7 Oct
1998
7 Oct
'98
5:01 p.m.
On Wed, 7 Oct 1998, D. Peschel wrote:
If you look at what bits are on in the opcode you can see how certain
"illegal" instructions that perform, say accumulator operations and X
register operations fit into both respective instruction families.
I bet it would
work, or at least do something of interest. The "illegal
opcodes" of the NMOS and HMOS 6502s are quite functional -- Commodore programs
are littered with suspicious opcodes like LAX (load .AR and .X simultaneously).
With all that hidden functionality, why bother with the CMOS versions? ;-)
I've always wondered about the internal construction of the 6502. Sure, you
can look at a list of illegal instructions but the list doesn't tell you why
the instructions do what they do, only what they do. And did Chuck Peddle ever show up at the VCF? He
would be THE person to ask
(OK, maybe Steve Wozniak would know too).
Nope. Didn't see him. But he'll most likely be a speaker at VCF 3.0.
Sam Alternate e-mail: dastar(a)siconic.com
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