[Coco] Multipak redesign/replacement

[Gene Heskett]

On Monday 23 February 2015 08:56:12 pm RETRO Innovations wrote:
> On 2/23/2015 12:36 PM, Gene Heskett wrote:
> > And I am NOT in favor of duplicating whats in the later ones as a gal, it
> > is so slow at the gate buffer direction turnaround time that a truly
> > serious logic short exists in mine for about 100ns as it does that.  Both
> > the ground and power rails are bounced, as much as a volt, destroying the
> > logic circuits noise immunity, by having both buffer directions enabled
> > for a short period of overlap. That no doubt also contributes to the
> > power used, and the chip temps. I do not think the 26-3024 design
> > suffered from this problem, so its straight ttl logic must have been
> > faster than the gal used in the 26-3124.
>
> I'd love more detail on this.  Not sure the speed of the 14L4 in the
> 3124, but I would think the 14L4 is a -20 or similar part.

Whatever speed it is, by the time the bus turnarounds get to the chips, its 
one both direction for long enough to cause a logic short, bouncing the 
supply rails by a volt of more each.

> > It is, from the image I have, apparently all one long board, rigged with
> > a 40 pin cable between two IDC headers to plug it into the coco. So the
> > packs are rotated 90 degrees, all still standing up so we'd see them from
> > the edges.  With _good_ high resolution drawings in hand, the ones I was
> > able to download aren't, this could be laid down so the carts all
> > projected to the rear, getting much of the I/O cabling down out of sight
> > a lot better than now.
>
> I am dubious that the 40 pin IDC cable would work.  As I recall, that
> design was not proven to be working.  The Commodore SX64 uses a similar
> flat ribbon cable for the expansion port that sits on top of the
> machine, and it's been known for decades that the cable is the reason
> many cartridges do not work with the SX, but do with the 64
>
> > But without locating Paul Barton, aka BartSr on some forums, so that his
> > original hi res work can be obtained, this project is equally dead in the
> > water.  And I do apologize to all for getting the hopes up.
>
> Do you just want an 8 slot board design?  I was considering morphing the
> design on the PC right now into an 8 slot design, but it does contain a
> CPLD (-7ns) and uses HCT logic.
>
> Jim

That does sound doable.  Can I help?
>
> --
> RETRO Innovations, Contemporary Gear for Classic Systems
> www.go4retro.com
> store.go4retro.com

Cheers, Gene Heskett
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