Talk:MOS Technology 6502

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Photo of 6800 board

Hi. Why is there a photo of a 6800 demonstration board? Although some of the same engineers designed both, I don't think it's relevant and it should be removed. - Richard Cavell (talk) 17:18, 12 January 2017 (UTC)

You mean the “Motorola 6800 demonstration board built by Chuck Peddle” in the “Origins at Motorola” section. This shows that Chuck Peddle was very familiar with the 6800 processor while he worked at Motorola. There was a bit of a dust up about Chuck copying the 6800 design. The board is notable and is on display at the Computer History Museum in Mountain View, California. -- SWTPC6800 (talk) 22:56, 13 January 2017 (UTC)

Fine, but why is it in the MOS (not Motorola) 6502 (not 6800) article? The same engineer designed the Pontiac GTO and the Chevy Vega, but the Vega article doesn't have a picture of the GTO. Jeh (talk) 23:12, 13 January 2017 (UTC)

The GTO engineers did not take General Motors documents to a new company to design a lookalike car. Chuck Paddle actually built this prototype board. It shows the background experience in microprocessors of one on the 6502 designers. -- SWTPC6800 (talk) 03:17, 14 January 2017 (UTC)

I don't think that's sufficient reason. Articles should be about their subjects. The subject here is the 6502, not the 6800. Chuck Peddle is a subtopic within this article it but this demo board shows his work on a different project for another company. Per the 6800 article, he didn't design the 6800 architecture; his role in the 6502 project was different. Nobody is saying the board isn't notable or isn't worth a picture, only that its picture doesn't really add to the presentation of facts in this article. I agree that the demo board has some relationship to the 6502, but that relationship is too tenuous to support the picture being here. Why isn't there a picture of an early demo board for the 6502? Or maybe of the justly famous KIM-1? Conversely, why isn't this picture in the 6800 article? Jeh (talk) 02:08, 17 January 2017 (UTC)

The Apple I has jumpers to select 6502 or 6800, the pinouts are very close. I suspect other boards were designed to work for either chip. Gah4 (talk) 20:57, 1 March 2018 (UTC)

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How many have been produced so far?

According to minute 3:00 of this talk on YouTube, more than 10 billion were produced by one company alone. It would be nice to have a proper source for production numbers (presumably of the entire 65xx family) so the information can be included in the article.

Name of stack pointer

"SP" is common usage for other machines, but the hardware data sheet agrees with the text, which refers to it as "S". TEDickey (talk) 02:11, 8 November 2019 (UTC)

OK although my extremely dim recollection is that "SP" was common. At any rate, whoever created the table certainly thought "SP" was right because they helpfully bolded the full name (Stack Pointer) in the same manner done for PC. It is true that the instruction set includes TXS which uses S and PHA is defined in terms of S. Johnuniq (talk) 04:13, 8 November 2019 (UTC)

The designers needed registers to have single-letter name if they're to be used in the instruction mnemonics that they'd fixed at three letters. PC isn't so they could go with convention. SP is so that may be why it's only S. My opinion of the datasheet at the time was that two letter names were clearly used for two-byte registers and one letter for single byte registers. That might be led by my Z80 experience, as it used that naming scheme. But so might the 6502 designers/datasheet-authors, who would have known of the 8080 which used the same register naming scheme. I remember it described in many places as a 16-bit register with rollover in the low byte and always 01h in the high byte. Either way, we should go with what the datasheet and the instruction set use rather than anyone's recollected opinion, otherwise we're writing conjecture.ToaneeM (talk) 09:19, 9 November 2019 (UTC)

Of course, but the data sheet nowhere says "the stack pointer register is known as S". I listed what it says, and it simply uses S in a couple of places where extreme brevity was required. Johnuniq (talk) 02:31, 10 November 2019 (UTC)

Page 31 of the hardware manual lists the registers and calls it S there as well, without the need for brevity TEDickey (talk) 11:27, 10 November 2019 (UTC)

That sounds conclusive: S it is, of course.ToaneeM (talk) 16:43, 10 November 2019 (UTC)

Layout engineer for 6502

The text as written suggests that Bill Mensch did the "rubylithing" of the 6502 mask set. But this is disputed by Harry Bawcom in https://research.swtch.com/6502

"Bill Mensch did not layout the 6502, I did, with the help of two others.

In truth we all worked as a team but Bill didn't draw a single line on the first version of the 6502. My initials were on the die."

