Hi all,

I'm finishing up the editing for Roger Wagner's "Assembly Lines: The Complete Book." I'm up to chapter 33, which comes from Softalk, June 1983. In that article, Roger is discussing the new instructions available on the 65C02 chip.

The article talks about the new "indexed absolute indirect" addressing modes. For example, JMP ($1234,X), which does "pre-indexing" by adding X to $1234, then dereferencing that pointer to find the actual jump address. That's all fine, but then the article states that this addressing mode is now available on ADC, AND, CMP, EOR, LDA, ORA, SBC, and STA.

I think that this is just a mistake, because all of the information that I can find states that for the 65C02, JMP is the only instruction that can use this new addressing mode.

My questions are - just to be sure, is this indeed true that JMP ($1234,X) is the only case for this mode? And, is it possible that there was a "prototype" or some "early-release" documentation that suggested that the new mode would be available for the other instructions? I don't want to hack out that part of the article, only to find out that I was completely wrong...

Thanks in advance for the help!

-Chris
p.s. I've attached a PDF of the article

Yes, JMP is the only one. The 65CE02 and 65816 adds JSR(abs,X).


I doubt it, but your line here is why I checked the 'CE02 which did make it into production but not very many were made.

_________________
http://WilsonMinesCo.com/ lots of 6502 resources
The "second front page" is http://wilsonminesco.com/links.html .
What's an additional VIA among friends, anyhow?

In addition to the alleged ADC ($1234,X) nonsense, the third paragraph of the .pdf article states:

I have no problem accepting the second half of the sentence (in Summer of '83 context), but the first half of the sentence seems completely contrary to the histories that I've read. I was in third grade when it was introduced, but knew nothing about it until I saw an Apple II plotting some "high-res" graphics at a science fair several years later, so I have to rely on the histories provided by others, and this particular one seems a bit shaky.

Mike

Thanks Garth and Mike. I think I'll just assume that it was a mis-reading of the JMP addressing mode, and I'll just correct the article.

Regarding the "design" of the 65C02, Roger is partially correct. According to the information that I've been able to find, the 6502 was originally designed by MOS Technology (after the engineers split from Motorola). But then, MOS Technology was indeed bought by Commodore in 1976. It sounds kind of sad - the engineers left Motorola because they weren't allowed to develop a low-cost chip. Then, after Commodore bought MOS, the R&D budget was again cut, and they ended up having to leave again. One wonders what might have happened if Commodore had developed the 65C02 under their company...

Anyway, in my edited version of the article, I've made some slight corrections to the history, to include mention of MOS.

Thanks again for the feedback!

-Chris

As Garth noted, only JMP has an indexed absolute indirect addressing mode. The other instructions do have a zero page indirect mode, e.g., LDA ($12), with the 65C02. Of course, LDA ($12,X) exists as it did in the NMOS 65xx family.

I'm sure you are aware that there are variances between different manufacturers' 65C02s. The definitive version is the W65C02S, which is current production.


That pretty much describes how it went. Jack Tramiel was a notorious tightwad who was allergic to spending money on product improvements. Although his business model pushed Commodore into the $1 billion sales range with the C-64, he created a corporate mentality that didn't want to stay ahead of the curve. By the time Irving Gould comprehended what was happening to Commodore and gave Tramiel the boot, the seeds for the company's failure had already been planted.

As for the 65C02, that was Bill Mensch's baby. He designed it from the ground up and got Apple to use it in both the ][e and ][c. History then repeated itself when the Apple ][gs went into production with the Mensch-designed 65C816. Like the 65C02, the '816 was second-sourced, but again, only the W65C816S remains in production.

Incidentally, there are other historical errors. For example:

As sometimes happens with these things, though, some of the key persons involved with the 6502 went to work at a new company, Western Design Center. This company, then, is the original source of the new 65C02 chip. But the story doesn’t end there. Western Design Center has sold the design to at least three independent manufacturers, Rockwell International, GTE, and NCR. These companies took the initial 65C02 design, corrected initial design errors, and added their own enhancements.

In reality:

1. The "key person" who left MOS Technology and "went to work...at...Western Design Center" was Bill Mensch, Jr., the founder of Western Design Center.
   
   
2. WDC didn't "sell" the design, they licensed it. There's a big difference between selling and licensing.
   
   
3. Rockwell, GTE and NCR didn't fix any design errors. As for whether their changes were "enhancements," that is a matter of debate.

