It's not clear to me what you mean by "8 MHz part" or "12 MHz part," and if it's not clear to me, it certainly won't be clear to a student. You see, the notion of an "8 MHz part" with respect to the i8255, means one thing, while "12 MHz part" with respect to an 805x means something quite different.

I referred to the attainable clock speeds for classic '51s connected to 8255s. I really do not care if that is clear to a student since it refer to history, not current design practices. No student should be exposed to the 8255 as "something to learn", were I to teach a microcontroller course, I might mention it as "look at this if you are interested in how thing were in the olden days" nothing beyond that.

Erik

Richard, you post regularily "stick to the subject", fair enough, but when teaching is involved I consider these issues much more critical.