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Re: 6502 illegal opcodes questions

Am 18.05.2006, 10:22 Uhr, schrieb Michael J. Mahon <mjmahon@aol.com>:


I admit that I don't have a quantitative estimate of the number of
transistors (PLA terms) required to protect at least most of the
unused opcode space, but I suspect it would not be more than a few
hundred (out of about 3700 in the 6502).


And you think people would waste a few hundred just for that? Also,
you have propably noticed the lack of space on the cpu... If they
had space for a few hundred more transistors, they would rather have
added another adressing mode or opcodes like PLX/PHX or TXY etc, but
not NOP'ing out the illegals.

Btw, also x86 CPUs have undocumented opcodes aswell... and programs
do use them.