When using the parallel port for interfacing projects I often encountered the problem of insufficient io lines. To overcome this problem I designed an 8255 parallel port expander. To use this expander your parallel port needs to be bi-directional.

Circuit diagram of 8255 parallel port expander.
 
 

PCB layout.
 
 

Component overlay.
 
 

Photo of populated PCB.
 
 

Prototype board used to jumper 8255 port A & B lines to a DT203 switch led board. Port A is connected to the Leds and port B is connected to the switches.
 
 

8255 expander board connected to a computer & switch/led test board.
 
 

Close up of 8255 to DT004 & DT203 connection.
 

Having made the parallel port expansion board it occured that it could also be used in conjunction with a DT004 to expand the io lines for AT89Cx051.

Victoria University
Electronics Department
Peter Averill
23 May 1999

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