retroelectro
Figure 6. MOS6501
Figure 7. MOS6502
did; it was all brand new, and mainframes with terminals seemed like the most cost-effective way forward. Once again, the team at MOS Technology did not believe in this low-cost idea, but the company’s president, John Paivinen, did. Paivinen was Peddle’s manager at General Electric’s Computer Division in the 1960s. He would have remembered Peddle’s ‘Distributed Intelligence’ concept, and he knew that the technology was there to make it possible now. Starting from scratch, with their own knowledge and unique skills, they now have an in-house IC fabricator. Peddle took the billet of ‘program manager’ and modeled the product after all of the customer interactions he had going all the way back to the JCPenney computer crash a decade earlier. All of the lessons learned from working with GE, Exxon, ITS, and Motorola all overlapped into the perfect product summary
that became MOS Technology’s magnum opus. They worked tirelessly to create a functional and affordable microprocessor that would take the market by storm. They initially devised two designs: the MOS6501 and the MOS6502.
and they can bring a lot of money online.
MOS6502
MOS Technology’s crowning achievement is the MOS6502. With a limited instruction set, it was fully capable of meeting nearly every customer’s needs, including cost. Through some real innovations in masking and die fabrication, MOS’s manufacturing yield was higher than Motorola’s and this was due to several innovations and clever design decisions.
MOS6501
Figure 8. The 6502 team from right to left: Sydney-Anne Holt, Michael Jaynes, Harry Bawcom, Chuck Peddle, Ray Hirt, Rod Orgill, Bill Mensch, and Wil Mathys. Seated: Terry Holdt.
The MOS6501 was pin-compatible with the Motorola 6800. While it used an entirely different instruction set and was not a direct replacement, if you had a design built around the 6800, you could likely replace it with a 6501 and make it work with relatively light effort. … As a final insult to Motorola, it was sold for $20. This part of the story ends with a lawsuit. Motorola sued MOS Technology over the MOS6501 and won, forcing MOS to pull it from the market. It is not known how many MOS6501s were actually sold, but estimates are below a thousand. Very few are known to exist today,
than Motorola or other companies for that matter.
placed over the wafer, coated with a light-sensitive photoresist material during the process. Ultraviolet light is then shone through the mask, transferring the pattern onto the photoresist. The exposed areas of the photoresist are chemically altered, allowing them to be selectively removed. This leaves a precise pattern on the wafer, which guides subsequent processes such as etching or doping. Making the mask is expensive and time-consuming, but each time you use it, it could collect tiny dust
particles and create new defects, becoming less and less effective. This is because if there’s an error, scratch, dust, etc., on the mask, it will be transferred to every single die it is used with. This was a real nuisance for many companies, like Intel, Fairchild, and Motorola. The team at MOS developed a unique way of fixing their masks using lasers to correct the mask from imperfections in between uses, called Mask Zapping. This dramatically increased yield to over 90%, while the competition was
Mask zapping In IC production, a mask is an essential tool in the
Die size
Since the 6502 had a limited instruction set and fewer
photolithography process. It acts as a stencil, defining the intricate patterns of the circuit that will be etched onto the wafer. The mask contains a series of opaque and transparent regions corresponding to the desired design, shining light on some areas and leaving shadows on others. The mask is
capabilities than the 6800, its die was significantly smaller allowing them to fit more on their three-inch silicon wafers. This meant that, even if they had a lower percentage yield than Motorola, they could still produce many more working units
we get technical
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