Arduino UNO

Arduino UNO is based on ATmega328P Microcontroller, an 8-bit AVR Architecture based MCU from ATMEL. Arduino UNO comes in two variants: one consists of a 28-pin DIP Microcontroller while the other consists of 32 lead Quad Flat Package Microcontroller.

Layout

The Type-B USB connector on the left short edge of the board, which is used for powering on the board as well as programming the Microcontroller. There is also a 2.1 mm DC jack to provide external power supply.

Technical Specifications

MCU	ATmega328P
Architecture	AVR
Operating Voltage	5V
Input Voltage	6V – 20V (limit) 7V – 12V (recommended)
Clock Speed	16 MHz
Flash Memory	32 KB (2 KB of this used by bootloader)
SRAM	2 KB
EEPROM	1 KB
Digital IO Pins	24 (of which 6 can produce PWM)
Analog Input Pins	6

Power

There are a couple of ways in which you can power the UNO board. The first and easy way is using the Type-B USB Connector. The next way is to provide an unregulated supply in the range of 6V to 20V to VIN pin of the UNO (Pin number 26).
You can also supply the unregulated supply through the 2.1mm DC Jack, in which case, you can access the supplied voltage through the VIN Pin.

Memory

Strictly speaking, this is specific to the MCU i.e., ATmega328P, used on the Arduino UNO Board. There are three different memories available in ATmega328P. They are:

• 32 KB of Flash Memory
• 2 KB of SRAM
• 1 KB of EEPROM
• 0.5 KB of the Flash Memory is used by the bootloader code.

Input and Output Pins

Of the 32 pins available on the UNO board, 22 pins are associated with input and output. In that 14 pins (D0 to D13) are true digital IO pins, which can be configured as per you application using pinMode(), digitalWrite() and digitalRead() functions.
All these Digital IO pins are capable of sourcing or sinking 20mA of current (maximum 40mA is allowed). An additional feature of the Digital IO pins is the availability of internal pull-up resistor (which is not connected by default).
The value of the internal pull-up resistor will be in the range of 20KΩ to 50KΩ.
There are also 6 Analog Input Pins (A0 to A5). All the analog input pins provide a 10-bit resolution ADC feature, which can be read using analogRead() function.
An important point about Analog Input pins is that they can be configured as Digital IO pins, if required.
Digital IO pins 3, 5, 6, 9, 10 and 11 are capable of producing 8-bit PWM Signals. You can use analogWrite() function for this.

Communication Interfaces

Arduino UNO supports three different types of communication interfaces. They are:

• Serial
• I2C
• SPI

Perhaps the most common communication interface in the Arduino universe is the Serial Communication. In fact, the Arduino boards (UNO or Nano or Mega) are programmed using the serial communication.
Digital IO pins 0 and 1 are used as Serial RX and TX pins to receive and transmit serial data. These pins are connected to the serial pins of the on-board USB to Serial Converter IC.
Analog Input Pins A4 and A5 have alternative functions. They can be configured as SDA (A4) and SCL (A5) to support I2C or I2C or Two Wire Interface (TWI) communication.
The final communication interface is the SPI. Digital IO Pins 10, 11 12 and 13 can be configured as SPI pins SS, MOSI, MISO and SCK respectively.

Additional features

There is an on-board LED connected to digital IO pin 13. Use this LED to perform Blinky operations. The reference voltage for the internal ADC is by default set to 5V. But using the AREF pin, you can manually set the upper limit of the ADC.
Using the IOREF pin, you can set the reference voltage for Microcontroller operations.
To reset the microcontroller, you can use the on-board RESET button.
Although you can program the Arduino UNO using the USB cable, there is a provision to program the MCU using the In-Circuit Serial Programming (ICSP) interface.
The UART bootloader, which is preloaded in to the ATmega328P microcontroller, enables programming through serial interface. But ICSP doesn’t need any bootloader.
You can program Arduino UNO using ISCP or use the ISCP of Arduino UNO to program other Arduino Boards.
Digital IO Pins 2 and 3 can be configured as External Interrupts Pins INT0 and INT1 respectively. Use attachInterrupt() function to configure the Interrupt for rising edge, falling edge or level change on the pin.

Pinout

Pin Description

For pin description of Arduino UNO, let us assume some basic numbering. Let the numbering begin with the RX Pin (D0). So, RX is Pin 1, TX is Pin 2, D2 is Pin 3 and so on.
On the other side, NC is Pin 19, IOREF is Pin 20 etc. Overall, there are 32 pins on the Arduino UNO Board.

Pin Number	Pin Name	Description	Alternative Functions
1	RX/D0	Digital IO Pin 0 Serial RX Pin	Generally used as RX
2	TX/D1	Digital IO Pin 1 Serial TX Pin	Generally used as TX
3	D2	Digital IO Pin 2
4	D3	Digital IO Pin 3	Timer (OC2B)
5	D4	Digital IO Pin 4	Timer (T0/XCK)
6	D5	Digital IO Pin 5	Timer (OC0B/T1)
7	D6	Digital IO Pin 6
8	D7	Digital IO Pin 7
9	D8	Digital IO Pin 8	Timer (CLK0/ICP1)
10	D9	Digital IO Pin 9	Timer (OC1A)
11	D10	Digital IO Pin 10	Timer (OC1B)
12	D11	Digital IO Pin 11	SPI (MOSI) Timer (OC2A)
13	D12	Digital IO Pin 12	SPI (MISO)
14	D13	Digital IO Pin 13	SPI (SCK)
15	GND	Ground
16	AREF	Analog Reference
17	SDA/D18	Digital IO Pin 18	I2C Data Pin
18	SCL/D19	Digital IO Pin 19	I2C Clock Pin
19	NC	Not Connected
20	IOREF	Voltage Reference
21	RESET	Reset (Active LOW)
22	3V3	Power
23	5V	+5V Output from regulator or +5V regulated Input
24	GND	Ground
25	GND	Ground
26	VIN	Unregulated Supply
27	A0	Analog Input 0	Digital IO Pin 14
28	A1	Analog Input 1	Digital IO Pin 15
29	A2	Analog Input 2	Digital IO Pin 16
30	A3	Analog Input 3	Digital IO Pin 17
31	A4	Analog Input 4	Digital IO Pin 18	I2C (SDA)
32	A5	Analog Input 5	Digital IO Pin 19	I2C (SCL)

Pins of the ICSP Connector

MISO	Master In Slave Out (Input or Output)
5V	Supply
SCK	Clock (from Master to Slave)
MOSI	Master Out Slave In (Input or Output)
RESET	Reset (Active LOW)
GND	Ground

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