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 Dontronics 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 Dontronics 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.