Documentation/i2c/busses/i2c-parport.rst

Source file repositories/reference/linux-study-clean/Documentation/i2c/busses/i2c-parport.rst

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Documentation/i2c/busses/i2c-parport.rst
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=========================
Kernel driver i2c-parport
=========================

Author: Jean Delvare <jdelvare@suse.de>

This is a unified driver for several i2c-over-parallel-port adapters,
such as the ones made by Philips, Velleman or ELV. This driver is
meant as a replacement for the older, individual drivers:

 * i2c-philips-par
 * i2c-elv
 * i2c-velleman
 * video/i2c-parport
   (NOT the same as this one, dedicated to home brew teletext adapters)

It currently supports the following devices:

 * (type=0) Philips adapter
 * (type=1) home brew teletext adapter
 * (type=2) Velleman K8000 adapter
 * (type=3) ELV adapter
 * (type=4) Analog Devices ADM1032 evaluation board
 * (type=5) Analog Devices evaluation boards: ADM1025, ADM1030, ADM1031
 * (type=6) Barco LPT->DVI (K5800236) adapter
 * (type=7) One For All JP1 parallel port adapter
 * (type=8) VCT-jig

These devices use different pinout configurations, so you have to tell
the driver what you have, using the type module parameter. There is no
way to autodetect the devices. Support for different pinout configurations
can be easily added when needed.

Earlier kernels defaulted to type=0 (Philips).  But now, if the type
parameter is missing, the driver will simply fail to initialize.

SMBus alert support is available on adapters which have this line properly
connected to the parallel port's interrupt pin.


Building your own adapter
-------------------------

If you want to build you own i2c-over-parallel-port adapter, here is
a sample electronics schema (credits go to Sylvain Munaut)::

  Device                                                      PC
  Side          ___________________Vdd (+)                    Side
                 |    |         |
                ---  ---       ---
                | |  | |       | |
                |R|  |R|       |R|
                | |  | |       | |
                ---  ---       ---
                 |    |         |
                 |    |    /|   |
  SCL  ----------x--------o |-----------x-------------------  pin 2
                      |    \|   |       |
                      |         |       |
                      |   |\    |       |
  SDA  ----------x----x---| o---x---------------------------  pin 13
                 |        |/            |
                 |                      |
                 |         /|           |
                 ---------o |----------------x--------------  pin 3
                           \|           |    |
                                        |    |
                                       ---  ---
                                       | |  | |
                                       |R|  |R|

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Implementation Notes