Re: Recreate 6502 Bug II

[Don Bruder <dakidd@sonic.net>]

In article <3efafc8e_1@news.iprimus.com.au>,
 "Mark Cummings" <NOTfigjams@primus.com.au> wrote:

> on a slightly similar topic I do recall that there are also Opcodes on the
> 6502 that are not all used and using them can produce different
> "undocumented" results, and this will vary for each brand of 6502. would you
> call that a bug too if a programmer used them ?

Personally, I wouldn't call it a "bug"...

I think the term I'd use would be "insanity". :) One never knew for 
sure, from brand to brand (and occasionally from chip to chip) exactly 
what was going to happen if you pitched one of those "unimplemented" 
opcodes into the instruction stream. Some of them behaved like "slow" 
(an extra 1, 2, even 4, machine cycles to execute instad of the standard 
cycle count) NOPs, other did things to the condition register or stack 
pointer (but rarely ever predictably) and others would turn the machine 
catatonic. 

Trying to use those "not-really-there" opcodes (and get predictable 
results) was a great recipe for madness...

-- 
Don Bruder -  dakidd@sonic.net <--- Preferred Email - unmunged, SpamAssassinated
Hate SPAM? See <http://www.spamassassin.org> for some seriously great info.
I will choose a path that's clear: I will choose Free Will! - N. Peart
Fly trap info pages: <http://www.sonic.net/~dakidd/Horses/FlyTrap/index.html>