Re: 6502 illegal opcodes questions

[heuser.marcus@freenet.de]

> So it seems the message is, "If you have good reason to believe that
> you are programming for an 'end of the line' platform, then do anything
> that works--it won't matter anyway".

In my opinion this approach is too fatalistic - after all Commodore and
Atari didn't really offer CPU-upgrades. The C128 is more or less
completely compatible (illegal opcodes supported) and Atari didn't
offer anything faster or based on a more modern chip.

Therefore their programmers (third party or hobbyists) never really had
to worry about doing something "illegal" when using these opcodes.

Apple on the other hand introduced the IIc quite early in comparison.
It's success and the subsequent enhancement kit for the IIe /
modernized IIe effectively killed the usage of these opcodes in the
Apple world. Side note: I would love to hear from Apple why they chose
the 65C02 - because of the much less power using CMOS design or the
additional features...

And then of course came the 68K-platforms and took over the market...

> In the case of a video game machine, I wouldn't expect any compatible
> upgrade path, and the entire hardware arrangement was very ideosyncratic
> anyway--so there would be no reason not to do "anything that worked".

Good points.

What would be interesting to know is when did the 6502 programmers
begin using illegal/undocumented opcodes. Right from the start? I
vaguely remember hearing about them first in the mid-eighties.

bye
Marcus