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Have a look at this book https://cc-webshop.com/collections/books-electronics/products/microprocessor-design-using-verilog-hdl https://cc-webshop.com/collections/books-electronics/product... He designs a Z-80 from scratch, giving Verilog hints / good practice along the way. The design isn't 'complete' -- you have to learn what he's saying and add in the other parts. It's not a 'trivial' book but if you want to Get Good -- recommended.