I suggest that "the layout" has two meanings here that get mixed up in a subtle manner: one meaning is the placement of functional blocks and buses (Mensch was probably responsible for that as a "design engineer", as an extension of the circuit design). The second meaning is the conversion to individual polygons: orientations, traces, as well as logical and physical design rule checks (Barcow and others would have done that as a "layout engineer"). — Preceding unsigned comment added by 95.128.95.14 (talk) 17:28, 9 January 2020 (UTC)

Primary source

A huge amount of the detail in the "History and Use" section comes from a primary source -- a YouTube video interview with Chuck Peddle. The Wiki policy on primary sources allows their use, but only sparingly; no synthesizing or interpretations based on those sources should be done, otherwise that strays into WP:OR territory. Since so much of this section relies on a single primary source, anyone who wants to work on this article should, instead of expanding it or adding more detail, try and find reliable secondary sources which can back up or correlate what was said in that interview, if possible. A lot of the detail in this section straddles the line between straightforward facts (which *can* use primary sources as citations) and analysis/interpretation of what Peddle is saying (which is *not* allowed). I don't feel the issue is so egregious as to warrant any removal of material right now, but I do think efforts on this article should be focused primarily on getting rid of the dependence on primary sources as much as possible.

I don't want to throw a bunch of tags in the article as that would make it look quite messy, so I decided to just post this here on the talk page instead. If I find time in the near future, I'll get to work on this. In the meantime I encourage anyone looking at working on this page to search carefully for quality secondary sources. MrAureliusR_Talk! 03:47, 1 December 2020 (UTC)

@MrAureliusR: I believe you are incorrectly interpreting why primary sources need to be examined carefully. The issue with primary sources is not simply who made them, but when they were made. The operational definition in this case is:

A primary source was a source that was created at about the same time as the event, regardless of the source's contents.

The concern is that someone writing about events that happened to them as they happened will not be an accurate reflection of those events or maybe deliberately obscuring them. The section on "How to classify a source" clearly spells this out.

Consider, for instance, if this was an article by Chuck when the 6502 was released and it contained statements like "Best processor ever!" In that case, one might be sceptical of its accuracy. But here we're talking about statements made decades later, surrounded by incredible historical detail, lacking any sign of obfuscation that I can see.

I do not see an attempt to examine this source critically, simply "primary bad". So do so, examine the source carefully. Do you see any reason to believe it is not an accurate account of the events, other than "primary bad"? If so, we have something to talk about. Maury Markowitz (talk) 14:21, 3 February 2021 (UTC)

The issue is that it's a YouTube video, which are discourages as sources (as far as I understand it) and also, it's just one person talking about their memory of events. There is no way to verify that what Chuck is saying is accurate. This is why secondary sources, which have researched & verified his statements, are so important. Anyone can say anything on any social media or video platform. I'm not doubting Chuck's integrity or memories; but having this entire section be based on *one person's account* of what happened over 35 years ago isn't exactly the shining definition of reliable sourcing. MrAureliusR_Talk! 19:26, 4 February 2021 (UTC)

I see nothing actionable in this post. Feel free to add more sources when you find them. Maury Markowitz (talk)

Section "Moving to NMOS" implies that the 6502's competitors were PMOS chips. Actually they were enhancement-load NMOS.

@Maury Markowitz: (Pinging Maury Markowitz because he wrote the text involved.) This whole section, describing some of the semiconductor advances in the 6502, implies that the 6502's competitors, including the Intel 8080 and Motorola 6800, were PMOS microprocessors. This is incorrect—both were NMOS chips. (Intel used PMOS for its 4004, 8008, and 4040.) The difference is that the 8080 and 6800 used enhancement-load NMOS rather than the depletion-load NMOS used in the 6502. The multiple voltages given, +12V, +5V, and -5V, are characteristic of enhancement-load NMOS rather than PMOS. Intel's PMOS chips used +5V and -10V.

I'm not doubting that MOS Technology's existing fabs were PMOS, by the way.

--Colin Douglas Howell (talk) 05:22, 3 February 2021 (UTC)

@Colin Douglas Howell: You are correct, the change was to depletion mode NMPS, which I have mentioned in the 6800 rewrites. I only came across this detail after making the edits to this article. However, I am not convinced that MOS used PMOS and hadn't already moved to non-depletion NMOS. Maury Markowitz (talk) 14:04, 3 February 2021 (UTC)