This Rev3 version of the Arduino UNO is a microcontroller board based on the ATmega328P. It has 14 digital input/output pins (of which six can be used as PWM outputs), six analog inputs, a 16 MHz ceramic resonator (CSTCE16M0V53-R0), a USB connection, a power jack, an ICSP header, and a reset button. It contains everything needed to support the microcontroller; simply connect it to a computer with a USB cable or power it with an AC-to-DC adapter or battery to get started.
The Arduino UNO can be programmed with the Arduino Software (IDE). It comes preprogrammed with a bootloader that allows you to upload new code to it without the use of an external hardware programmer. It communicates using the original STK500 protocol. The ATmega328 has 32 KB (with 0.5 KB occupied by the bootloader). It also has 2 KB of SRAM and 1 KB of EEPROM.
The board can operate on an external supply from 6 to 20 V. If supplied with less than 7 V, however, the 5 V pin may supply less than five volts and the board may become unstable. If using more than 12 V, the voltage regulator may overheat and damage the board. The recommended range is 7 to 12 V.
This UNO differs from all preceding boards in that it does not use the FTDI USB-to-serial driver chip. Instead, it features the ATmega16U2 (ATmega8U2 up to version R2) programmed as a USB-to-serial converter. It also has a stronger RESET circuit.