DragonFly On-Line Manual Pages
IICBUS(4) DragonFly Kernel Interfaces Manual IICBUS(4)
iicbus -- I2C bus system
The iicbus system provides a uniform, modular and architecture-indepen-
dent system for the implementation of drivers to control various I2C
devices and to utilize different I2C controllers.
I2C is an acronym for Inter Integrated Circuit bus. The I2C bus was
developed in the early 1980's by Philips semiconductors. It's purpose
was to provide an easy way to connect a CPU to peripheral chips in a TV-
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 function-
ality. 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.
Some I2C device drivers are available:
iic general i/o operation
ic network IP interface
iicsmb I2C to SMB software bridge
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 capabilities of
the I2C protocol.
Some I2C interfaces are available:
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
iicbb(4), lpbb(4), pcf(4)
The iicbus manual page first appeared in FreeBSD 3.0.
This manual page was written by Nicolas Souchu.
DragonFly 4.9 August 6, 1998 DragonFly 4.9