25 Sep
1997
25 Sep
'97
12:07 p.m.
On Thu, 25 Sep 1997, Allison J Parent 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.
Phil
**************************************************************
Phil Beesley -- Computer Officer -- Distributed Systems Suppport
University of Leicester
Tel (0)116 252-2231
E-Mail pb14(a)le.ac.uk
Also information on the 65SC02 would be of
interest. I know it's basically
6502 but I've been told the later versions have extensions to the basic
instruction set.
25 Sep
25 Sep
1:09 p.m.
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(a)siconic.com
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