Editing MOS Technology 6502 (section)

===Introducing the 6501 and 6502===
[[File:MOS 6501 6502 Ad Sept 1975.jpg|thumb|Introductory advertisement for the MOS Technology MCS6501 and MCS6502 microprocessors]]

MOS would introduce two microprocessors based on the same underlying design: the 6501 would plug into the same socket as the Motorola 6800, while the 6502 re-arranged the pinout to support an on-chip clock oscillator. Both would work with other support chips designed for the 6800. They would not run 6800 software because they had a different instruction set, different registers, and mostly different addressing modes.<ref name="Mensch interview" /> Rod Orgill was responsible for the 6501 design; he had assisted John Buchanan at Motorola on the 6800. Bill Mensch did the 6502; he was the designer of the 6820 PIA at Motorola. Harry Bawcom, Mike Janes and Sydney-Anne Holt helped with the layout.

MOS Technology's microprocessor introduction was different from the traditional months-long product launch. The first run of a new integrated circuit is normally used for internal testing and shared with select customers as [[engineering sample]]s. These chips often have minor design defects that will be corrected before production begins. Chuck Peddle's goal was to sell the first run 6501 and 6502 chips to the attendees at the [[Western Electronics Show and Convention|WESCON]] trade show in San Francisco beginning on September 16, 1975. Peddle was a very effective spokesman and the MOS Technology microprocessors were extensively covered in the trade press. One of the earliest was a full-page story on the MCS6501 and MCS6502 microprocessors in the July 24, 1975 issue of ''Electronics'' magazine.<ref name="Electronics July 24, 1975">{{Cite journal |title=Microprocessor line offers 4, 8, 16 bits |journal=Electronics |volume=48 |issue=15 |page=118 |publisher=McGraw-Hill |location=New York |date=July 24, 1975}} The article covers the 6501 and 6502 plus the 28-pin versions that would only address 4K of memory. It also covered future devices such as "a design that Peddle calls a pseudo 16".</ref> Stories also ran in ''[[EE Times]]'' (August 24, 1975),<ref name="6502 EE Times 1975">{{Cite journal |last=Sugarman |first=Robert |title=Does the Country Need A Good {{US$|long=no|20}} Microprocessor? |journal=EE Times |page=25 |publisher=CMP Publications |location=Manhasset, New York |date=25 August 1975 |url=http://www.commodore.ca/gallery/magazines/misc/mos_605x_team_eetimes_august_1975.pdf |access-date=5 February 2008 |archive-url=https://web.archive.org/web/20070203105724/http://www.commodore.ca/gallery/magazines/misc/mos_605x_team_eetimes_august_1975.pdf |archive-date=3 February 2007 |url-status=dead}}</ref> ''EDN'' (September 20, 1975), ''Electronic News'' (November 3, 1975), ''Byte'' (November 1975)<ref name="Byte Nov 1975 6502">{{Cite journal |last=Fylstra |first=Daniel |author-link=Dan Fylstra |title=Son of Motorola (or the {{US$|long=no|20}} CPU Chip) |journal=Byte |volume=1 |issue=3 |pages=56–62 |publisher=Green Publishing |location=Peterborough, NH |date=November 1975}} Comparison of the 6502 and the 6800 microprocessors. Author visited MOS Technology in August 1975.</ref> and ''Microcomputer Digest'' (November 1975).<ref name="3rd Gen Micro">{{cite journal |title=3rd Generation Microprocessor |journal=Microcomputer Digest |volume=2 |issue=2 |pages=1–3 |publisher=[[Microcomputer Associates, Incorporated|Microcomputer Associates]] |location=Cupertino, CA |date=August 1975 |url=http://www.bitsavers.org/pdf/microcomputerAssociates/Microcomputer_Digest_v02n02_Aug75.pdf |access-date=2009-11-27 |archive-date=2009-07-04 |archive-url=https://web.archive.org/web/20090704150052/http://www.bitsavers.org/pdf/microcomputerAssociates/Microcomputer_Digest_v02n02_Aug75.pdf |url-status=dead}}</ref> Advertisements for the 6501 appeared in several publications the first week of August 1975. The 6501 would be for sale at WESCON for {{US$|long=no|20}} each.<ref name="Electronics Aug 7 1975">{{Cite journal |title=MOS 6501 Microprocessor beats 'em all |journal=Electronics |volume=48 |issue=16 |pages=60–61 |publisher=McGraw-Hill |location=New York |date=August 7, 1975}}</ref> In September 1975, the advertisements included both the 6501 and the 6502 microprocessors. The 6502 would cost only {{US$|long=no|25}} ({{Inflation|US|25|1975|fmt=eq|r=0}}).<ref name="6502 Computer Sep 1975">{{Cite journal |title=MOS 6502 the second of a low cost high performance microprocessor family |journal=Computer |volume=8 |issue=9 |pages=38–39 |publisher=IEEE Computer Society |date=September 1975 |url=http://commons.wikimedia.org/wiki/File:MOS_6501_6502_Ad_Sept_1975.jpg |doi=10.1109/C-M.1975.219074 |access-date=2012-06-04 |archive-date=2021-02-24 |archive-url=https://web.archive.org/web/20210224154043/https://commons.wikimedia.org/wiki/File:MOS_6501_6502_Ad_Sept_1975.jpg |url-status=live|url-access=subscription }}</ref>

When MOS Technology arrived at Wescon, they found that exhibitors were not permitted to sell anything on the show floor. They rented the MacArthur Suite at the [[Westin St. Francis|St. Francis Hotel]] and directed customers there to purchase the processors. At the suite, the processors were stored in large jars to imply that the chips were in production and readily available. The customers did not know the bottom half of each jar contained non-functional chips.<ref>Bagnall (2010), pp. 33–35.</ref> The chips were {{US$|long=no|20}} and {{US$|long=no|25}} while the documentation package was an additional {{US$|long=no|10}}. Users were encouraged to make [[photocopies]] of the documents, an inexpensive way for MOS Technology to distribute product information. The preliminary data sheets listed just 55 instructions and excluded the Rotate Right (ROR) instruction, which was not supported on these early chips. The reviews in ''Byte'' and ''EDN'' noted the lack of the ROR instruction. The next revision of the layout fixed this problem and the May 1976 datasheet listed 56 instructions. Peddle wanted every interested engineer and hobbyist to have access to the chips and documentation, whereas other semiconductor companies only wanted to deal with "serious" customers. For example, [[Signetics]] was introducing the [[Signetics 2650|2650]] microprocessor and its advertisements asked readers to write for information on their company letterhead.<ref name="Signetics 2650 Oct 1975">{{Cite journal |last=Signetics |title=Easiest-to-use microprocessor |journal=Electronics |volume=48 |issue=22 |pages=114–115 |publisher=McGraw-Hill |date=October 30, 1975 |url=https://commons.wikimedia.org/wiki/File:Signetics_2650_microprocessor_October_1975.jpg |access-date=November 20, 2015 |archive-date=November 20, 2015 |archive-url=https://web.archive.org/web/20151120204902/https://commons.wikimedia.org/wiki/File:Signetics_2650_microprocessor_October_1975.jpg |url-status=live}}</ref><!--[[User:Kvng/RTH]]-->