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'[EE] RS232 over CAT5'
2010\05\16@202656 by Josh Koffman

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Hi all. I'm working on a board that has a specific use at the moment,
but I'd like to leave things a bit open for other future uses as well.
At the moment, there will need to be a connector that talks to a
device via RS232. It's low speed (9600bps) and short distance (under
10 feet, likely under 3 feet). To keep my options open for the future
(and to aid my design), I'd like to use RJ45 connectors to carry the
RS232 signal. There is a standard for this (EIA-561, mentioned here
about 25% of the way down the page, but I've seen it elsewhere as
well) so I feel ok setting it up. I believe that the original intent
was to use telephone style cable with these RJ45 connectors. What
would happen if I used straight through CAT5 ethernet cable?
Electrically I think it'd be ok, and since RS232 isn't a differential
signal the pairs shouldn't have to be matched.

How wrong am I?

:)

Josh
--
A common mistake that people make when trying to design something
completely foolproof is to underestimate the ingenuity of complete
fools.
       -Douglas Adams

2010\05\16@204754 by Ray

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part 1 1464 bytes content-type:text/plain; charset="us-ascii" (decoded quoted-printable)

Josh,
Twisted pairing is important for RS-422 and patch or crossover cable would matter.
But in this case, not as important.
Grouping is nice.
RS-232 is short distance.

So you are right.
Ray


On Sun, 16 May 2010 20:26:56 -0400, Josh Koffman wrote:
{Quote hidden}


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2010\05\16@205116 by Carl Denk

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I'm no expert at this, but I have done the following on cat-5,
connectors haven't been an issue, have used the typical D, and RJ-45:
1: 10' RS-232, 3 wire common, TX, RX, 9600 & 38,400 baud
2: 35' RS-232 3 wire common, TX, RX, 9600 baud
3: RS-485, 2 wire, 9600 baud

All of these have worked without any issues. I would think your chances
are very good for success. :)

On 5/16/2010 8:26 PM, Josh Koffman wrote:
{Quote hidden}

2010\05\16@205743 by William \Chops\ Westfield

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On May 16, 2010, at 5:26 PM, Josh Koffman wrote:

> I'd like to use RJ45 connectors to carry the
> RS232 signal. There is a standard for this (EIA-561, mentioned here
> about 25% of the way down the page, but I've seen it elsewhere as
> well) so I feel ok setting it up. I believe that the original intent
> was to use telephone style cable with these RJ45 connectors. What
> would happen if I used straight through CAT5 ethernet cable?


You should be fine.  I've had people complain that the cisco RJ45  
pinout that we designed ended up putting inappropriate signals on  
"pairs" when used with standard telco closet wiring, but those were  
theoretical objections and I don't think there has ever been an actual  
problem.  (since none of the signals are differential, there aren't  
really "Good" signals to pair up, but presumably it would have been  
nice to have RX and TX each paired up with a GND signal rather than  
one of modem signals or each other.)

Note that the EIA-561 standard for RJ45 wiring is pretty uncommon, as  
far as I know.

BillW

2010\05\16@211111 by Neil Cherry

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On 05/16/2010 08:57 PM, William "Chops" Westfield wrote:
>
> On May 16, 2010, at 5:26 PM, Josh Koffman wrote:
>
>> I'd like to use RJ45 connectors to carry the
>> RS232 signal. There is a standard for this (EIA-561, mentioned here
>> about 25% of the way down the page, but I've seen it elsewhere as
>> well) so I feel ok setting it up. I believe that the original intent
>> was to use telephone style cable with these RJ45 connectors. What
>> would happen if I used straight through CAT5 ethernet cable?
>
>
> You should be fine.  I've had people complain that the cisco RJ45  
> pinout that we designed ended up putting inappropriate signals on  

Cough*DEC*cough ;-)

I have several terminal servers that I use with lots of equipment
(mainly Cisco but my terminal servers are Xyplex). We've extended
the Cisco roll-0ver cables for about 100 feet with out problems
at 9600.

