From: Tibor Biczo (crown_at_axelero.hu)
Date: 2004-07-03 17:23:42
Hi,
> Gideon Zweijtzer, who is developing the 32-bits 6502, the 65GZ032, started
> with coding a 6502 in VHDL first. He focussed only on the legal
> instructions. Then he found out that his VHDL-6502 cooud execute almost
all
> known illegal opcodes as well. This supported the idea that all known
> illegal codes are just a by-product of the legal ones. But we don't know
how
> the original engineers exactly implemented the instructions, so wanting to
> have all illegal codes simply means extra work for us mortals.
If you want to know how exactly they implemented them, than check out the
reverse engineered 6502 schematics on this site:
http://impulzus.bme.hu/6502/
As the site is completely in Hungarian I'll point out the interesting parts:
Download section:
http://impulzus.bme.hu/6502/letolt.php3
Full 6502 Die shot (20Mb)
http://impulzus.bme.hu/6502/download/6502_full.png
Schematics A3 Postscript (6.4Mb)
http://impulzus.bme.hu/6502/download/6502_A3.ps
Schematics A4 Postscript (10.4 Mb)
http://impulzus.bme.hu/6502/download/6502_A3.ps
Tibor
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