This presumption that there's something "WRONG" with using an 8255 is fallacious. The groundwork has not been presented, i.e. define "wrong," present specifics.

There have been lots of "handwaves" about what's wrong with the 8255, but I've yet to see even ONE precise example of how to replace an 8255 with something equally effective.

Many of the arguments that have been presented against the use of this venerable IC have been more or less correct, in one sense or another, but none have been complete.

Several of the "too fast" 805x variants have the means for opeating their external memory bus at speeds compatible with even the slowest (~450 ns) 8255's, while others require the faster (~250 ns) parts.

Plenty of arguments, mostly based in practical reality, have been presented by those who wish to use the 8255.

My interest in this matter has not been to promote the 8255's use, but to stop the stupid, Stupid, STUPID practice of telling someone, "No! Don't do that!" when they don't know why the O/P wants to use them. It certainly makes no sense to tell someone not to do that, if it's their job, or if it's their assignment.

While it's true that, for any given application, there are probably better ways to do things, it makes no sense to tell a student, whose assignment is to use the 8255 that's on the board that his instructor told him to buy, that it's a mistake to use it. It also makes little sense to tell each and every one who asks about how to do something, ... anything, that he shouldn't do that. It's like telling someone, who's asked for the time of day, how to build a clock. When you're done, you've wasted your time and his, yet he still doesn't know what time it is.

What's needed in this FAQ is NOT an assertion of something that's not proveable, namely that something's wrong with the 8255, but sufficient examples to answer the questions without a 50+ post-long thread of tirades from people who've never used the thing.

The latter observation applies not just to the many comments about the 8255, but to every question that's addressed in this forum. It's important the we focus on answering questions, and not just on pontificating about our unfounded beliefs.

RE