thanks a lot for explanations!
A bit more wonder though. 6800 and 8080 themselves are microcontroller, would it be better if they could support both (or more) controlling scheme? Is it right that which controlling signals are used, RD/WR or EN, are more about the choice of external memory devices, and microcontrollers should support all, to make themselves able to work with several type of external devices? Or that's just the way it was in the ancient time of 6800 and 8080 when microcontrollers support only one controlling style?