News Group Posts

serial printer flow control crosstalk cross-talk

capacitance which pair to use

From: bv@wjv.comREMOVE (Bill Vermillion)
Subject: Re: Print Job Stuck in Queue, Must Reboot Server
References: <c7e5acb2.0210070806.2c36b1cd@posting.google.com>
<c7e5acb2.0210081038.704d581a@posting.google.com>
<ce18qu4s9s9r1197p4dnqmvjtusk41puq5@4ax.com>
<56fe3a2b.0210091232.150c8c7e@posting.google.com> 
Date: Thu, 10 Oct 2002 16:27:13 GMT

In article <56fe3a2b.0210091232.150c8c7e@posting.google.com>,
Dan Martin <dcmartin@affinitycorp.com> wrote:
>Jeff Liebermann <jeffl@comix.santa-cruz.ca.us> wrote in message news:<ce18qu4s9s9r1197p4dnqmvjtusk41puq5@4ax.com>...
>> On 8 Oct 2002 11:38:02 -0700, jaykchan@hotmail.com (Jay Chan) wrote:

>> >Jeff Liebermann <jeffl@comix.santa-cruz.ca.us> wrote in message news:<std3qu0vnbs5lrcvqr84fq38v9gc8m3p3s@4ax.com>...


>> No.  I use CAT5 for everything.  However, you have to be careful in
>> selecting which wire to use for what purpose.  If you selected a
>> twisted pair to act as RX and TX lines, you will get the worst case
>> crosstalk with a general loss in reliability.  Out of 8 wires, I
>> suggest you pick one of a pair for RX, one out of another pair for TX,
>> and ground the unused wires from the RX and TX pairs for the signal
>> ground.  Do NOT wire the common "protective" ground (pin 1) as you
>> will probably end up with a ground loop full of AC 60Hz crud.

>Yikes!  I've always gone out of my way, when using cat5 in a serial
>application, to be sure that Rx and Tx were on the same twisted pair.
>This is true of cat 5 network cable, is it not?  pins 3 & 6, tx/rx, 
>usually green/white-green.  No?

In addition to what Jeff has said let me mention this.

Twisted pair is mostly used in balanced line configuration - eg
there is a positive and negative wire.   RS232 does NOT used this
method.  There is one wire for each signal and a common return
ground for all signals.

>I assumed that a signal on Blue would not adversely affect the
>White-Blue wire since they are twisted. (Blue/White-Blue being 4
>and 5 on the rj45; the center pins being rx and tx for rs-232?)

In a balanced line that assumption is correct - in single line
no. You could cause more interference on twisted with different
signals than you might with straight parallel wires


Twisted pairs are used to reject common mode [EMF] signals.  These
are low frequency signals typically induced by power lines, etc.

The twist means that outside inteference will be the same for both
sides of the line and cancel itself out.

The other side of the wiring world is shielded.  That reject the
high-frequency components.   
-- 
Bill Vermillion - bv @ wjv . com
 

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