I²C (Inter-Integrated Circuit), pronounced I-squared-C, is a synchronous, multi-master, multi-slave, packet switched, single-ended, serial communication bus invented in 1982 by Philips Semiconductor (now NXP Semiconductors). It is widely used for attaching lower-speed peripheral ICs to processors and microcontrollers in short-distance, intra-board communication. Alternatively, I²C is spelled I2C (pronounced I-two-C) or IIC (pronounced I-I-C).

Hardware

• SDA : The Data line (Serial Data Line).
• SCL: The Clock line (Serial Clock Line).
• Rp : pull-up resistors.
• VD: 3.3v to 5V (for Arduino Uno 5V)
• Master : The architecture can accept more than one master.
• Slaves : 112 max slaves.
• Wires : no longer than 2 m.

I2C: Master as sender configuration

• Code of the Master :

// Wire Master Writer
#include <Wire.h>

void setup()
{
  Wire.begin();               // join i2c bus (address optional for master)
}

byte x = 0;

void loop()
{
  Wire.beginTransmission(4);  // transmit to device #4
  Wire.write(x);              // sends one byte  
  Wire.endTransmission();     // stop transmitting

  x++;
  delay(500);
}

• Code of the Slave :

// Wire Slave Receiver
#include <Wire.h>

void setup()
{
  Wire.begin(4);                // join i2c bus with address #4
  Wire.onReceive(receiveEvent); // register event
  
  Serial.begin(9600);           
}

void loop(){  delay(100);}

void receiveEvent(int howMany)
{
  x = Wire.read();              // receive byte
  
  Serial.println(x);         
}