Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uunet!sci34hub!gary
From: gary@sci34hub.UUCP (Gary Heston)
Newsgroups: comp.dcom.lans
Subject: Re: RS232 cable
Message-ID: <789@sci34hub.UUCP>
Date: 30 Oct 90 15:19:10 GMT
References: <2404@gould.doc.ic.ac.uk>
Reply-To: gary@sci34hub.sci.com (Gary Heston)
Organization: SCI Technology, Inc., Huntsville, Al.
Lines: 38

In article <2404@gould.doc.ic.ac.uk> epl@doc.ic.ac.uk (Edward Peter Lennon) writes:
=Hello netters-I have a query about the rs232 communications.In William Stalling
=book"local network technology"Third edition page 48 it has the following RS232
=limits.
=Data Rate(bits/s)                     Distance(meters)
=1.2k                                    914
=2.4k                                    549
=4.8k                                    244
=9.6k                                    122
=Source Texas Instruments.
=The above rates and distances are available on RS232-C designed cable
=1-What exactually is RS 232-C designed cable

Ain't nonesuch. I stepped over to the microfil machine and checked. There's
not one word in the spec which designates a cable. There are, however, 
specific characteristics that should be met for a circuit regarding 
impedance and capacitance.

=2-Where did I get the figure of 50 foot maximum distance for RS 232 communications from.
=maybe a special type of cable,or maybe the book is wrong.

From the EIA RS232C spec, page 8, paragraph 3.1:

" ... The use of short cables (each less than approximately 50 feet or 
15 meters) is recommended; however, longer cables are permissible, 
provided that the resulting load capacitance (CL of Fig. 2.1), 
measured at the interface point and including the signal terminator,
does not exceed 2500 picofarads. ... "

So, using good, low capacitance cable, you can run longer distances.
Most people pretty well ignore the limitation, anyway; I run a couple of
hundred feet regularly.

-- 
Gary Heston System Mismanager and technoflunky uunet!sci34hub!gary or
My opinions, not theirs.  SCI Systems, Inc.     gary@sci34hub.sci.com
  The sysadmin sees all, knows all, and doesn't tell the boss who's
  updating their resumes....  This .sig Copyright G. L. Heston, 1990