From my last question, I now understand how to use one Z80 PIO chip.
I'm having trouble understanding how I would wire multiple PIOs up, though. The more I think about it, the less sense it makes.
I mean, I can think of a few ways to do this:
- Use a demultiplexer with, say, the last 3 bits of the address bus as inputs, and then connect each output to the enable pin of a different PIO chip. The issue I see here is, how do I then use the A/B and C/D pins on the PIOs?
- Use the first two bits of the address bus for A/B and C/D pins, and use the rest to indivually select each PIO chip. The issue here is that unless I'm careful whilst addressing the ports, I could enable two PIOs at the same time.
So, none of these two ways seem to be the "right" way to do it. Is there a standard way of achieving multiple PIOs being controlled by the Z80?
Best Answer
I've never built a Z80 computer (or any other) but have had to explain basic micro-computer operation to maintenance personnel and I found this schematic very useful. With a little study you should be able to find a variety of clever techniques and tricks the designer used to get the most out of the limited number of address lines available.
The linked article and schematic are worth a read.
Again, I have no expertise in this area but I imagine that every trick possible was used to get the best out of these devices.