design of the Arduino board, the ELECTRONOOBINO V1.0. You ahev the step by step tutorial below on how to get the bare minimum configuration for this chip.

The UNO is a microcontroller board based on the ATmega328. It has 14 digital input/output pins (of which 6 can be used as PWM outputs), 6 analog inputs, a 16 MHz crystal oscillator, a USB connection, a power jack, an ICSP header, and a reset button.

Using The Second Microcontroller On An Arduino
http://hackaday.com/2014/11/30/using-the-second-microcontroller-on-an-arduino/

While newer Arduinos and Arduino compatibles either have a chip capable of USB or rely on a V-USB implementation, the old fogies of the Arduino world, the Uno and Mega, actually have two chips. An ATMega16u2 takes care of the USB connection, while the standard ‘328 or ‘2560 takes care of all ~duino tasks. Wouldn’t it be great is you could also use the ’16u2 on the Uno or Mega for some additional functionality to your Arduino sketch? That’s now a reality. [Nico] has been working on the HoodLoader2 for a while now, and the current version give you the option of reprogramming the ’16u2 with custom sketches, and use seven I/O pins on this previously overlooked chip.

Setup is simple enough, only requiring a connection between the ‘328 ISP header and the pins on the ’16u2 header

USB functions with Arduino Leonardo/Micro/Uno/Mega and HID Project
http://nicohood.wordpress.com/2014/06/12/usb-functions-with-arduino-leonardomicrounomega-and-hid-project/

If you’re looking to make your own shield for the Arduino platform, you’ll definitely need to know where all the pins and holes are located on the Arduino.

a detailed technical drawing of both the Uno and Mega 2560. The drawings are available in vector-based SVG format, but low-resolution PNG files are shown