The Adventure Begins (Diving Deeper into the Z80)

[MicroNut]

I decided this weekend to jump back into my electronics hobby by making my own version of the Z80 for my FPGAs. I have found a site that already has made one by reverse engineering the Z80 die. The site highlights some logic and also has schematics of the logic.

It is my intent to use a Logic simulator called Digital to copy these schematics into it. The simulator can generate truth tables, Verilog and VHDL code. It also runs test scripts. Using the simulator I will be able to test the validity of the schematics and to better understand the logic. Once that is done I will make the FPGA softcore with what I learned.

Eventually I will make a minimal operating system on my DE10-Lite and use a serial terminal to communicate with it.

As I go through this I plan to document my findings. I remember having the book ZX81 Explorer's Guide which was a very good book and was a bit light hearted as well. I found that refreshing so I'm writing it in the same style. I even had AI generate cover art for it which I attached.

I have a Github account and will post everything as I go along with this project.

EDIT: Changed the cover art to something I liked more.

[MicroNut]

Just got my Github site up. The guide only has a forward, introduction and chapter holders as an outline. This will probably change somewhat as I go through my research.

[granz]

Just got my Github site up. The guide only has a forward, introduction and chapter holders as an outline. This will probably change somewhat as I go through my research.

I got a 404 error.

Is your page open to people who are not logged in? I had something like that happen to my son, and it turned out that he had something marked so that only people who were logged in could see it.

[MicroNut]

I had the repository set to private. I changed it to public. I then tried it without logging in and it works for me.

[granz]

I was able to get in, and read now, thanks.

It's looking pretty good, so far.

[JKnightandKARR]

I had the repository set to private. I changed it to public. I then tried it without logging in and it works for me.

I was able to get into it as well.

[granz]

Brian,

I was just looking over your book again. If you don't mind some critiques, the crumpled paper background, along with the weird font, make reading a bit of a chore. The material seems pretty good (so far I've gotten through your introduction) but it's a bit rough reading (probably mostly my old eyes.  )

The best reading, for me, is a simple Times New Roman, or Ariel, font, on a plain solid-color background. Also, be careful of the contrast - I've been running across web sites where they have a very light gray font, on a nearly the same background. That is very difficult, and I've actually had to leave some sites, in spite of very interesting material on the site.

[Chris Savage]

Question: on page 8, are the clk and oe labels reversed? It looks that way to me.

[granz]

I saw this posting in the RetroComputing forum, and thought about your book:

https://retrocomputingforum.com/t/hello-i-wrote-a-book-about-the-z80/6319

It looks like he will be selling it; maybe you could get a few bucks from your book.

[MicroNut]

I stopped mine because my intent was to explain the logic of the Z80 from another person's reverse engineering into logic blocks for use in a FPGA and when I got to the Program Logic Array that decodes opcodes he wrote it in python. The python was quite extensive and I felt it would be too time consuming to figure out the logic. I did get permission to use his reversed engineered schematics and since he made it freely available I felt it was only fair that mine was free as well.

I have decided to do more background work before moving on so I'm using a logic simulator, LogiSim-Evolution and the book Build your own computer from scratch to get more familiar with the architecture and logisim. I also found various sites building a cpu for a FPGA.

The next few months I'm going to research this then attempt a COSMAC 1802 then a Z80 in LogiSim and if successful I'll do a rewrite for building a 1802 and Z80 in LogiSim. The LogiSim-Evolution version has a fpga export function that can be customized for specific boards.