🚀 go-pugleaf

On Mon, 11 Jun 2018, Quadibloc wrote:

> On Monday, June 11, 2018 at 2:20:19 AM UTC-6, Andy Leighton wrote:
>> On Mon, 11 Jun 2018 08:00:27 +0100, Ahem A Rivet's Shot <ste...@eircom.net> wrote:
>
>>> 	The Motorola engineer who came to talk to us about the 6809 and
>>> actually talked about the 68000, which had come off the company
>>> confidential list so recently that the documents still had the security
>>> legends, gave the strong impression that the 6809 was deliberate practice
>>> for the 68000 which is what they wanted to do but weren't ready for.
>
>> I am not so sure about that. The 6809 seems like an outgrowth of the
>> 6800. Take for example the registers - the 6809 just had A and B (like
>> the 6800) but could also treat them together as a 16bit register (like
>> the Z80's BC,DE,HL), whereas the 68K had 8 32bit general purpose
>> registers. That's a big difference in design philosophy.
>
> That's definitely true - the 6809 was an improved 6800.
>
> But since it did have a hardware multiply, designing it did still give some
> experience relevant to making the 68000, I would think.
>
But I thought the two were almost concurrent in design.

There was a three part article in Byte about how they came to the 6809's 
architecture, and it was by studying how the 6800 was used.  It was also 
intended to be useful by a higher level language, the two stacks hint at 
that.  They didn't take the 6800 and add things on, they studied the 6800 
and improved on it.

But given the time, the 68000 was probably in design around the same time. 
And the 68000 is not an extension of the 6909, it's a big shift to a 16bit 
processor.

It's not unlike the Apple IIGS, which has that CPU that can be shifted to 
a 16bit CPU rather than a 6502.  It came out after the Macintosh has come 
out, a different path rather than an intermediate step.

We heard about the 6809 and the 68000 about the same time, if I recall 
properly.

   Michael