Inter-Integrated Circuit is a synchronous, multi-master, multi-slave packet switched serial bus. It uses only two bidirectional open-drain lines, Serial Data and Serial Clock, pulled up with resistors. Designers use it extensively to attach sensors, EEPROMs, and real-time clocks to microcontrollers because it requires minimal pin count and traces on the printed circuit board.
Check the pull-up resistors on the I²C bus, the clock line looks like a shark fin instead of a square wave.
Do not mix it up with
- SPI: I²C uses two wires and supports multiple masters, while SPI uses four wires and is strictly single-master but operates at much higher speeds.
Related terms
SPI
Serial Peripheral Interface, a synchronous serial communication protocol for short-distance data transfer.
UART
A universal asynchronous receiver-transmitter is a hardware block that translates data between parallel and serial forms.
Pull-up resistor
A resistor connected between a logic pin and a positive supply voltage to hold the line at a logic high state.
Clock
A continuous square wave signal that synchronizes the timing of digital circuits.