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List:       classiccmp
Subject:    RE: DLV11-J RS-232 Cable
From:       "Mark Csele" <mcsele () niagaracollege ! ca>
Date:       2011-04-28 20:57:40
Message-ID: 4DB99C84020000E40001E188 () ncgwia ! niagarac ! on ! ca
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The DLV11-J has a ten-pin connector.  To use with RS-232, simply use pin 2 as ground, \
pin 3 as TxD, and pin 8 as RxD.  It is also necessary to jumper pin 7 to pin 9.

The reason for the jumper: the receive input of the DLV11 is differential: it could \
work with RS-422 as well as RS-232.  RS-422 uses two wires for Tx and two for Rx and \
these are differential ... it is the polarity of the lines relative to each other \
that sets the bit (whether it is a one or a zero).  These "twisted pair" signals are \
very immune to noise and are used industrially for long runs.  I was always taught \
that anything over 20 feet should _not_ be RS-232 but a differential standard \
instead.

Anyway, grounding the "minus" differential receive input makes the "plus" \
differential receive input single-ended so that it is now referenced to ground: a \
voltage on that pin "positive" with respect to ground is a zero while a voltage which \
is "negative" is a one.  This is the EIA standard used for RS-232 ... it is bipolar \
(i.e. the voltage can swing negative or positive with respect to ground).

So, for a small system where the terminal is close, RS-232 works fine and a simple \
cable will suffice.  Where a system is large and terminals are placed a fair distance \
from the machine, RS-422 should be used.


Professor Mark Csele, P.Eng.
Niagara College, Canada
300 Woodlawn Rd., L-23
Welland, ON, L3C 7L3

(905) 735-2211 x.7629
E-Mail: mcsele@niagarac.on.ca
URL: http://technology.niagarac.on.ca/people/mcsele
Author of "Fundamentals of Light Sources and Lasers", Wiley, 2004


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