EIA 232 vs. 422, Color Computers (was Re: Serial floppy drive s)

From: Dwight K. Elvey <dwightk.elvey_at_amd.com>
Date: Thu Sep 12 18:02:00 2002

>From: "Jeffrey Sharp" <lists_at_subatomix.com>
>
>On Friday, September 6, 2002, Davison, Lee wrote:
>>
>> > That's not true. Serial cable can go for a good many feet before
>> > the signal breaks down (someone should pipe in with actual data ;)
>>
>> 450 feet at 9600 bps through multi strand sheilded cable. This was
between
>> two buildings and ran through a drain to get under a road. 19200 bps was
>> tried but was error prone. dropping the speed to 9600 bps worked.
>
>100 feet at 115200 bps through three unshielded wires, wrapped around a
>three-foot-tall Jacob's ladder apparatus enclosed in plexiglass. No bit
>errors. We gave up and decided to build a device to simulate bit errors.
>

Hi Jeffrey
 What makes you think that wrapped on the outside of a Jacob's
ladder has either the right coupling or the right frequency
spectrum to effect a RS-232 signal? Arbitrary test like this are
not real world test and only impress those that don't understand
what it takes to interfer with a particular signaling method.
There are books written about how to test for interference.
Looking at impressive sparks will sell P.T. Barnum's
"one every minute" but not me.
 The environment I used the RS-485 in had RS-232 running at
4800 baud and was seeing error burst on the order of
1 in every 1000 or so bytes. The lines were not any
longer than 20 feet. It was more the type of noise
source that was important. One needs to know the right
spectrum and how the energy was coupled. I wouldn't
have expected the Jacob's ladder connected as you
described to have introduced hardly any energy in the
right form.
Dwight
Received on Thu Sep 12 2002 - 18:02:00 BST