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Re: 6502 illegal opcodes questions
Eric Smith wrote:
"Michael J. Mahon" <mjmahon@aol.com> writes:
The 6502 was already a much less expensive processor than its
competitors, because of a mask retouching technique MOS Technology
developed that saved mask iterations.
I saw that claim on Wikipedia. Is there any published reference?
Although the target was dead, the Google cached page at:
http://66.102.7.104/search?q=cache:uNXP83T5hq0J:www.commodore.ca/history/company/mos/mos_technology.htm+6502+die+photo&hl=en&gl=us&ct=clnk&cd=5
(sorry about the length) is "The Rise of MOS Technology & The 6502"
Written by Ian Matthews of commodore.ca February 15, 2003, Seriously
revised and expanded on January 18, 2006.
The relevant excerpt follows:
>>>
In the 1970's, 70% of the industries chip production were defective and
therefore garbage. This substantially increases the cost of each viable
chip. When a chip is being laid out for etching on a silicon wafer, it
drawn at a large scale and then photo reduced over an over again (just
like a photocopy reduction) until its microscopic size will fit on the
required die. Each reduction layer is called a Mask. MOS figured out a
process to repair Masks as they are reduced. The end result was that
they had a 70% success rate. This obviously reduced the per chip cost of
manufacturing and made the $25 processor a possibility.
<<<
Frankly, this article (like virtually all technology articles) has
enough casual inaccuracies (like spelling Mensch's name Mench), that
I can't be sure that this is an accurate rendition of the truth.
But is is a plausible story, since repairing a mask master later
than the rubylith stage is a time and cost win.
-michael
Music synthesis for 8-bit Apple II's!
Home page: http://members.aol.com/MJMahon/
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