Re: Ribbon Cable

On 2013-12-17, at 19:16, Jim Brain <brain@jbrain.com> wrote:

>> If the SX-64 problems with the new carts (or carts problems with SX-64) indeed stem from the ribbon cable - Replacing the original ribbon with one having twice the number of wires and grounding every other one should immensely improve the situation.
> 
> Since I have an SX open on the bench right now, I looked at the ribbon cables (2).  The one for the user port might have this arrangement, since it's about 40 pins for a 24 pin port.  The expansion port, on the other hand, is 50 wires for a 44 pin port.

I don’t think there were connectors for 50 pin (like the SCSI ones) but for doubled wire-count cables as in the 80-wire PATA (40 pin connectors for 80 wire cable), were there? That would be an easy solution if there were...

>> Just one more question: at some point (shortly before SATA became prevalent), instead of flat ribbons, thick round cables for PATA connection became fashionable. If the whole thing was about intertwining signal lines with GND - wouldn’t rolling the whole cable into a round sleeve just ruin the whole idea? How is that?
> 
> I have one of those cables.  I seem to recall each "pair" was twisted, so each signal had a ground wire wrapped around it.

Those I have don’t, but as Gerrit corrected me - it makes sense: there was no intertwining on the original PATA (typical PC crap engineering - like with most PC stuff when compared to the rest..)

>> Yes, regular SWR stuff. Like with every antenna feeder, but.. still what frequencies we talk about in an SX-64? The assumed wavelength is in meters range there. I tend to think that it would have to be really badly off charts to cause problems on digital levels. Maybe - as suggested here - it is more of PWR problem. I guess the PSU supplies enough but am not sure about the path (length, capacity).. This is easier to check though.
> 
> With all due respect to Bill,  think issues develop far below hundreds of MHz.
> 
> 	• THere is no buffering on most of the exp port signals.  They are straight from the CPU
> 	• Weak drivers (in my opinion).  Thus, any degradation of signal is a major concern, as is any cap/ind loading.
> 	• The exp port is not 1MHz, in my opinion.  I think the relevant "timing cycle" is the time when the 6510 gets off the bus and the VIC-II gets on the bus.  If that is 20ns (and I think it is less), then I think that defines the timing.  20ns is 50MHz...  It's probably a bit longer than that, but coupled with the above, I think problems could develop at far lower speeds.
> Maybe this is the reason to break down and get a PC scope, so I can capture some signals from the two machines and post pics of the differences.

That would be very good. My bench is currently flooded with other things and that’s why it’s not really a feasible option for me ATM. If you could do this - that would be great. I think it could shed a lot of extra light on the problem.

-- 
SD!
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