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From: knudsen@ihwpt.UUCP (mike knudsen)
Newsgroups: net.micro,net.arch,net.micro.6809
Subject: Architecture, or Coincidence?
Message-ID: <482@ihwpt.UUCP>
Date: Wed, 25-Sep-85 18:33:48 EDT
Article-I.D.: ihwpt.482
Posted: Wed Sep 25 18:33:48 1985
Date-Received: Sat, 28-Sep-85 04:32:40 EDT
Distribution: net
Organization: AT&T Bell Laboratories
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Xref: watmath net.micro:12106 net.arch:1822 net.micro.6809:506

(Re-Reposted due to more machine-changeover foulups)

Is this just cultural coincidence, or was there a hardware
reason for the following: In home computers, descendants of
the 8080 have aimed at "serious business" TEXT-ONLY applications,
whereas the 6800's descendants' machines have featured 
bit-mapped color graphics and sound to a much greater extent.
To list examples of these descendant micros and their computers:

	8080				6800
	----				----
	Z80				6502
TRS-80 Models I-IV,		Apple II, Atari, Vic-20, C-64
CP/M systems				6809
				TRS-80 Color Computer

	8086,-8				68000
IBM PC and 1001 clones		Apollo, Mac, Atari-ST, Amiga,
				AT&T 7300 (can run text-only)

Sure puts most of the decent graphics into the right-hand
side, doesn't it?  Yes, there are exceptions -- the Z80-based
Exidy Sorcerer and the 8080 CompuColor,
and now that business types have discovered graphics
you can get hi-res color on the IBM-PCs.  But from 1977 thru '83
the picture is pretty lopsided.  And it's not just marketing --
the TRS-80 and Apple II were both supposed to handle games and
hobby-hacking, AND science and business.  

As for the latest machines:  while you can use
an IBM-PC for years w/out graphics, you can't even *talk to the
OS* on the 68K machines listed without clicking a mouse!
Ever see a text-only Mac?  Want to?

I suspect part of this is due to the equivalence of processor cycles
and bus cycles in the 6800/6502/6809 chips.  During the first half
of each cycle, the bus is unused by the micro, so the designer
could sneak a free DMA timeslot on every cycle for refreshing
video graphics from RAM, without slowing down the processor.
(This also makes for easier DRAM refreshing).

This trick was well-known to 6502 hackers (eg, Hal Chamberlin)
and was institutionalized by Motorola in their graphics chip set
for the 6809 (the applications note for these chips became the
Radio Shack Color Computer).  The 8080-type micros, with their
irregular bus-access subcycles, could NOT use this scheme;
unable to DMA the large RAM areas needed for bitmap graphics,
the Z80 boxes had to stick with separate, small, text-only
display memories.

Interesting how subtle hardware features of a micro can influence
the architecture and hence end uses of its computers.
Open for commentary -- mike k
	ihnp4!ihwpt!knudsen


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