[Coco] 80 column pak prototype

Wed Oct 23 15:09:55 EDT 2013

On Wednesday 23 October 2013 14:32:26 Luis Antoniosi (CoCoDemus) did opine:

> I'm taking both grounds top/bottom through a via. Ain't this enough ?

As a ground, and in my probing, its not a very good ground.  The cartridge 
ear clips are much better & quieter grounds.

How much ground bounce will be impressed on that cartridge port pin ground 
depends on whats out there plugged into that port.  With a late coco3 
patched mpi out there, ground bounce in the mpi can exceed 2 volts with the 
ears plugged in!  I added some additional power buss bypassing, and several 
runners of solder wick, in spaghetti for shorts protection, from various 
points back to the boards ears, and got the bounce down into the 200 
millivolt range, and my mpi, nor anything plugged into it has made a data 
mistake since.  I also sawed the solder plated contact edge off and put a 
gold plated replacement on it, but that didn't stop all the errors, the 
extra bypassing and grounding did.  The ground busing in the late mpi looks 
as if it was added as an afterthought when laying the board out as its 
quite circuitous in getting to where its needed.  Some parts on the later 
mpi have ground connections that are at least 16" of trace getting back to 
the cartridge port.  With my mods, 6" max.

One thing that may have a bearing, my coco3 has a 63C09 in it, and the rise 
and fall times of the 63C09's signal edges are at least 5x faster that any 
6809 I ever stuck a scope probe on.  I get the impression that if we rigged 
a downclock /4 for the rest of the machine to put the video back to normal 
speeds, that 63C09 could run very happily at 20+ megahertz when it wasn't 
waiting for the external stuff to wake up.  John Kowalski's speed kit on 
steroids.  Signal edge rise and fall times are A, to within millivolts of 
both supply rails as its cmos, and B, well under 20 ns.  For a coco, that 
is not fast, its damned fast!  The 68B09 in the coco3 might make that same 
10 to 90% swing in 110 ns.  But the logic 1 state is only about 3.28 volts, 
not 4.98 running from a 5.05 volt rail.  The noise immunity just from that 
is many times better.  At the same time, those rise & fall times also make 
circuits a foot away ring like the liberty bell, but without the cracks, so 
its a mixed blessing that will bite the unwary pcb designer where it hurts.

> On Wed, Oct 23, 2013 at 2:12 PM, Gene Heskett <gheskett at wdtv.com> wrote:
> > On Wednesday 23 October 2013 14:06:56 Mark Marlette did opine:
> > > Luis,
> > > 
> > > Fun stuff!
> > > 
> > > On the note of strange characters. As it appears that these
> > > proto-boards are a good thing, they are not good for digital design
> > > at MHZ rates.
> > > 
> > > The CoCo's address bus is not buffered, unless you have a
> > > Pro-Tector+, so just driving through the ribbon cable to your board
> > > will be degraded. My tests shown ~3-4" was max, YMMV.
> > > 
> > > The proto-board adds capacitance to every point, some cases that is
> > > good, most cases it is not.
> > > 
> > > So your circuit can be wired electrically correct and it still will
> > > not work just by how you physically built it. That is not to say
> > > you don't have a wiring issue. :)
> > > 
> > > Generally it is cheaper and will yeild better results to have a
> > > board made.
> > > 
> > > My $0.02.
> > > 
> > > Any case, enjoy and continue your great work on the software and
> > > hardware!
> > > 
> > > Regards,
> > > 
> > > Mark
> > > http://www.cloud9tech.com
> > 
> > And I'll throw in another 2 cents, Mark.  This board is dependent on
> > the single ground pin in the socket connector.  It is not a very good
> > ground.
> > 
> > I'd at least try adding another wire from the ground bus on the board
> > back to one of the clips that grab the grounding ears of most boards,
> > one on each side of the socket proper.
> > 
> > > ________________________________
> > > 
> > >  From: Luis Antoniosi (CoCoDemus) <retrocanada76 at gmail.com>
> > > 
> > > To: CoCoList for Color Computer Enthusiasts <coco at maltedmedia.com>
> > > Sent: Wednesday, October 23, 2013 6:52 AM
> > > Subject: [Coco] 80 column pak prototype
> > > 
> > > 
> > > Hi all,
> > > 
> > > Having all the components at hand I started prototyping yesterday:
> > > 
> > > pic.twitter.com/aAnpm39NwL <http://t.co/aAnpm39NwL>
> > > 
> > > One hour later:
> > > 
> > > pic.twitter.com/dOEpz5Y91K <http://t.co/dOEpz5Y91K>
> > > 
> > > And turning this thing on:
> > > 
> > > pic.twitter.com/rl4fNtssfa <http://t.co/rl4fNtssfa>
> > > 
> > > You can see some characters are strange, I must have swapped a bit
> > > in the data bus or something. It was too late yesterday to
> > > troubeshooting but HEY IT WORKS!
> > > 
> > > Those protoboard jumpers are really helpful. :)
> > 
> > Cheers, Gene
> > --
> > 
> > "There are four boxes to be used in defense of liberty:
> >  soap, ballot, jury, and ammo. Please use in that order."
> > 
> > -Ed Howdershelt (Author)
> > 
> > File cabinet:
> >         A four drawer, manually activated trash compactor.
> > 
> > A pen in the hand of this president is far more
> > dangerous than 200 million guns in the hands of
> > 
> >          law-abiding citizens.
> > 
> > --
> > Coco mailing list
> > Coco at maltedmedia.com
> > http://five.pairlist.net/mailman/listinfo/coco

Cheers, Gene
-- 
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)

QOTD:
	I looked out my window, and saw Kyle Pettys' car upside down,
	then I thought 'One of us is in real trouble'.
		-- Davey Allison, on a 150 m.p.h. crash
A pen in the hand of this president is far more
dangerous than 200 million guns in the hands of
         law-abiding citizens.