--
Linux Home Automation         Neil Cherry       spam_OUTncherryTakeThisOuTspamlinuxha.com
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http://linuxha.blogspot.com/                    My HA Blog
Author of:            Linux Smart Homes For Dummies

2010\05\17@000230 by William \Chops\ Westfield

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On May 16, 2010, at 6:11 PM, Neil Cherry wrote:

>> You should be fine.  I've had people complain that the cisco RJ45
>> pinout that we designed ended up putting inappropriate signals on
>
> Cough*DEC*cough ;-)

DEC's standard didn't have enough pins, and used weird un-obtainium  
offset RJ plugs.

> I have several terminal servers that I use with lots of equipment
> (mainly Cisco but my terminal servers are Xyplex). We've extended
> the Cisco roll-0ver cables for about 100 feet with out problems
> at 9600.

Yes; rs232 is very forgiving.  In theory, the cisco pinout allows you  
to swap DTE/DCE by switching from a rollover to straight-through  
cable, which I've always liked.  It's other feature is that the  
"usefulness" of signals diminishes as you move outward from center.  
Use the center 4 pins for a 3-wire serial connect, 6 pins to add "hw  
flow control", and all 8 if you want modem control as well.

BillW


2010\05\17@065912 by Olin Lathrop

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Josh Koffman wrote:
> Hi all. I'm working on a board that has a specific use at the moment,
> but I'd like to leave things a bit open for other future uses as well.
> At the moment, there will need to be a connector that talks to a
> device via RS232. It's low speed (9600bps) and short distance (under
> 10 feet, likely under 3 feet). To keep my options open for the future
> (and to aid my design), I'd like to use RJ45 connectors to carry the
> RS232 signal. There is a standard for this (EIA-561, mentioned here
> about 25% of the way down the page, but I've seen it elsewhere as
> well) so I feel ok setting it up. I believe that the original intent
> was to use telephone style cable with these RJ45 connectors. What
> would happen if I used straight through CAT5 ethernet cable?
> Electrically I think it'd be ok, and since RS232 isn't a differential
> signal the pairs shouldn't have to be matched.
>
> How wrong am I?

Seems reasonable to me.  Just make sure that each signal (receive, transmit)
is on its own twisted pair with the other wire of the pair being ground.  In
other words, the minimum RX/TX lines will use up half the CAT5 cable.


********************************************************************
Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products
(978) 742-9014.  Gold level PIC consultants since 2000.

2010\05\17@073049 by Neil Cherry

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On 05/17/2010 12:02 AM, William "Chops" Westfield wrote:
>
> On May 16, 2010, at 6:11 PM, Neil Cherry wrote:
>
>>> You should be fine.  I've had people complain that the cisco RJ45
>>> pinout that we designed ended up putting inappropriate signals on
>>
>> Cough*DEC*cough ;-)
>
> DEC's standard didn't have enough pins, and used weird un-obtainium  
> offset RJ plugs.

Yes that stupid offset drove me nuts. I though I had DEC terminal
servers with all 8 setup in the same manner that Cisco uses? Oh
well, won't be the first time I've been wrong (won't be the last ;-).

{Quote hidden}

Yes, very useful. Many of the other vendors have taken to follow
in step. Simplifies my lfe when it come to cables.

--
Linux Home Automation         Neil Cherry       .....ncherryKILLspamspam@spam@linuxha.com
http://www.linuxha.com/                         Main site
http://linuxha.blogspot.com/                    My HA Blog
Author of:            Linux Smart Homes For Dummies

2010\05\17@074219 by Michael Watterson

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Olin Lathrop wrote:
{Quote hidden}

however many offices use 9,600 or 19,200 RS232 with only one earth wire
and 4 or 6 signals over CAT5 structured wiring, so possibly up to 100m.


This to my mind is most common scheme. The RI pin on DB9 is not
connected. A PC can't generate it. AFAIK only Modems generate it (when
the phone is ringing!) This is also why many OS you can interrupt on
both directions of change on the other Handshake pins but only interrupt
in one direction for RI as it's an event only prior to link establishment

RJ 45 pinouts.ru/SerialPorts/rs232d_pinout.shtml
http://pinouts.ru/SerialPorts/Serial9_pinout.shtml

If a modem is connected over CAT5, then pin 1 is RI on CAT5/RJ45, and
RJ45 pin 1 is connected to pin 9 instead of  pin 6 on DB9

There is an EIA table of distances and speed. It assumes a particular
wire type that is just bundled multi-core with a single overall screen.

