1 Primitive parallel port is driver for i2c bus, which exploits
2 features of modern bidirectional parallel ports.
4 Bidirectional ports have particular bits connected in following way:
9 read \-----| /------- Out pin
17 It means when output is set to 1 we can read the port. Therefore
18 we can use 2 pins of parallel port as SDA and SCL for i2c bus. It
19 is not necessary to add any external - additional parts, we can
20 read and write the same port simultaneously.
21 I only use register base+2 so it is possible to use all
22 8 data bits of parallel port for other applications (I have
23 connected EEPROM and LCD display). I do not use bit Enable Bi-directional
24 Port. The only disadvantage is we can only support 5V chips.
30 SDA - connect to pin 14 (Auto Linefeed)
31 SCL - connect to pin 16 (Initialize Printer)
32 GND - connect to pin 18-25
33 +5V - use external supply (I use 5V from 3.5" floppy connector)