It's not even technical. It's philosophical! I've often said, "where you sit determines what you see," which is an old military addage. You and I see things from very different vantage points. I've never intended to impugn your motives, though I've sometimes questioned the rationale.

While it's easy to see things on a personal basis, you could see, if you'd stop focusing on "being right" and, instead, try to see what's being said to you, that it's about modfying your stance.

I'm worried about that 8 MHz MCU to which you keep referring, and I'm wondering why it is you think the 8255 would be too slow for so many tasks. I believe you've forgotten, or perhaps never read, and more certainly never understood, what's in the 8255 datasheet. Further, you keep saying it's too slow, yet each time you propose a solution, it's nearly always one that can't match the capability of the 8255.

As I've said, I'm not a lover of the 8255, but I am a lover of truth and accuracy in representing what can be done. This doesn't say that it SHOULD be done, and certainly not in all cases. I think you're so focused on being "right" that you've ignored some of the facts.

Yes, the 8255's been around a long time, and, yes, it's a relatively slow part for use with modern 4-clockers at rates of 16 MHz and above. However, it's still possible to exploit this device. If it didn't have a place, would anyone still be making it? There are, I'm sure, plenty of unpackaged dice of lots of old parts in storage they'd not be taking up fab space and time if there weren't a market.

About the relative cost of the MCU's you use, though, I wonder how much time you took to justify using the fanciest, most costly MCU available. Do you really need to operate at 100 MIPS? Would it be just as effective if you operated at 33 MIPS? Wouldn't the slower version of the MCU cost less? What cost comparisons did you make? What sort of performance analysis did you go thorough? If you went through a thorough analysis of the performance requirements, I wonder how you did that. How did you determine the baseline system clock rate requirement? The process might be of interest to everyone.

RE