I2C? is a 2-wire serial interface developed by Philips Semiconductor, now NXP Semiconductors. The bus consists of a data line (SDA) and a clock line (SCL) with pullup structures. When the bus is idle, both SDA and SCL lines are pulled high. All the I²C-compatible devices connect to the I²C bus through open drain I/O pins, SDA and SCL. A controller device, usually a microcontroller or a digital signal processor, controls the bus. The controller is responsible for generating the SCL signal and device addresses. The controller also generates specific conditions that indicate the START and STOP of data transfer. A target device receives or transmits data on the bus under control of the controller device, or both.

The device works as a target and supports the following data transfer modes, as defined in the I²C-Bus Specification: standard mode (100 kbps) and fast mode (400 kbps), fast mode plus (1 Mbps), and high-speed mode (3.4 Mbps). The interface adds flexibility to the power supply solution, enabling most functions to be programmed to new values depending on the instantaneous application requirements. Register contents remain intact as long as the input voltage remains above 1.8 V.

The data transfer protocol for standard and fast modes is exactly the same, therefore, they are referred to as F/S-mode in this document. The protocol for high-speed mode is different from F/S-mode, and it is referred to as HS-mode.

It is recommended that the I²C controller initiates a STOP condition on the I²C bus after the initial power up of SDA and SCL pullup voltages to ensure reset of the I²C engine.