Path: utzoo!utgpu!news-server.csri.toronto.edu!mailrus!ncar!boulder!hibachi!rainer
From: rainer@hibachi.colorado.edu (Rainer Malzbender)
Newsgroups: comp.sys.m68k
Subject: Re: 680X0 dream machine
Message-ID: <19699@boulder.Colorado.EDU>
Date: 14 Apr 90 23:46:11 GMT
References: <105@motto.UUCP> <19620@boulder.Colorado.EDU> <1990Apr12.233111.3455@csuchico.edu>
Sender: news@boulder.Colorado.EDU
Reply-To: rainer@boulder.Colorado.EDU (Rainer Malzbender)
Distribution: usa
Organization: University of Colorado, Boulder
Lines: 37

In article <1990Apr12.233111.3455@csuchico.edu> garlick@csuchico.edu (Jim Garlick) writes:
>This is wierd, but aren't there literally tons of S100 IO cards and
>busses out there that can be had for next-to-nothing? 
>	...

I've actually built up a 68K system doing this, except I modified the
S100 bus assignments and just used the available cheap wire-wrap boards
and backplanes (got 'em for free, that's why I did this, it was supposed to
be the world's greatest synthesizer). Anyway, for *this* type of project
(homebrew high-end graphics Unix workstation) the S100 bus is woefully
inadequate. First of all, all the stuff we (I ?) want on the motherboard
wouldn't fit on an S100 card. Secondly, the S100 is not a 32-bit bus.
Thirdly, it uses cards with on-board regulators, requiring an 8 volt supply
whereas we can buy PC-style +5,+-12 supplies more cheaply. Fourthly, my
experience with S100 goes back to the late seventies, so I don't know what
kinds of boards are still being made, but I doubt you'd find anything
all that useful for this kind of project. Fifth, I hate the S100 form factor,
since it really requires a bulky chassis.
	Having as much circuitry as possible on the motherboard will be
cheaper than having to buy a bunch of cards. Peripheral Technology's
PT68K-2 (see MicroCornucopia, Nov-Dec '88) was a nice idea for a 68000
motherboard using the PC (not AT) bus, but it's a little wimpy now. Using
the AT bus might be OK, but if everything is on the motherboard (I mean
everything - GPIB, Midi, audio, SCSI, graphics, memory, floppy controller,
transputer link, Ethernet, for starters :-) what kind of AT boards do you
need ? I see the bus as a way to add more homebrew stuff later, as people
come up with ideas and needs, so we might not need to use a standard bus.
Lots of people use stock Amigas and ST's without using the bus, but I think
there should at least be one. I guess the other alternative is to have a
very simple and cheap motherboard and put everything on cards and let people
buy what they needed.
	Would someone who knows about the NS532 project please post
something ? I hate reinventing the wheel (although I do it all the time :-)
--
Rainer 'rhymes with miner' Malzbender          Just another Unix/C demagogue.
Dept. of Physics              (303)492-6829       rainer@hibachi.colorado.edu 
U. of Colorado, Boulder, USA                malzbender@opus.vaxf.colorado.edu