It is uses I²C (Inter-Integrated Circuit) protocol, referred to as I-squared-C, I-two-C, or IIC) for communication with the micrcontroller.Let see first the basics of the communication protocol first.
The I²C require only two wires for communication. One is called the Serial Data (SDA) and the other is Serial Clock (SCL) as shown.
There are various modes and configurations in which it can be used. Let us start simply with a single master and a single slave.
The Master generates the clock for serial communicaton