Intel VS Motorola (Was: interesting DEC Pro stuff on eBay

[Tony Duell]

On Thu, Apr 21, 2022 at 11:14 PM Fred Cisin via cctalk
<cctalk at classiccmp.org> wrote:
>
> On Thu, 21 Apr 2022, Mike Katz via cctalk wrote:
> > Intel has never understood interrupts or good cpu architecture.
> > Look at the segment:offset architecture of the 8086 and of course it's single
> > interrupt (without the separate interrupt controller chip) vs the 68000
> > somewhat orthogonal 32 bit architecture and 256 interrupts with 8 levels
> > built into the chip.
> > I could spend pages just describing how the 68K chip just blows away the 8086
> > considering they were both released at about the same time.
> > For crying out loud the 6809 even though it only addresses 64K is a more
> > powerful processor than the 8086.  Even with the 8086 clocking faster than
> > the 6809.
>
> The over-simplification that I gave my beginning students:
>
> Intel's chip design technique was to add features to the currect chip to

IMHO Intel never designed a chip that did not have bugs/misfeatures!
They must be the only company that mangled the design of a parallel
port chip -- the 8255 has the interesting 'feature' that writing to
the mode control register will clear all output lines to 0.

Think about that. After a  reset all ports are set to be inputs. That
makes sense, if they were outputs a port line could contend with
something that expects it to be an input and is trying to drive it. So
the port lines are effecrively floating. A TTL input connected to one
(which will be driven by that port line used as an output) will float
high, And of course it's a lot easier to pull a TTL input high than to
pull it low if you want to do things properly.

You write to the mode register to make some ports outputs. Those lines
now all go low, pulling any TTL inputs driven by them low. You now
write to the apporpriate port lines to make them high again, perhaps.
But there's still that little glitch when the line has gone low.

Better to either leave the port lines unaffected by a write to the
mode register (so you can pre-set them to 1's if you want to) or at
least force them high on such a write.

ARGH!!!





>
>
> On the other hand, Motorola did not modify their chips for the next major
> one.  Instead, they redesigned from scratch.  It took a little longer, and
> all software had to be rewritten, but they consistently ended up with THE
> BEST chip ("ichiban").
>
> The 6809 was THE BEST 8 bit processor.  But, marketing??
> They handed it to Radio Shack who decided it would be a cartridge based
> home games machine, with chiclet keyboard, RF [ONLY] video, and minimal
> expansion capability.   Users hacked around those limitations.

That is a very unfair comment. The design of the CoCo owes a lot to
the 6883 SAM chip, or perhaps the 6809E/6883/6847 'chipset'. There is
a Motorola application note showing how to use those 3 chips together
(along with ROM, RAM, etc) and both the CoCo and the Dragon were based
on that.

Radio Shack did get one thing right. They chose OS-9 rather than Flex.
OS-9 is a very elegant multi-tasking system. Flex is much the same as
CP/M and wastes the 6809.

I often wish that the BBC Micro has been 6809-based, the 6502 is the
only let-down in the design of that machine. Acorn did make a 6809 CPU
board for their Eurocard rack systems, I have no idea if it pre-dated
the BBC micro though. And Acorn, for some unknown reason, used Flex.

IMHO what killed the 6809 was that it came out rather too late and
there was no 'normal' application software for it. No word processor
or spreadsheet. As a result desktop computers using it were uncommon.

But it turns up all over the place in embedded systems. Those HP disk
and tape units, both the HPIB ones like the 9133 and the HPIL one,
9114. Almost all have a 6809 inside (the exception is the 9145 tape
drive which has a 68000). The HP1630 logic analyser, again there's a
6809 in there, along with the 6829 MMU chip. I've just repaired  a bit
of lab equipment with a 6809 in it. Got a monochrome graphics terminal
here made by Pericom. Graphics use a 7220 chip, but overall there's a
6809 to control it.

-tony