1 =============================
2 Introduction to I2C and SMBus
3 =============================
4
5 I²C (pronounce: I squared C and written I2C i
6 a protocol developed by Philips. It is a two-w
7 speed (typically up to 400 kHz, high speed mod
8 an inexpensive bus for connecting many types o
9 low bandwidth communications needs. I2C is wid
10 systems. Some systems use variants that don't
11 and so are not advertised as being I2C but com
12 e.g. TWI (Two Wire Interface), IIC.
13
14 The latest official I2C specification is the `
15 manual" (UM10204) <https://www.nxp.com/docs/en
16 published by NXP Semiconductors, version 7 as
17
18 SMBus (System Management Bus) is based on the
19 a subset of I2C protocols and signaling. Many
20 SMBus, but some SMBus protocols add semantics
21 achieve I2C branding. Modern PC mainboards rel
22 devices connected through SMBus are RAM module
23 and hardware monitoring chips.
24
25 Because the SMBus is mostly a subset of the ge
26 use its protocols on many I2C systems. However
27 meet both SMBus and I2C electrical constraints
28 implement all the common SMBus protocol semant
29
30
31 Terminology
32 ===========
33
34 The I2C bus connects one or more controller ch
35
36 .. kernel-figure:: i2c_bus.svg
37 :alt: Simple I2C bus with one controller
38
39 Simple I2C bus
40
41 A **controller** chip is a node that starts co
42 Linux kernel implementation it is also called
43 drivers are usually in the ``drivers/i2c/busse
44
45 An **algorithm** contains general code that ca
46 class of I2C controllers. Each specific contro
47 algorithm driver in the ``drivers/i2c/algos/``
48 own implementation.
49
50 A **target** chip is a node that responds to c
51 controller. In the Linux kernel implementation
52 While targets are usually separate external ch
53 target (needs hardware support) and respond to
54 This is then called a **local target**. In con
55 a **remote target**.
56
57 Target drivers are kept in a directory specifi
58 for example ``drivers/gpio/`` for GPIO expande
59 video-related chips.
60
61 For the example configuration in the figure ab
62 the I2C controller, and drivers for your I2C t
63 each target.
64
65 Synonyms
66 --------
67
68 As mentioned above, the Linux I2C implementati
69 "adapter" for controller and "client" for targ
70 have these synonyms in their name. So, when di
71 you should be aware of these terms as well. Th
72 though.
73
74 Outdated terminology
75 --------------------
76
77 In earlier I2C specifications, controller was
78 named "slave". These terms have been obsoleted
79 their use is also discouraged by the Linux Ker
80 still find them in references to documentation
81 general attitude, however, is to use the inclu
82 target. Work to replace the old terminology in
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