History Arduino RS232 Serial board - a predecessor with an ATmega8 Instead, it uses the Atmega16U2 (Atmega8U2 up to version R2) programmed as a USB-to-serial converter. While the Uno communicates using the original STK500 protocol, it differs from all preceding boards in that it does not use a FTDI USB-to-UART serial chip. The ATmega328 on the board comes preprogrammed with a bootloader that allows uploading new code to it without the use of an external hardware programmer. Version 1.0 of the Arduino IDE for the Arduino Uno board has now evolved to newer releases. The Uno board was the successor of the Duemilanove release and was the 9th version in a series of USB-based Arduino boards. The word ' uno' means 'one' in Italian and was chosen to mark a major redesign of the Arduino hardware and software. Layout and production files for some versions of the hardware are also available. The hardware reference design is distributed under a Creative Commons Attribution Share-Alike 2.5 license and is available on the Arduino website. It has the same microcontroller as the Arduino Nano board, and the same headers as the Leonardo board. It can be powered by a USB cable or a barrel connector that accepts voltages between 7 and 20 volts, such as a rectangular 9-volt battery. The board has 14 digital I/O pins (six capable of PWM output), 6 analog I/O pins, and is programmable with the Arduino IDE (Integrated Development Environment), via a type B USB cable. The microcontroller board is equipped with sets of digital and analog input/output (I/O) pins that may be interfaced to various expansion boards (shields) and other circuits. The Arduino Uno is an open-source microcontroller board based on the Microchip ATmega328P microcontroller (MCU) and developed by and initially released in 2010.

Arduino board uno datasheet