Re: 6502 illegal opcodes questions

[Eric Smith <eric@brouhaha.com>]

Michael J. Mahon wrote:
> The fact that both companies used "custom" 6502 processors for their
> machines is no doubt part of the reason that they never moved forward.

John Selck <selck_j@informatik.hgv-hamburg.de> writes:
> Huh? They did move forward. 6510 -> 8500 -> 8502.

That was a progression of nearly insignificant changes.  Not comparable
to e.g. the 8086/80286/80386 progression, or even to the
6502/65C02/65816 progression.

> And also, I don't
> think it's any kind of problem for Commodore to use customized CPUs
> since they owned MOS, the owners and producers of 6502 tech back then

Yes, it was a problem for them.  Designing (or even just modifying)
a processor costs a lot of money, even if you own the fab.  You don't
do it unless you have a business plan with a reasonable expectation
of (more than) recouping those costs.

In a modern process, a production mask set costs about $0.5-$1 million
if you don't own the fab, maybe 20% of that if you do.  Back in the
1980s with larger process geometries the costs were lower, but still
not insignificant.