Wait a minute, here ... It's not fair to tell him he's using the wrong device or taking the wrong approach when he hasn't defined either one yet.

This is an exercise encountered in every logic circuits (EE 101) course, though, and he should complete the course before getting into this. Now, if there are published notes on how to do this, then perhaps he should be given the opportunity to examine them.

He's been scored for poorly/inadequately described requirements. That's a common failure. However, he's stated he wants information that will let him learn how to decode addresses. So many stupid, Stupid, STUPID applications with the 805x are published every year because people haven't learned how to do this. It's not rocket-science, though you'd think so, as so few designs that appear in this forum use it. It's true, if you have to add lots of external I/O hardware, you're probably using the wrong part, but if a guy wants to learn, and isn't planning to go to production, he should certainly learn how this stuff works.

Yes, there are parts that do the address decoding for you, but the reason there are so many variations on the original 805x is because there are so many integrated peripherals. If you like one, then you use it, but if you're trying to learn the 8052, keep in mind that it doesn't have address decoding, and doesn't have ADC/DAC hardware, and doesn't have a lot of XRAM, or, for that matter, a lot of code memory. If a fellow wants to learn how to build an "expanded" system on the 8052, then let's let him do that before we slap him down for doing what someone else wouldn't dom and, instead, help him learn what he wants to learn.

RE