Re: Parallel Cables

["Mike Huggins" <mikeh@xxxxxxx>]

Yes I agree with Paul about the timing issue

>From memory and it is the deep and distant past, parallel needs 9
wires.
This could easily be wrong though !! 1 of them must be Gnd, so in theory
you
could use shielded CAT5 which would give you 8 wires + shield, and you'd
use
the shield as Gnd

I have seen people using parallel over longer distances than 30 feet, and
it
worked okay. But 30 is the recognised max

Mike


----- Original Message -----
From: Paul Gordon <paul_gordon@xxxxxxx>
To: <ukha_d@xxxxxxx>
Sent: 31 July 2000 19:07
Subject: Re: [ukha_d] Parallel Cables


> I was always of the impression that the problem with parallel cable
length
> is not specifically to do with voltage drop along the cable, but more
to
do
> with timing issues:
>
> A parallel cable transmits 8 data bits simultaneously. All 8 bits have
to
> arrive at the other end at "exactly" the same time (or
within a very
> specific tolerance of each other), in order for the byte to be
correctly
> received and understood.
>
> As the cable length increases, any difference in the electrical
properties
> between any of the 8 data lines causes varying degrees of
"latency" in the
> transmission time of each bit, and as the overall cable length
increases,
so
> this effect is exaggerated, resulting in the 8 bits arriving all at
> different times to each other.
>
> This is why serial cables can be driven so much further and faster
than
> parallel cables.
>
> Also, how could you run a parallel device over CAT5? - CAT5 only has 8
> cores, and parallel cables have either 25 or 36. - Not all are used of
> course, but I believe you ALWAYS need more than 8, as there are a
minimum
of
> 8 required for the data bits, plus "some more" for timing
& sync signals
> etc...
>
> 0.02p
>
> Paul G.
>
>
>
> >Here's an excerpt from my conversation with Blowback on IRC about
parallel
> >cables.
> >
> ><Stubbs> what is the maximum distance for a parralel cable?
> ><Stubbs> does anyone know?
> ><blowback> 30 feet
> ><Stubbs> hmmm, what's that in proper money :-)
> ><Stubbs> and would it be extended by using cat5 cable?
> ><Stubbs> I've got an LCD and want to put it in the lounge,
running off my
> >PC's parallel port.
> ><blowback> er, about 9m
> ><blowback> not sure about the cat5
> ><Stubbs> I'm guessing that because the device doesn't use as
many of the
> >wires as a printer does, the capacitence generated in the cable
will be
> >less, and therefore I can get a longer run, does that sound
sensible?
> ><blowback> I think voltage drop along the wire is going to
be more of a
> >problem than capacatitive coupling tho
> ><blowback> guess you'll have to try it and see!
> ><Stubbs> yeah.
> >
> >Is my guess right? Would using CAT5 make any difference?
> >----------------------------------------------
> >Stuart Grimshaw
> >Schoolsnet Ltd                         Special
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> >                www.schoolsnet.com
> >----------------------------------------------
> >
>
>
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