A common reaction to "please help me do this ..." is "why would you want to do it that way?" I believe this is basically wrong, because there's a lot of learning contained in doing it "that" way rather than coming up with a new way.

I've nagged and nagged at people to stop telling the O/P to make it round when he clearly wants it square. Modern technology may suggest that round will roll better, but if he wants it square, that's how it should be, and there's nothing to make it better if it's round when he wants it square.

In this particular case, the O/P explained, perhaps not quite adequately, that he needed help with making an 8155 work. Apparently his operating environment was the old ROM BASIC. I conclude this from the apparent reversal of the address lines from the data lines, which I've seen in a Basic52 application at some time. This was originally done to facilitate PCB layout, and the ROM/EPROM has found its way into wide distribution. It could, of course, be corrected, as it's just a wiring issue, but for some reason, the O/P wants to deal with it as-is.

It is not only possible but often desirable to make a circuit such as the one proposed work quite adequately, Erik's somewhat exaggerated comments about performance aside.

When someone asks you what time it is, you shouldn't tell him how to build a clock. When you're finished, he still doesn't know what time it is. I think there's far too much of that in this forum.

When your boss, an engineer with many years' experience, tells you to build a circuit with THESE components, do you tell him, "Oh, but it would be much better to use these ..." or some such? He'd likely not be pleased.

Sure, there are many ways to "skin a cat," but if someone wants help with THIS way, telling him about THAT way doesn't help.

RE