For this demonstration, I used an I2C connection between two Arduino UNO boards. Let’s construct a simple circuit to show how I2C in Arduino works. The ATmega328P microcontroller found in the Arduino UNO and Nano is capable of I2C data transfer rates of up to 400 kilohertz. The following table summarises the I2C pin configurations of the most common Arduino boards and should prove useful if you’re working with a different board. The original Arduino UNO’s revision 3 added SDA and SCL pins near Digital IO Pin 13 (near the USB socket).

To communicate with other devices using SDA and SCL, use the A4 and A5 pins, respectively. Analog Input pins A4 and A5 have the additional function of I2C, as detailed in the “ARDUINO UNO PINOUT” tutorial for the Arduino UNO. I2C communication is supported by Arduino. Using this address, the master can choose a specific slave to send or receive data from, and the slave will respond appropriately. There is a unique 7-bit address for each slave device on the I2C bus. It is possible to have both multiple masters and multiple slaves on an I2C network (but we usually see single master and multiple slaves).

The master also provides the clock signal. It is the job of the Bus Master to transmit and receive data to and from the slave devices. I2C Bus devices can be either “Master” or “Slave,” depending on their connection type.

Wire library read from