Parallel Port Adapters
----------------------
If you are installing parallel port adapters it means you are probably messing 
around with wires and IC's and the like. If you have purchased a card that 
provides an external i2c/smbus this will require combined algorithm and 
adapter code in a single module.
If you are doing it yourself by using the parallel port there 
are basically 2 options.

1) Using the parallel port and using the i2c-pport adapter module and the 
i2c-algo-bit algorithm module together to enable you to wire up your parallel 
port to act as an i2c/smbus. This provides a bus that will enable most 
sensors to work but doesn't support the entire i2c/smbus capability.

2) Using the parallel port to interface to a Philips PCF8584 parallel to i2c 
adapter chip. You will need to build a bit of a circuit to do this. This 
configuration needs the i2c-pcf-epp adapter module and the i2c-algo-pcf 
algorithm module. This support almost all of the i2c/smbus capabilities.


i2c-pport Documentation
-----------------------
This is a primitive parallel port driver for the i2c bus, which exploits 
features of modern bidirectional parallel ports. 

Bidirectional ports have particular bits connected in following way:
   
                        |
            /-----|     R
         --o|     |-----|
      read  \-----|     /------- Out pin
                      |/
                   - -|\
                write   V
                        |
                       ---  


It means when output is set to 1 we can read the port. Therefore 
we can use 2 pins of parallel port as SDA and SCL for i2c bus. It 
is not necessary to add any external - additional parts, we can 
read and write the same port simultaneously.
	I only use register base+2 so it is possible to use all 
8 data bits of parallel port for other applications (I have 
connected EEPROM and LCD display). I do not use bit Enable Bi-directional
 Port. The only disadvantage is we can only support 5V chips.

Layout:

Cannon 25 pin

SDA - connect to pin 14 (Auto Linefeed)
SCL - connect to pin 16 (Initialize Printer)
GND - connect to pin 18-25
+5V - use external supply (I use 5V from 3.5" floppy connector)
      
no pullups  requied

Module parameters:

base = 0xXXX
XXX - 278 or 378

That's all.

Daniel Smolik
marvin@sitour.cz