Some of the instructions that the original author indirectly attributes to Rockwell were part of the Mensch design before Rockwell got involved.

_________________
x86?  We ain't got no x86.  We don't NEED no stinking x86!

That of course is false. The release of the 6502 predated Commodore's involvement with and eventual purchase of MOS Technology.

_________________
x86?  We ain't got no x86.  We don't NEED no stinking x86!

Thanks BigDumbDinosaur (?). I've added your corrections to the chapter, including the wording change from "sell" to "license". Good catch!
-Chris

A significant difference between the genuine WDC 65C02 (W65C02S) and the product shipped by Rockwell et al is the inclusion of two machine instructions in the former that along with conversion to a static core, made the WDC part suitable for use in implanted medical devices. There are also some electrical differences that make the WDC part more adaptable to a variety of applications. As well, the WDC part is capable of running at far higher speeds. Anyone who is interested in scratch-building a 65C02 device should resist the temptation to use a non-WDC MPU.

_________________
x86?  We ain't got no x86.  We don't NEED no stinking x86!

Indeed. It almost seems the word apparently is a tacet admission by the author that the matter hasn't been researched. OTOH the book is about assembly language, not history. And it's a draft we're seeing -- that's why it's still being edited!


I think we've been over this already. You're very zealous in your endorsement of WDC MPUs, BDD! Certainly they're fine products -- but not the best choice for everyone, as you seem to agree early in this thread (excerpts below).


cheers
Jeff

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In 1988 my 65C02 got six new registers and 44 new full-speed instructions!
https://laughtonelectronics.com/Arcana/ ... mmary.html

That's because I own stock in the company! Just kidding.

It's not a case of being zealous, but rather one of encouraging the use of the "definitive" version of the 65C02, since that is the only one that is in production. My comment about resisting the temptation to use the non-WDC parts, which are all NOS or pulls of sometimes-dubious origin, doesn't say one should not use them.

To be sure, the very rapid switching speeds of the genuine 65C02 can give the unwary experimenter trouble. However, the same can be said for the WDC peripheral silicon, whose MPU interface (data bus, chip selects, etc.) has to be at least as fast as the MPU itself if operation is to be achieved at the rated clock speeds. That in itself shouldn't stop one from using WDC parts, unless trying to build a circuit on breadboard with long, curvy wires. In fact, getting a computer running with WDC parts should be viewed as a design challenge and learning experience.

_________________
x86?  We ain't got no x86.  We don't NEED no stinking x86!

Hi BDD
I think you may be indeed be a little over-zealous here. Let's at least mention Chuck Peddle as well as Bill Mensch. And perhaps we can agree that WDC's 65C02 is the surviving 6502 variant - I wouldn't go so far as to call it definitive, as it was neither the first 6502 variant or the first CMOS variant. History may be written by the winners, but we needn't give all the glory to Bill. He's built a successful business but was not the prime mover.

Cheers
Ed

Mensch designed the 65C02, so that would make his creation definitive for the CMOS line.

_________________
x86?  We ain't got no x86.  We don't NEED no stinking x86!

http://en.wikipedia.org/wiki/MOS_Technology_6502



http://en.wikipedia.org/wiki/MOS_Technology

I got my first computer in 1983 which was a Commodore 64 so I only know of the MOS Technology era and I wish I knew more of the Motorola era which would answer a lot of questions about these chips. The lack of knowledge may mean that Motorola has a lot more understanding of these chips than I know.

History is often told by its survivors so that is why the Wikipedia pages are so important but the fact is that I only know of one producer left for the 6502 line.

I don't know of any other computer company other than MOS Technology that started so many computer companies:



http://en.wikipedia.org/wiki/Chuck_Peddle



http://en.wikipedia.org/wiki/MOS_Technology_6502

So yes, Motorola basically invented it but no one popularized it and started so many computer companies than Chuck Peddle and it was the outsourcing by Rockwell, Synertek, etc that got it into other devices.

Western Design Center got it into other computers / devices.

The importance today is, "What are you doing with it now?" Unless it is being used, it is almost useless.

_________________
http://WilsonMinesCo.com/ lots of 6502 resources
The "second front page" is http://wilsonminesco.com/links.html .
What's an additional VIA among friends, anyhow?

(Just to note that BDD has been an active editor on Wikipedia, which is of course a splendid thing, but it does mean that BDD and Wikipedia are slightly more likely to be in agreement!)