On 6/13/2022 at 7:35 PM, codewar65 said:
The 65816 was an abomination IMHO. If it had full dedicated address pins, I might say otherwise. lol
Behind many design elements considered to be "abominations" by some often lurks that horrible phrase, "commercial considerations". AFAIU, Apple LIKED the smaller CPU footprint that resulted from multiplexing D0-D7 with A16-A23. Nintendo certainly did, and the design license fees flowing from the SNES was a much bigger cash cow than any 21st century hobbyist systems are ever going to be.
If used for a 64K address space for a 65xx family system, with RAM and I/O conditioned on PHI2 high, it seems to me that the high address space can simply be ignored.