[Coco] Multipak redesign/replacement / New CoCo...

[Gene Heskett]

On Monday 23 February 2015 11:41:53 pm RETRO Innovations wrote:
> On 2/23/2015 10:18 PM, Gene Heskett wrote:
> > Oh look, all those flashing leds must mean its working right? ;-)
> > Actually, that is one feature creep I'd pay for happily Jim.  Their value
> > as a troubleshooting tool outweighs the cost IMO.
> >
> :-)
> :
> >> As for the other designs, the 8 slot unit was gargantuan, and I wanted
> >> something I thought would be of interest, challenging enough to allow me
> >> to learn this platform, but not so large as to be a debug nightmare.
> >> The MPI design looked fine, but I felt I could minimize TTL count by
> >> using a CPLD, and still provide the same functionality.
> >
> > I am sure it could, so all I'll mention is the additive delays can be a
> > nuisance.  Check those carefully.
>
> I'll post the schematic as soon as I finish, but I think all signal
> paths are ~9ns (2ns for the HCT buffers, + 7ns worst case in the
> CPLD).   CART, SCS, and CTS are handled directly in the CPLD, so no need
> for muxes or decoders like the 139s and the 157s in the MPI. So, 10nS
> should be worst case at 25C.
>
> The cable is a concern.  My google fu isn;t finding cheap shielded
> cables with at least 36 lines that are not significantly expensive (or
> have expensive connector requirements)

40 wire ribbon is supplied in 25 or 50 foot+ spools, and the connectors are 
all IDC.  The header pins soldered into the board are not that expensive, 
although I would opt for the gold flashed versions of both the header and the 
cable socket to improve the long term connectivity.

Shielding is optional as long as the FCC van isn't cruising your street. I 
would assume although I have not searched for it, that a silvered mylar wrap 
with a drain wire might be available on that same 25 or 50 foot spoolage.  
That, if tied to the ears pads, would go quite a ways toward keeping the 
radiated noise down.

Speaking of ears pads, those pcb's I have looked at do NOT make full use of 
that pad, the actual trace leaving the pad and connecting it to other ground 
plane points on the board, needs to be wider, as wide as there is room to 
make them.  Ditto the 5 volt rails, they need to be as wide as you can find 
physical room for them.

Cheers Jim, Gene Heskett
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