Olin's custom twisted pair scheme of ground on each half of each pair is
only needed either for 115k or longer distance.


2010\05\17@080733 by Marechiare

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Josh Koffman wrote:
> What would happen if I used straight through CAT5
> ethernet cable? Electrically I think it'd be ok, and
> since RS232 isn't a differential signal the pairs
> shouldn't have to be matched.
>
> How wrong am I?

You can be badly by introducing ground-loops, it depends on the rest
of your design.

2010\05\17@082949 by Michael Watterson

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Michael Watterson wrote:
{Quote hidden}

Cisco version?
http://pinouts.ru/SerialPortsCables/CiscoConsole9_pinout.shtml

2010\05\17@083019 by Olin Lathrop

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Michael Watterson wrote:
>> Seems reasonable to me.  Just make sure that each signal (receive,
>> transmit) is on its own twisted pair with the other wire of the pair
>> being ground.  In other words, the minimum RX/TX lines will use up
>> half the CAT5 cable.
>>
> however many offices use 9,600 or 19,200 RS232 with only one earth
> wire
> and 4 or 6 signals over CAT5 structured wiring, so possibly up to
> 100m.

RS-232 is pretty forgiving and you can often get away with some sloppiness.
However, that doesn't make it a good idea, nor is a few instances of
something working proof of much.

> Olin's custom twisted pair scheme of ground on each half of each pair
> is only needed either for 115k or longer distance.

I don't know about "custom" since I didn't say anything about pinout.  You
can wire up the connectors to the ends of the CAT5 cable any way you want.
The OP didn't say anything about using pre-made standard ethernet cables,
only "CAT5".  In any case, RS-232 over CAT5 with RJ-45 connectors is pretty
unusual and there isn't much of a standard whether someone wrote something
down or not.

The longer the runs are and the faster the baud rate, the more you need to
clean about things.  It's impossible to come up with a universal limit of
how fast and how far before you need certain precautions.  Ground loops,
external noise, and EMI all make a difference.

Unless the OP needs the extra wires for something else he hasn't mentioned,
I'd go for maximum signal integrity.


********************************************************************
Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products
(978) 742-9014.  Gold level PIC consultants since 2000.

2010\05\17@145902 by Vitaliy

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flavicon
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Michael Watterson wrote:
> Cisco version?
> http://pinouts.ru/SerialPortsCables/CiscoConsole9_pinout.shtml

I remember those from my network installer days, the flat "ribbon" cable and
the DB9 to RJ45 adapters. They can be had dirt cheap (we used to just throw
them away).

Vitaliy

2010\05\17@230636 by William \Chops\ Westfield

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On May 17, 2010, at 11:58 AM, Vitaliy wrote:

> I remember those from my network installer days, the flat "ribbon"  
> cable and
> the DB9 to RJ45 adapters. They can be had dirt cheap (we used to  
> just throw
> them away).

Us too.  Especially the adapters, or the cables with built-in  
adapters, since the most common application in our labs is to plug a  
terminal server port (usually some form of RJ45) into a router/console  
port (also (now) usually RJ45, with a matching pinout.)  For that, you  
just need some combination of flat (rolled) RJ45 cables and RJ45/RJ45  
connectors (always an ODD number of rolls, though...)  I now have a  
big collection, rescued from the dumpers (and I'm considering putting  
them back in the dumpster.  Sigh.)

BillW

2010\05\18@165119 by Josh Koffman

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Hi all,

Thank you all for the great advice. I ended up going with what I'm
going to call "Modified EIA-561". I've only used 4 pins, as following:
Pin    Function
3       Ground
4       Ground
5       Receive
6       Transmit

My thinking behind this is that on a standard ethernet cable this
should result in each data line having a ground line running as its
pair.

Thanks!

Josh
--
A common mistake that people make when trying to design something
completely foolproof is to underestimate the ingenuity of complete
fools.
       -Douglas Adams

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