From: Eric Smith on
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(a)> 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.
From: Eric Smith on
John Selck <selck_j(a)> writes:
> Same opcodes but faster clockspeed. Also, CBM switched from NMOS to HMOS.

HMOS is just NMOS with smaller process geometry. The NMOS to HMOS
transition was a bigger change than for instance going from 1 micron
to 0.8 micron CMOS, but not nearly as big a change as switching from
PMOS to NMOS, or from NMOS/HMOS to CMOS.
From: Eric Smith on
buchty(a) (Rainer Buchty) writes:
> There are quite some "it wouldn't work otherwise" examples, though,
> which require those undocumented opcodes to meet strict timing.

Such as?
From: John Selck on
Am 19.05.2006, 08:48 Uhr, schrieb Pasi Ojala

> On 2006-05-18, John Selck <gpjiweg(a)> wrote:
> 0$: stx $fe00
> sbc $10
> bcs 1$
> adc $11
> inc 0$+1
> $1:
>> Best case: 19 vs 11 clock cycles (1.73x speed)
>> Worst case: 23 vs 15 clock cycles (1.53x speed)
> Best case: 10 vs 11 clock cycles (0.9x speed)
> Worst case: 18 (17 if zeropage) vs 15 cycles (1.2x or 1.13x speed)
>> Fact remains: illegals can make a difference on certain tasks.
> In best-case your routine is slower than without illegals,
> and in average it is about the same speed.

Yes true your routine is faster, but it does not do any Bresenham
From: John Selck on
Am 19.05.2006, 06:28 Uhr, schrieb mdj <mdj.mdj(a)>:

> Of course, the point remains though that your would never do this on
> the Apple II series, as you'd limit your target market to the earliest
> machine, rather than just the lowest common denominator of all machines
> (64k, 6502 code that's documented and unbuggy)

It's easy to do a processor check.
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