The fact that many professors teach with example circuits that use 8255 chips is rather unfortunate. In my humble opinion it reflects on the laziness of the professors to modernize their course materials.

There are also a whole flurry of "learning electronics" books that are stuffed with 8255 design examples.

All these are a carry over from the historical time when a microprocessor chip had a bus on it. I can recall dozens of processor part numbers from over the years where to get parallel ports you used an 8255 becasue it was almost a single chip solution. We can recall 8080, Z80, 2650, 1802, 6502, 8085, 6303, 6800, 68HC11 and on and on....

These days the newest chips have almost all (if not all) of the memory you need right on-board and so there is really no need to do a bus in most embedded designs. (Particularly ones where 8051 architecture type parts are attractive). Heck I have found that with even a graphics LCD controller it is almost better to use a serial interface hook up to the things instead of trying to "bus connect" the thing to a 8051 derative type processor.

Eliminating the bus, as Erik has pointed out here time and again, gives you back a lot of I/O. And using the newest parts with the onboard memory will lead to lowest overall system cost despite the fact that these newer & nicer parts seem to cost a whole lot more than the old 80C32 chip.

Michael Karas