On the one hand, the Z80 was indeed a CPU you could easily wrap your mind around, on the other hand, similar sheets exist for Intel chips (from the same author: https://vtda.org/docs/computing/MicroLogic/MicroLogic8086&80...), so maybe the differences between architectures aren't as stark as we like to think?

Having said that, I'm not sure how actually-useful this particular reference card is: huge hex conversion table, but no instruction timing chart?

Anyway... pure nostalgia caused me to go through an old Z80 assembly book just now ("Advanced Spectrum Machine Language"), and I found some code I wrote a good 35 years or so ago: https://ibb.co/fvqtwkQ

This was printed on thermal paper (not sure about the printer model: I don't think it was the original ZX Printer, as that used differently-sized paper), so sort-of impressed it survived that long (most printouts I had from that time long faded). As to why I wrote the code or what it does: I think it was to create an animated tape loading screen, but...