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 "Design Philosophy Behind Motorola's MC68000" 
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Joined: Wed Jan 09, 2013 6:54 pm
Posts: 1789
From BYTE magazine, 1983, a series by Thomas Starnes of Motorola, all about the 68000, collected into one PDF.
Design Philosophy Behind Motorola's MC68000

    Part 1: A 16-bit processor with multiple 32-bit registers
    Part 2: Data-movement, arithmetic, and logic instructions
    Part 3: Advanced instructions

Sun Sep 13, 2020 1:49 pm
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Joined: Mon Feb 03, 2020 4:08 am
Posts: 6
Location: Planet Earth, FL, USA
Nice find.... I went into my Byte collection.... the articles are in April, May and June. Obviously, I forgot about the 68000 articles... but have a fairly large collection of Byte magazines dating back to 1982. I'm sure there are more 68000 related articles, I should probably go through the collection and find the rest. Thanks for posting this!

Regards, KM

Sat Sep 19, 2020 2:56 am
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Joined: Wed Oct 23, 2019 8:07 pm
Posts: 2
Thanks for posting these articles on my favorite micro. My first real (paying) design was a 68010 SBC. I love this bit:

"The MC68000 is generally considered a 16-bit microprocessor, though it uses 32-bit addresses and contains 32-bit registers. It also can operate on 32 bits of data as easily as 8 and 16. Many users of the MC68000 consider it a 32-bit just as much as a 16-bit processor."

Size-matters debates like this will probably go on forever. The "right" answer is, the 68K is 32-bit. The register size is the dominant characteristic, not the number of wires in and out of the package.

Sat Sep 19, 2020 12:13 pm

Joined: Wed Jan 09, 2013 6:54 pm
Posts: 1789
Hee hee - welcome picosecond! I think debating the width of a processor is rarely enlightening, or satisfying. Although, in rare cases where the databus, address bus, register file, ALU, and instructions are all the same fixed size, there is at least an answer.

There's a nice pair of articles about the genesis of the 6809 somewhere... ah here they are, 3 in fact, again in a single PDF.
A Microprocessor for the Revolution: The 6809, by Terry Ritter and Joel Boney, in BYTE, Jan 1979.
Part 1: Design Philosophy
Part 2: Instruction Set Dead Ends, Old Trails and Apologies
Part 3: Final Thoughts

Sat Sep 19, 2020 1:08 pm

Joined: Wed Jan 09, 2013 6:54 pm
Posts: 1789
Oh, see also this earlier thread, for articles on the 8086 and 9900.

Sat Sep 19, 2020 1:11 pm
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Joined: Wed Oct 23, 2019 8:07 pm
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Thanks for the articles, BigEd. It is interesting how familiar the VLSI design challenges from 40+ years ago are today. The more things change, the more they stay the same.

In case the snark wasn't evident, I am in complete agreement about the pointlessness of processor width debates.

I wonder if the 6809 was a good investment. The world might be different today if Motorola had put those resources toward the 68K.

Sun Sep 20, 2020 1:12 pm

Joined: Wed Jan 09, 2013 6:54 pm
Posts: 1789
There's an oral history panel where the 6800 team are quite happy about the huge volumes they shipped into automotive applications - we (I) tend to forget how many cars there are, relative to how many computers, especially back in the day.

Eventually, I'm sure, cars got their share of 68000 or 88000 or POWER chips to run them. I don't know if 6809 got into automotive in a big way.

But it's a fair question: how much business did the 6809 get. I think I recall that the 68000 was a very long time coming - maybe a stopgap was just the thing. Like the 8086!

Sun Sep 20, 2020 1:31 pm
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