iicbus(4)

NAME

iicbus - I2C bus system

SYNOPSIS

device iicbus
device iicbb
device iic
device ic
device iicsmb

DESCRIPTION

The iicbus system provides a uniform, modular and architec

ture-independent system for the implementation of drivers to control

various I2C
devices and to utilize different I2C controllers.

I2C

I2C is an acronym for Inter Integrated Circuit bus. The I2C

bus was
developed in the early 1980's by Philips semiconductors.

Its purpose was
to provide an easy way to connect a CPU to peripheral chips

in a TV-set.

The BUS physically consists of 2 active wires and a ground

connection.
The active wires, SDA and SCL, are both bidirectional.

Where SDA is the
Serial DAta line and SCL is the Serial CLock line.

Every component hooked up to the bus has its own unique ad

dress whether
it is a CPU, LCD driver, memory, or complex function chip.

Each of these
chips can act as a receiver and/or transmitter depending on

its functionality. Obviously an LCD driver is only a receiver, while a

memory or I/O
chip can both be transmitter and receiver. Furthermore

there may be one
or more BUS MASTERs.

The BUS MASTER is the chip issuing the commands on the BUS.

In the I2C
protocol specification it is stated that the IC that initi

ates a data
transfer on the bus is considered the BUS MASTER. At that

time all the
others are regarded to as the BUS SLAVEs. As mentioned be

fore, the IC
bus is a Multi-MASTER BUS. This means that more than one IC

capable of
initiating data transfer can be connected to it.

DEVICES

Some I2C device drivers are available:

Devices Description
iic general i/o operation
ic network IP interface
iicsmb I2C to SMB software bridge

INTERFACES

The I2C protocol may be implemented by hardware or software.

Software
interfaces rely on very simple hardware, usually two lines

twiddled by 2
registers. Hardware interfaces are more intelligent and re

ceive 8-bit
characters they write to the bus according to the I2C proto

col.

I2C interfaces may act on the bus as slave devices, allowing

spontaneous
bidirectional communications, thanks to the multi-master ca

pabilities of
the I2C protocol.

Some I2C interfaces are available:

Interface Description pcf Philips PCF8584 master/slave interface
iicbb generic bit-banging master-only driver
lpbb parallel port specific bit-banging in

terface
bktr Brooktree848 video chipset, hardware

and software

master-only interface

SEE ALSO

iicbb(4), lpbb(4), pcf(4)

HISTORY

The iicbus manual page first appeared in FreeBSD 3.0.

AUTHORS

This manual page was written by Nicolas Souchu.

BSD August 6, 1998

BSD