[ILUG] house wiring - serial over cat-5

[Geoff Moore]

You can put pretty much anything through Cat5 (remember we're basically just
talking about "wire" here), it depends on what performance you want out of
it.

You could run RS232 through mains cable if you wanted to (as long as you
didn't need any hardware flow control...'cos there wouldn't be enough
cores).

RS422, RS423 and RS485 are all flavours of differential serial data.

RS232 is single ended serial.

This means it has one wire for each signal which wiggles up and down
relative to a reference ground.

Differential serial wiggles two signals relative to each other and hence
isn't as susceptible to noise and doesn't rely on any fixed reference
remaining stable or noise free.

OK, CAT5 is arranged in pairs and the pairs are twisted together. The idea
is (simply put) that you put two halves of a differential signal on a pair
so that any differential noise is likely to be picked up on both wires and
hence will cancel itself out.

There are specified distance restraints for all serial transmission
standards. The differential types are all 1km.

RS232 is a lot less because it's so susceptible to noise. I can't remember
what the actual spec says but 25m is on the outer edges of what's "allowed".

Now, if you use lousy cable and you place it in a very noisy environment you
aren;t going to make anywhere near 25m. If you use cable that reduces the
picked up noise level on the signals then you're going to get better
performance and stretch the distance (to an extent).

If you're using CAT5 I'd recommend you choose which cores you use so that
you don't put RX data and TX data on the same twisted pair for instance as
they will couple onto each other.

But as the distances increase you're into the realms of luck. All you need
is for your dangly cable to run past the your old fridge or some other
'orrible noise source and your connection will start getting unreliable.

Best results will be obtained with screened twisted pair, with the screen
grounded, grounded backshell D Types and sensible selection of which cores
you use for which signals.

...but miracles you cannot work simply by using more expensive wire



Geoff Moore
====================================
Straight Forward Solutions Ltd
Maynooth Road, Prosperous,
Naas, Co.Kildare, Ireland
Phone : +353 (0)45 892739
Fax : +353 (0)45 893880
Mobile : +353 (0)86 8179683
email : geoffm at straight-forward.com
====================================

> -----Original Message-----
> From: ilug-admin at linux.ie [mailto:ilug-admin at linux.ie]On Behalf Of John
> P. Looney
> Sent: 26 April 2001 21:26
> To: irish linux users group
> Subject: Re: [ILUG] house wiring - serial over cat-5
>
>
> On Thu, Apr 26, 2001 at 08:00:53PM +0100, kevin lyda mentioned:
> > can i run serial devices over cat-5?  namely a vt220 terminal.
> total wire
> > length is about 7 to 25 meters.
>
>  RS424 (or something like that) will run over something like CATV. Anyone
> care to discuss what it can do ?
> \
> Kate
>
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