Inter Integrated Circuit
The Inter-Integrated Circuit (I2C) Protocol is a protocol intended to allow multiple "peripheral" digital integrated circuits ("chips") to communicate with one or more "controller" chips.
I2C was originally developed in 1982 by Philips for various Philips chips.
Each I2C bus consists of two signals: SDA and SCL. SDA (Serial Data) is the data signal and SCL (Serial Clock) is the clock signal. The clock signal is always generated by the current bus controller
Messages are broken up into two types of frame: an address frame, where the controller indicates the peripheral to which the message is being sent, and one or more data frames, which are 8-bit data messages passed from controller to peripheral or vice versa. Data is placed on the SDA line after SCL goes low, and is sampled after the SCL line goes high. The time between clock edge and data read/write is defined by the devices on the bus and will vary from chip to chip.