On Thu, 25 Sep 1997, Phil Beesley wrote:
> There was some discussion on chip differences recently in the Apple II
> newsgroups so you may pick it up using something like DejaNews. The
> 65SC02 was apparently also used in the Franklin Ace 2200, an Apple
> IIe-ish clone, and some games allegedly did not like the fact that it
> wasn't a 65C02.
Some software took advantage of the new instructions and would not work
on an old 6502 (ProTerm v2.0 I remember in particular since I wanted to
use it but only had a lowly unenhanced //e). As well, some software
would crash on the 65C02 because they took advantage of bugs in the
6502. Once in particular was an indirect jump that crossed a page
boundary. Like so...
0800: 20
...
08FE: 6C 00 10 JMP $(1000)
...
1000: 00 40
..
2000: 00 60
Ok, so those who know what an indirect JuMP instruction is supposed to do
on a 6502 would suspect that this will jump to $4000. Well, you're
WRONG! It actually jumps to $6000. The bug was, instead of getting the
address from $08FF-$0900 like you'd suspect, it was getting it from $08FF
and $0800 instead! So instead of looking at $1000 for the address to
jump to it would look in $2000. Funky. One game I know in particular
that fell victim to this bug in its attempts to thwart pirates was
Randamn. It will crash on an enhanced //e or //c, and probably a //gs as
well. I have a fix for this if anyone cares.
Sam Alternate e-mail: dastar_at_siconic.com
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Received on Thu Sep 25 1997 - 13:09:34 BST