Thanks for the mention !
I've heard someone say, that the Z-80 (and 6502) are about the last fully comprehendable unit. Now things go more specialized. I obtained a lot of my Z-80 training by way of
'The Z-80 Manual's by Rodney Zak's.
Plus the usual 8-bit numbers are easy, compared with memory segmented functions, as in the 68000 IC.