Same issues with e.g. the Rockwell R6500 single-chip microcomputer family -- the actual microcontrollers, not their second-source MOS 6500 family chips. Rockwel

Same issues with e.g. the Rockwell R6500 single-chip microcomputer family -- the actual microcontrollers, not their second-source MOS 6500 family chips. Rockwell put I/O stuff and stack both in zero page to make more efficient use of limited ROM space, and allow operation with only the tiny amount of on-chip RAM! A lot of stuff can be restructured to live with it, but almost nothing "just works."