Now why would you do THAT?

How are we going to power this thing? To start with, I have been using a bench power supply.  This is a very nice device, but not a good long-term solution. When the project is finished, I will most likely use a Jaycar MP3486 5V regulated plugpack .  These devices retail for around $A20 I don't think it's worth even designing a power supply.  We need only a single 5V rail and this supply has a 1.5A capacity which should be sufficient. If it's not enough, there is the MP3480 with a 3A rating. You might need to be a little forceful to use the latter with a breadboard however, because of the wire gauge.

Single Stepping So far, there's no reason why things should not just work.  But what if there's a problem?  Last night I was trying to work out why one of my address outputs didn't work right, and it occurred to me that since the Z80 is essentially a static processor, it would be pretty easy to add a single-step clock to our design so far. All this requires is a 74LS00 a Single-Pole Double-Throw (SPST) pushbutton switch and a couple of resistors.  Now, for each push of the switch we get one clock transition.  I will update the main schematic soon to reflect this change, and provide a way of selecting either option without rewiring, but since I'm working on breadboards, this is not too big a challenge to change over at the moment. Another option would be to use a very low speed clock.  We could either have a separate RC oscillator, or divide down the 8MHz signal to pretty much anything we like. What would you rather see?