1 .\" Copyright (c) 1998, Nicolas Souchu
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35 .Cd "controller iicbus0"
36 .Cd "controller iicbb0"
38 .Cd "device iic0 at iicbus?"
39 .Cd "device ic0 at iicbus?"
40 .Cd "device iicsmb0 at iicbus?"
44 system provides a uniform, modular and architecture-independent
45 system for the implementation of drivers to control various I2C devices
46 and to utilize different I2C controllers.
48 I2C is an acronym for Inter Integrated Circuit bus. The I2C bus was developed
49 in the early 1980's by Philips semiconductors. It's purpose was to provide an
50 easy way to connect a CPU to peripheral chips in a TV-set.
52 The BUS physically consists of 2 active wires and a ground connection.
53 The active wires, SDA and SCL, are both bidirectional. Where SDA is the
54 Serial DAta line and SCL is the Serial CLock line.
56 Every component hooked up to the bus has its own unique address whether it
57 is a CPU, LCD driver, memory, or complex function chip. Each of these chips
58 can act as a receiver and/or transmitter depending on it's functionality.
59 Obviously an LCD driver is only a receiver, while a memory or I/O chip can
60 both be transmitter and receiver. Furthermore there may be one or
63 The BUS MASTER is the chip issuing the commands on the BUS. In the I2C protocol
64 specification it is stated that the IC that initiates a data transfer on the
65 bus is considered the BUS MASTER. At that time all the others are regarded to
66 as the BUS SLAVEs. As mentioned before, the IC bus is a Multi-MASTER BUS.
67 This means that more than one IC capable of initiating data transfer can be
70 Some I2C device drivers are available:
72 .Bl -column "Device drivers" -compact
73 .It Em Devices Ta Em Description
74 .It Sy iic Ta "general i/o operation"
75 .It Sy ic Ta "network IP interface"
76 .It Sy iicsmb Ta "I2C to SMB software bridge"
79 The I2C protocol may be implemented by hardware or software. Software
80 interfaces rely on very simple hardware, usually two lines
81 twiddled by 2 registers. Hardware interfaces are more intelligent and receive
82 8-bit characters they write to the bus according to the I2C protocol.
84 I2C interfaces may act on the bus as slave devices, allowing spontaneous
85 bidirectional communications, thanks to the mutli-master capabilities of the
88 Some I2C interfaces are available:
90 .Bl -column "Interface drivers" -compact
91 .It Em Interface Ta Em Description
92 .It Sy pcf Ta "Philips PCF8584 master/slave interface"
93 .It Sy iicbb Ta "generic bit-banging master-only driver"
94 .It Sy lpbb Ta "parallel port specific bit-banging interface"
95 .It Sy bktr Ta "Brooktree848 video chipset, hardware and software master-only interface"
104 manual page first appeared in
108 manual page was written by