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Re: Serial Connection -- shielding

Le 28/03/11 10:30, Russell L. Harris a écrit :
* Stan Hoeppner<stan@hardwarefreak.com>  [110328 06:24]:
Moczik Gabor put forth on 3/28/2011 12:01 AM:
Stan Hoeppner wrote:
We bought DB25 plugs in bags of 100, and used spooled CAT5 as the noise
rejection is many times that of CAT3, allowing greater distances across
sprawling warehouses.
RS-232 uses single-ended signaling and requires shielded cable, twisted
pair doesn't help either.
Shielding provides immunity (not always perfect) against
radio-frequency interference.  But shielding (aside from an enclosure
or conduit of iron or steel) provides no immunity against magnetic

If an RS-232 cable does not run near electric motors or switchgear, or
make a long run parallel to power cables, and if radio-frequency
interference is not a problem, then CAT5, CAT3, or even multiple
strands of lamp cord may be satisfactory, without a shield.  In fact,
lamp cord -- typically 18 AWG stranded copper -- should allow longer
runs, because of its much lower resistance (and thus, lower signal
attenuation).  And, at some point, capacitance of the circuit can
become a problem, because it limits the usable data rate.


I think that the discussion diverted somehow from my original question.

My problem was  the following :
Two identical servers Z0 & Z1 and a null modem cable. ttyS0 on Z0 connected to ttyS1 on Z1.
on ttyS0 on Z0 I have a getty listening for incoming connections.
on ttyS1 on Z1 I launch a minicom toward ttyS0 on Z0 and I login normally.

Now When I try to do the inverse :
Kill getty on ttyS0 on Z0 and remove it from inittab. Set getty to listen to ttyS1 on Z1. Launch minicom on ttyS0 on Z0 toward ttyS1 on Z1.

I can't login all I see is garbage. All the serial parameters are the same on both sides. I thought that logically this setup have to work since I am using the same setup just changing which port on which server.

I am trying to do this for a Datacenter with hundreds of servers. This way I can connect two servers together with just one serial cable.

Does it have something to do with the ttyS0 port? is it a software problem?

Do you have any ideas ? (Apart from theoretical discussions about all the standards)

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