I2C (Inter-Integrated Circuit) is a two wire serial interface usually used for on-board low-speed bi-directional communication between controllers and peripherals. The master device is responsible for initiating and controlling all transfers on the I2C bus. Only one master device can be active on the I2C bus at the time, but the master role can be transferred between devices on the same I2C bus. I2C uses only two bidirectional open-drain lines, usually designated SDA (Serial Data Line) and SCL (Serial Clock Line), with pull up resistors.