I2C
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I2C (Inter-Integrated Circuit; pronounced as "eye-squared-see" or "eye-two-see"), alternatively known as I2C and IIC, is a synchronous, multi-master/multi-slave, single-ended, serial communication bus invented in 1980 by Philips Semiconductors (now NXP Semiconductors). It is widely used for attaching lower-speed peripheral integrated circuits (ICs) to processors and microcontrollers in short-distance, intra-board communication.
In the European Patent EP0051332B1 Ad P.M.M. Moelands and Herman Schutte are named as inventors of the I2C bus. Both were working in 1980 as development engineers in the central application laboratory CAB of Philips in Eindhoven where the I2C bus was developed as "Two-wire bus-system comprising a clock wire and a data wire for interconnecting a number of stations". The US patent was granted under number US4689740A. The internal development name of the bus was first COMIC which was later changed to I2C. The patent was transferred by both gentlemen to Koninklijke Philips NV.
The I2C bus can be found in a wide range of electronics applications where simplicity and low manufacturing cost are more important than speed. PC components and systems which involve I2C include serial presence detect (SPD) EEPROMs on dual in-line memory modules (DIMMs) and Extended Display Identification Data (EDID) for monitors via VGA, DVI, and HDMI connectors. Common I2C applications include reading hardware monitors, sensors, real-time clocks, controlling actuators, accessing low-speed DACs and ADCs, controlling simple LCD or OLED displays, changing computer display settings (e.g., backlight, contrast, hue, color balance) via Display Data Channel, and changing speaker volume.
A particular strength of I2C is the capability of a microcontroller to control a network of device chips with just two general-purpose I/O pins and software. Many other bus technologies used in similar applications, such as Serial Peripheral Interface Bus (SPI), require more pins and signals to connect multiple devices.
System Management Bus (SMBus), defined by Intel and Duracell in 1994, is a subset of I2C, defining a stricter usage. One purpose of SMBus is to promote robustness and interoperability. Accordingly, modern I2C systems incorporate some policies and rules from SMBus, sometimes supporting both I2C and SMBus, requiring only minimal reconfiguration either by commanding or output pin use. System management for PC systems uses SMBus whose pins are allocated in both conventional PCI and PCI Express connectors.
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