I²C

I²C
Name	I²C
Caption	Two-wire serial bus topology
Inventors	Philips Semiconductor
Introduced	1980s
Type	Synchronous serial communication

I²C I²C is a two-wire, synchronous, multi-master serial communication bus widely used for short-distance communication between integrated circuits. Developed for embedded systems, it enables microcontrollers, sensors, memory devices, and peripherals to exchange control and configuration data using a serial clock and data line. The specification influenced numerous embedded platforms and ecosystems across consumer electronics, industrial automation, and computing.

History

The bus emerged in the mid-1980s at Philips to simplify board-level communications among components in products by Philips Semiconductor engineers. Early commercial adoption occurred in devices from Sony, Panasonic, and Toshiba, while standards and silicon support expanded through collaborations with firms such as Intel, Motorola, Texas Instruments, and STMicroelectronics. As embedded computing grew, institutions like MIT, Stanford University, and Carnegie Mellon University used the bus in research platforms, while consumer brands including Apple Inc., Samsung Electronics, LG Electronics, Sharp Corporation, and Panasonic Corporation integrated it into electronics. The architecture influenced later buses and standards from organizations such as JEDEC, IEEE, and USB-IF, and it featured in products by Nokia, Ericsson, Siemens, Alcatel-Lucent, and Huawei Technologies. Over decades, academic laboratories at Caltech, Harvard University, and University of Cambridge examined protocols including this bus alongside alternatives from IBM, Bell Labs, and AT&T Bell Laboratories.

Technical overview

The bus uses two bidirectional open-drain lines: Serial Data and Serial Clock. Designers at Philips Semiconductor prioritized minimal pin count and simple arbitration to allow multiple masters like microcontrollers from Microchip Technology, NXP Semiconductors, Analog Devices, Renesas Electronics, and Infineon Technologies to coexist on a single pair of wires. Common devices on the bus include EEPROMs from Microchip Technology and Atmel Corporation, real-time clocks by Seiko Instruments and Maxim Integrated, ADCs from Analog Devices and Texas Instruments, and sensors by Bosch Sensortec, STMicroelectronics, and InvenSense. Embedded platforms and single-board computers such as Raspberry Pi, BeagleBoard, Arduino, Intel Edison, and NVIDIA Jetson expose host interfaces compatible with the bus. Standards bodies and consortia including JEDEC Solid State Technology Association and corporate implementers maintained interoperability through datasheets published by vendors like Samsung, Panasonic, Toshiba, and Micron Technology.

Protocol and signaling

Communication is framed into START, STOP, and ACK/NACK conditions transmitted on the data line while synchronized to the clock line generated by master controllers such as microprocessors from ARM Holdings, Intel Corporation, AMD, Qualcomm, and Broadcom. Arbitration resolves bus contention deterministically, permitting masters from NXP and Renesas to compete without data corruption. The protocol uses 7-bit and 10-bit addressing modes that device manufacturers including Maxim Integrated, Linear Technology, Cirrus Logic, and Analog Devices implement in silicon. Timing modes—Standard, Fast, Fast-mode Plus, and High-speed—were adopted and documented by vendors including STMicroelectronics, Texas Instruments, Microchip Technology, and ON Semiconductor to accommodate different clock rates and DUTs used in products by Sony, Canon, Nikon, and GoPro.

Electrical characteristics

The bus relies on pull-up resistors to VCC and open-drain/open-collector drivers implemented in ICs from NXP Semiconductors, STMicroelectronics, Texas Instruments, and Infineon Technologies. Voltage levels span common logic families such as TTL and CMOS, with supply domains found in devices by ARM, Intel, Qualcomm, Broadcom, and Mediatek determining compatibility. Signal integrity considerations lead system designers at Bosch, Siemens, ABB, Schneider Electric, and Rockwell Automation to specify pull-up values, bus capacitance, and board layout practices. Vendors such as Rohm Semiconductor, Toshiba, Renesas, and Maxim Integrated provide application notes covering ESD protection, noise margins, and level shifting when interfacing components produced by Samsung Electronics, Micron Technology, and SK Hynix.

Addressing and data formats

Addressing schemes include 7-bit and 10-bit formats standardized in vendor datasheets from NXP, STMicroelectronics, Texas Instruments, and Microchip Technology. Common peripheral address assignments appear in modules from Bosch Sensortec, InvenSense, Maxim Integrated, and Analog Devices for sensors, and in memory products from Atmel, Microchip Technology, and STMicroelectronics. Data framing typically uses 8-bit bytes with MSB-first ordering as implemented by microcontroller cores from ARM, Microchip, Atmel/Microchip, Renesas, and Espressif Systems. Protocol extensions and reserved addresses are handled in silicon from NXP, Analog Devices, TI, and STMicroelectronics and documented by standards groups and manufacturers like Sony, Panasonic, and Toshiba.

Implementations and variants

Commercial IP and silicon implementations appear across product lines from NXP Semiconductors, STMicroelectronics, Texas Instruments, Microchip Technology, and Analog Devices. Variants and related buses—pioneered or adapted by companies such as Intel, AMD, ARM Holdings, Xilinx, and Altera—include SMBus and PMBus with governance by groups like Intel Corporation, SMBus Working Group, and power-management teams at Dell Technologies, HP Inc., and Lenovo. High-speed and multiplexed adaptations have been produced by NVIDIA, Qualcomm, Broadcom, and Samsung for advanced SoC interconnects. Open-source software stacks and drivers in projects maintained by Linux Foundation, Debian Project, Ubuntu, Arduino Project, and Raspberry Pi Foundation provide broad platform support.

Applications and interoperability

The bus is ubiquitous in embedded control, sensing, configuration, and board management for products by Apple Inc., Dell Technologies, HP Inc., Lenovo, Asus, and Acer Inc.. In automotive and industrial systems, suppliers like Bosch, Continental AG, Denso, Delphi Technologies, and Valeo use the bus for sensor networks and subsystem configuration. Consumer electronics manufacturers including Samsung Electronics, Sony, LG Electronics, Panasonic Corporation, and Sharp Corporation use it for display control, camera modules, and power management. Interoperability efforts by standards organizations and silicon vendors—JEDEC, IEEE, Linux Foundation, NXP, and STMicroelectronics—ensure devices from disparate manufacturers interoperate across platforms like Raspberry Pi, BeagleBoard, Arduino, and enterprise systems from IBM and Dell EMC.

Category:Computer buses