CUBIX/6809 updates - small system / bus choice

Gooijen, Henk henk.gooijen at oce.com
Tue Dec 13 13:20:57 CST 2005


The Dr. Neherlab (of the Dutch Telecom, PTT) had in the end of the 70ties their
own developed bus system. I was there and have such a (6800)based system
still in the attick. My first home-built system, 1978).
There were 8k bytes (with 2114) memory cards, 16k (2716) EPROM cards, and
*different* CPU cards. I remember the 6800-based (obvious), but there was also
a Z80-based card. Keep the memory boards in the backplane, swap the 6800
for the Z80 CPU card, and the system works (with other software of course).
To be that versatile, the CPU boards had extra logic to make the bus interface
always working (for example, the 6800 is synchronous in the bus transfers).
 
Their system used the DIN41612 connectors (IIRC), It is the same connector
used on VME modules, and has 32 pins in one row. With the 2- or 3-row version
you have sufficient pins (96) for even a 68000-based bus system.
That system also carried the power supply over the bus. I remember that pin #1
and pin #2 and pin #31 and #32 were used for +5V and GND.
Hell, why not use the VME 3-HE bus pin designation for you own design?
 
If you want a reliable, robust system, do not use card edge connectors.
The VME connectors are superior. Besides, Eurocard boards with at one short
edge drilled holes for DIN41612 3-row is pretty standard stuff. And if you want to
build a small system, and have "dedicated" card for memory, (flash)ROM, and
do not forget I/O !! - my humble opinion is Eurocard is the best choice.
BTW, the female 3-row counterpart for DIN41612 also exists in a version to connect
to flat cable! So, take some 20 cm of flat cable and pinch that female part on the
flat cable, et voilà, you have the backplane / bus !  For improved noise immunity
perhaps not the best solution, but then it is fairly cheap that way.
 
my 2 (euro)cents,
- Henk, PA8PDP.

________________________________

Van: cctalk-bounces at classiccmp.org namens Roger Merchberger
Verzonden: di 13-12-2005 19:03
Aan: General Discussion: On-Topic and Off-Topic Posts
Onderwerp: Re: CUBIX/6809 updates



Warning: I did not top post! There are further responses inline with the
reply. ;-)

=-=-=-=-=

Firstly, I'd like to mention that I've always wanted to build my own
homebrew 6809 system... altho I've been thinking of designing my own buss
system (around 80 pins or so) so other CPUs could be used if desired. I was
thinking of a multi-board system with a 6-7 socket backplane. I want it to
be educational to others (read: see-thru Lucite case & lotsa Blinkenlights!
;-) at the same time that I learn from it, too.

For a few reasons, S100 is not an option: I want the system smaller /
easily portable (I'm guesstimating in inches: 6x6x9, with an external 5V
only switcher), and I also want it to be easily buildable by a hobbyist.
Trying to dremel an S100 cardedge would seem to be quite a bit of work for
not a lot of gain - but square boards with a pair of 40-pin IDE connector
(for example) edge-soldered on would be pretty easy to do at home.

I do have a question:

Are there any 80-100 pin buss structures already in use I could copy that
might fit my bill? I'd rather do something that might be compatible with
something else out there if it's similar enough to what I want to accomplish.

I'm hoping to take lots of pictures & basically make the design free on the
web as I do this, mainly to show people if an idiot like me can make a
computer, so can you! ;-)

Oh, and for the record: Cubix looks *kewl*. ;-)

Rumor has it that Scott Stevens may have mentioned these words:
>On Sun, 11 Dec 2005 20:15:48 +0000
>"Dave Dunfield" <dave04a at dunfield.com> wrote:
> > > I think cubix was a good idea, but this 15 years too late for
> > > me as I
> >
> > What a co-incidence ... CUBIX is 20+ years old, so it should
> > have been perfect :-)

And it's never too late for good ideas. ;-)

> > > realize in hindsight that 128k of
> > > memory - split code and data is needed for any real work.

Them's fightin' words. 64K w/OS-9 got me thru High school & my first year
of college, before I got my CoCo3 & 128K (later to 512K) but I still had a
maximum 64K code space - and that kept me working until the mid-90's. Other
than running (crawling) Autocad, my '386 was the 'toy' and my CoCo was the
workhorse. Once I got an EISA 486-66 server from my (then current)
employer, did I consider the CoCo my secondary machine.

> > > This the  crummy 8088 has but not the 6809.
> >
> > Funny, I've done LOTS of "real work" in <64k 8-bit CPUs. Even
> > now a lot of my command line utilities are compiled in 64k
> > "tiny" model (Referencing stuff known here, Anyone notice that
> > ImageDisk, my Simulators and the various other transfer
> > utilities that I've done are all .COM files) - I used to think
> > 64k was lots of memory... and I still do!

Unless you're running Windows. ;-)

>64K is a HECK of a lot of memory if your code is all in assembly.
>I've worked on projects where the limited program memory in the
>micro, i.e. the 16K of program memory available on-chip, was a
>godsend- it served as a brake on futher 'feature creep' requests
>from the folks in marketing.  ("yes, we can include new feature
>'x' but it means doing away with the lookup table that feature 'j'
>you requested last month uses.")

A few of those microcontrollers have 128K of flash on 'em now.

I want my CoCo on a chip! ;-)

Laterz,
Roger "Merch" Merchberger

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



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