epl@doc.ic.ac.uk (Edward Peter Lennon) (10/30/90)
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
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.
Peter Lennon.chris@yarra.oz.au (Chris Jankowski) (10/30/90)
In article <2404@gould.doc.ic.ac.uk> epl@doc.ic.ac.uk (Edward Peter Lennon) writes: > 2-Where did I get the figure of 50 foot maximum distance for RS 232 >communications from. From the standard as published in 1969. It guarantees that it would work on this length of cable up to maximum frequency specified by the standard (which is 19,200 bits/s if I remember correctly) in high level of EMI, on a crappy unshielded, ribbon cable and with your senders using low voltage sources eg. 3.5 or 5V. If you use 12 or 15V or perhaps 25V (still within the spec) sources, shielded twisted pair cable you can have it working on lengths >1,000m, but formally it is outside the spec. We can be a little more adventurous these days knowing that 10BaseT allows us to run 10Mbit/s on unshielded twisted pair for up to ~50m (~165 feet or so). (:-)). Hope this helps. Caution: All figures above are from the top of my head and may be slightly off the mark. -m------- Chris Jankowski - Senior Systems Engineer chris@yarra.oz.au ---mmm----- Pyramid Technology Corporation Pty. Ltd. fax +61 3 820 0536 -----mmmmm--- 11th Floor, 14 Queens Road tel. +61 3 820 0711 -------mmmmmmm- Melbourne, Victoria, 3004 AUSTRALIA (03) 820 0711 Entities should not be multiplied needlessly. - William of Ockham, Razor of. (As sound as ever, but try to explain this to marketing people. - me).
gary@sci34hub.UUCP (Gary Heston) (10/30/90)
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, 1990henry@zoo.toronto.edu (Henry Spencer) (10/31/90)
In article <2404@gould.doc.ic.ac.uk> epl@doc.ic.ac.uk (Edward Peter Lennon) writes: >2-Where did I get the figure of 50 foot maximum distance for RS 232 > communications from. That's the max it is actually specced for, using garden-variety cable. Low-capacitance cable helps. Also, there is an important distinction between what is *guaranteed* to work and what you can usually get away with. RS232 runs of hundreds of meters are out of spec but usually work; modern receivers and transmitters are mostly much better than the minimum given in the spec. -- "I don't *want* to be normal!" | Henry Spencer at U of Toronto Zoology "Not to worry." | henry@zoo.toronto.edu utzoo!henry
howeird@hpspdra.HP.COM (Howard Stateman) (10/31/90)
epl@doc.ic.ac.uk (Edward Peter Lennon) writes: >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. You got that 50-foot rule from standard RS232 terminals specs, which were supported by a set of chips which would drive a +5v signal down 50 feet of wire. In real life, 75 feet was acceptable. Later chips were made to support 1000-feet connections, but technically these were RS423, I believe. Someone please correct me if I have the number scrambled. What resemblence, if any, these specs have to LAN cabling standards, is left as an exercise for the reader. Howard Stateman Systems Support Engineer Telnet (415) 857-3817 Intelligent Networks Operation, Palo Alto howeird@hpspdra.spd.HP.COM
pat@hprnd.rose.hp.com (Pat Thaler) (11/06/90)
> > We can be a little more adventurous these days knowing that 10BaseT allows us > to run 10Mbit/s on unshielded twisted pair for up to ~50m (~165 feet or so). > (:-)). > 10BASE-T allows up to 100 m on normal 24 AWG unshielded twisted-pair cable. The system requirements and design of 10BASE-T are fairly different from those of RS-232 and I don't think you can draw conclusions about what one can support in distance based on the other. For instance, RS-232 uses single-ended drivers and can be run over ribbon cable; 10BASE-T uses differential drivers and (because of its high frequency) should only be run over twisted-pair cable. Pat Thaler
jeff@perle.UUCP (Jeff Cole) (11/07/90)
In article <789@sci34hub.UUCP> gary@sci34hub.sci.com (Gary Heston) writes: > >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. ... " > Using the current rev. of the specification, EIA RS-232D, ( 1986 !! ), Page 11, paragraph 3.1 : "The maximum accceptable length of cables ( particularly the extension cable) is not defined. It is determined by the electrical requirement in Section 2.1.4". Sec. 2.1.4 basically says 2500 picofarads, among other considerations. This is really part of the issue of cabling LANs ( and I use the term loosely with respect to RS-232) in general, in which hard and fast rules are not possible to pin down, except under such conservative conditions that practically everybody would ignore them, because the system would "work" under less severe circumstances. Rules of thumb ( often disguised as "Site Planning and Preparation" documents ) are about the best that can be done. Individual sites will vary in terms of the cable type, length of runs, ambient noise levels, etc. This variation in site characteristics leads to variation in bit error rates for sites which aggressively cable. ( i.e. push the guidelines ). Eventually some sites will cable themselves in such a way as to cause operational problems. Good network management tools will help customers identify these problems, especially the ones that are not visible ( e.g. the network that loses one third of its packets, but can still run due to upper layer recovery mechanisms, at a significantly reduce throughput ). -- Jeff Cole 370 Tapscott Rd. Perle Systems Limited Scarborough, Ont. UUCP: ...!uunet!mnetor!perle!jeff Canada M1B 3C4 ( some ramblings about my opinions vs. company policy etc., etc. )