when I was little I was always fascinated with how things worked.  and back in the TRS-80 days it was simple and clear.  well things have progressed GREATLY since those days, and its a lot less understandable to the base user these days.  you add this nostalgia to my wishing to flex my school knowledge some in the decades since and I came up with this…

So I started building my device using a program called Logisim I’ve had some issues loading the site lately so heres the direct download on Sourceforge.  once I started progressing with that I realized its not even USABLE.  short of manually setting the logic/etc and watching the output and using an excel sheet manually its not what I wanted.    so naturally I took the big leap into something I knew very LITTLE about which has the power to do what I want (realize the actual CPU).

So as much as this is me building a CPU and yes I will demonstrate every piece for you as I do this in logisim, I will also keep the FPGA code base up on GIT with it so you can see and learn with me.

First off, I do NOT expect this to be overly useful to anyone for anything real as it’s an old school 8 bit CPU, and I expect about as much power as the old Z80.  It will be nice to at least say “I DID IT!”  but who knows, maybe one of you will take the base learning and turn it into something real world with some actual power.

Now for starters.  the base of the CPU is going to be the ALU (Arithmetic logic unit)  and in my design i’m going to start it with the basics.  lets ADD something.

Watch for the next post where we start the actual work.

Leave a Reply