Next steps in learning computer design
There are lots of abstract teaching books. Perhaps the most famous being Hennessey and Patterson's "Computer Architecture" [Patterson and Hennessey's Computer Organization and Design: The Hardware/Software Interface] and (https://www.amazon.com/dp/0123747503). The first is more for hardware design folks. The second is more for software types, who want a little hardware with their software. (The second one also comes with specialized versions for MIPS, ARM, and RISC-V.)

But those above are much more designed for a classroom setting where there are advisors, lectures, and other students to co-ordinate with, as well as exercises and lab work to do.



For a book that includes a multiplier design, you might consider Douglas Smith's "Hdl Chip Design: A Practical Guide for Designing, Synthesizing &amp; Simulating Asics &amp; Fpgas Using Vhdl or Verilog". It includes dividers, as well. And many other interesting functions.

It's an early book by a British author who moved to the US around the time of writing the book. (I spoke with him soon after his arrival in the US.) The book does something unique: It is written in "parallels" where on one side there is the function performed in Verilog and on the other side there is the same function performed in "VHDL." And the book doesn't only present one way to do things. It also elaborates on the trade-offs. Finally, this book is definitely designed for the absolute beginner. So it's pretty easy to read.



Ben Eater has a bunch of web pages and videos to help you actually build something using 7400 series parts (and a few other electronic parts, of course) that will handle 8-bit data and instructions. You might look up those. They are somewhat scattered, in a way. But they aren't terribly hard to understand and, I think, people here would be helpful with specific questions as you proceeded through them. So this might be one approach to take a look at and see if it fits your interests well enough.



There is Logisim (which is, now, a long-retired software product) that performs logic simulations and includes a lot of useful "parts" you can apply. You should be able to find some completed MCUs using Logisim on the web. Having something concrete like that, which you can simulate, goes a long way towards learning.

I don't use Logisim for anything now, because there is something much better. This is Neemann's DIGITAL product. This is actively maintained and actually includes several different MCU implementations in its installation. So you don't even have to go looking around.



For a complete, step by step, design of the Z80 processor you could do no better than Monte Darlymple's "Microprocessor Design Using Verilog HDL". This is a very, very serious and very, very detailed step-by-step process that goes all the way from ground zero to a final result. It's very good.



If you are just interested in a beginner's overview (and by this I mean that the book goes into enough interesting detail without going all the way to completion), then I think perhaps the easiest book of all to read on the topic is Clive Maxfield's "Bebop Bytes Back: An Unconventional Guide to Computers".



For just fun, also have a look at Harry Porter's Relay Computer.