homebrew 'puter project (was: 8008?

[Roger Merchberger]

Rumor has it that Chuck Guzis may have mentioned these words:
>On 11/16/2005 at 11:54 AM Roger Merchberger wrote:
>
> >Originally I was going to design and build my own buss structure /
> >backplane ( I was thinking 80 pins - 40-pin IDE headers are bog-easy to
> >find... ;-) something that could expand to a 16-bit CPU....
> >
> >First card would be a fully buffered CPU, next card might be 256K or 512K
> >RAM, 3rd card might be a small LED/LCD display (2x40 or somesuch) and of
> >course, one card full'o'blinkinlights... ;-)
>
>Why have a backplane at all?  That much RAM is what, one or maybe two
>chips?

How else could you pull a 6809 card, stick in a 68K card, and still use the 
same RAM / keyboard / etc.? Or pull out one ROM card (say, running OS-9) 
and put in another, running something else. ;-)

>Better than a backplane/bus, why not just a good I/O connection?  A nice
>serial hookup maybe?

Expandability - I eventually want to be able to build D/A \ A/D hardware, 
keybaord interface(s), dual serial interfaces, I/O ports, maybe a floppy 
interface, etc... Modularity can be a wonderful thing sometimes...

I have this weird tendency to over-engineer stuff... ;-) However, that has 
served me well over the years; at least I don't have to *re-do* most of the 
stuff I've done.

>More than fast enough for blinking lights and LCD displays.  Why burden the
>CPU-to-memory datapath with yucky bus interface hardware?

Dunno enough about 68Ks (yet) but 6800/6809 CPUs only have memory-mapped 
I/O, so all that's needed is to buffer the lines (unless you're feeling 
particularly foolhardy, like on the CoCo) and address decoding. Not exactly 
a *lot* of hardware, as it were...

Besides, a secondary reason for building this is to put it in a 
plexiglas/lucite case so it'll work as a functional display piece - I've 
been doing some volunteer work with the local schools about "how computers 
actually work" - A single board with an AVR & a few LEDs just doesn't seem 
so impressive (or fun!) ;-)

'Course, with my track record, it'll prolly not happen until I retire, but 
what the heck... a guy can dream, right? ;-)

Laterz,
Roger "Merch" Merchberger

--
Roger "Merch" Merchberger   | "Profile, don't speculate."
SysAdmin, Iceberg Computers |     Daniel J. Bernstein
zmerch at 30below.com          |