It is possible that your 8255 is dead or you didn't wire it properly when you hooked it up. I would...

- Check every wire

- Make sure the external bus interface of your processor is setup correct.

- Make sure read and write strobes to the 8255 are setup properly.

- Make sure the data bus is wired in the correct bit order.


I have seen many a engineer that spent a long time debugging a chip hooked to a bus only to discover after many hours of work that the bus is connected on the wrong order. And of course when the bits are not in the right order, then any initialization and control words you send to the chip make no correct sense to the chip.

Michael Karas