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Re: Serial Connection

Stephen Powell put forth on 3/27/2011 1:41 PM:

> That's true.  But a properly-wired cross-over cable or null modem
> not only crosses over TD and RD but also crosses over DTR and DSR
> and also crosses over RTS and CTS.  Ground, of course, is wired
> to Ground.  CD is normally tied to DSR on the same side of the
> interface (on both sides).  RI is usually left unconnected.

For attaching a terminal all you need to connect are pins 2, 3, and 7 on
a DB25, or 2, 3, and 5 on a DB9.  Reverse 2,3 on one end of each cable
to get your x-over.  All the other pins are for modems only and are not
used for terminal connections.  Serial printers only need 2, 3, 7 as well.

At a previous job about 13 years ago I made so damn many of these serial
x-over cables, daily, that "2, 3, 7" intruded on my dreams...

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.  We'd drop an ethernet->serial terminal server in
each building and then run our custom RJ45 to DB25 cables to the
terminals.  The terminal servers had RJ45 jacks for density.  We used 16
and 48 port models.  Can't recall the brand, been too long (thank God).


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