Michael J. Mahon wrote:
John Selck wrote:Same opcodes but faster clockspeed. Also, CBM switched from NMOS to HMOS.So this was an algorithmic rework of the original design for a new process, not a new logical design.
This is splitting hairs. Bill Mensch created the 65C816 and 65C02 designs, which are most definitely *new*, as they did not share any of the original design. However, the '02 was not a new logical design, just a redo of the existing NMOS 6502 to take advantage of CMOS.
As well, I know there are ways to create new CPU designs that preserve undocumented behavior of older designs, designs that add extensive feature sets to the original design (8->16 bit transition, etc.) Even Intel has done so (the FFFF segment wrap in the 8086) as they created news designs.
At the end of the day, enough time passed with the NMOS 6502 core in play in the CBM world that it became the norm. It was (and is) not always seen as bad programming practice in the context of CBM development to utilize the illops.
Jim