Documentation/i2c/summary.rst

2 Introduction to I2C and SMBus
5 I²C (pronounce: I squared C and written I2C in the kernel documentation) is
6 a protocol developed by Philips. It is a slow two-wire protocol (variable
8 an inexpensive bus for connecting many types of devices with infrequent or
9 low bandwidth communications needs.  I2C is widely used with embedded
11 and so are not advertised as being I2C but come under different names,
14 The latest official I2C specification is the `"I2C-bus specification and user
16 published by NXP Semiconductors. However, you need to log-in to the site to
18 `here <https://web.archive.org/web/20210813122132/https://www.nxp.com/docs/en/user-guide/UM10204.pd…
20 SMBus (System Management Bus) is based on the I2C protocol, and is mostly
21 a subset of I2C protocols and signaling.  Many I2C devices will work on an
23 achieve I2C branding.  Modern PC mainboards rely on SMBus.  The most common
24 devices connected through SMBus are RAM modules configured using I2C EEPROMs,
27 Because the SMBus is mostly a subset of the generalized I2C bus, we can
28 use its protocols on many I2C systems.  However, there are systems that don't
29 meet both SMBus and I2C electrical constraints; and others which can't
36 Using the terminology from the official documentation, the I2C bus connects
39 .. kernel-figure::  i2c_bus.svg
40    :alt:    Simple I2C bus with one master and 3 slaves
42    Simple I2C bus
45 Linux kernel implementation it is called an **adapter** or bus. Adapter
46 drivers are in the ``drivers/i2c/busses/`` subdirectory.
49 whole class of I2C adapters. Each specific adapter driver either depends on
50 an algorithm driver in the ``drivers/i2c/algos/`` subdirectory, or includes
56 ``drivers/media/gpio/`` for GPIO expanders and ``drivers/media/i2c/`` for
57 video-related chips.
60 I2C adapter, and drivers for your I2C devices (usually one driver for each