IICBUS(4)						   BSD Kernel Interfaces Manual 						 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 architecture-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 address 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 initiates 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 before, 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 receive 8-bit characters they write to the bus according to the I2C protocol.

     I2C interfaces may act on the bus as slave devices, allowing spontaneous bidirectional communications, thanks to the multi-master capabili-
     ties 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 interface
     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