Skip site navigation (1)Skip section navigation (2)

FreeBSD Manual Pages


home | help
IICBUS(4)              FreeBSD Kernel Interfaces Manual              IICBUS(4)

     iicbus -- I2C bus system

     device iicbus
     device iicbb

     device iic
     device ic
     device iicsmb

     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.  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 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:

     Devices           Description
     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:

     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

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

     The iicbus manual page first appeared in FreeBSD 3.0.

     This manual page was written by Nicolas Souchu.

FreeBSD 6.2                     August 6, 1998                     FreeBSD 6.2


Want to link to this manual page? Use this URL:

home | help