.
1)Connect Arduino Uno to the computer
2)Hold first wire as pictured in the below image.
3)Connect second wire.
4)Remove second wire then remove first.

Now your Arduino is in DFU mode

The Device manager (in windows 7)

To return to the USB to serial converter mode, just disconnect and connect Arduino.
The upload of a firmware will be in the next article.