The UNO R3 Red board is based on the ATmega328P microcontroller. It features 14 digital input/output pins (6 of which 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. It contains everything you need to support the microcontroller. Simply connect it to a computer with a USB cable or power it with an AC-DC adapter or battery to get started.

Differences from other boards:

The UNO R3 board differs from all previous ones as it does not use the FTDI USB-to-serial chip. Instead, it features the Atmega16U2 (Atmega8U2 up to version R2) programmed as a USB-to-serial converter.

Revisions:

The revision 3 of the board has the following new features:

• 1.0 pinout design: added SDA and SCL pins near the AREF pin and two other new pins placed near the RESET pin, the IOREF that allows shields to adapt to the voltage provided by the board.
• Capability of compatibility with the board using the AVR, operating on 5V, and with the Arduino Due operating on 3.3V.
• Increased RESET circuit durability.

Technical Specifications:

• Model: UNO R3 (Revision 3)
• Microcontroller: ATmega328
• CH340 for USB/Serial interface
• Operating Voltage: 5V
• Input Voltage (recommended): 7-12V
• Input Voltage Limits: 6-20V
• Digital Pins: 14 (of which 6 provide PWM output)
• Analog Inputs: 6
• DC Current per I/O Pin: 40 mA
• DC Current for 3.3V Pin: 50 mA
• Flash Memory: 32 KB (ATmega328) of which 0.5 KB is used by the bootloader
• SRAM: 2 KB (ATmega328)
• EEPROM: 1 KB (ATmega328)
• Clock Speed: 16MHz
• Length: 68.6 mm
• Width: 53.4 mm
• Weight: 25 g
• Built-in bootloader.
• Female header: Mounted female header.
• The memory of the ATmega328 is 32 KB (with 0.5 KB occupied by the bootloader). It also has 2 KB SRAM and 1 KB EEPROM.