12 Apr
2008
12 Apr
'08
6:51 a.m.
On Friday 11 April 2008 23:34, Ethan Dicks wrote:
(Snip)
You might check the pins before randomly rewiring them...
I had intended to, if I go so far as to dig into this thing.
They were sold as "kits" with no pins
inserted, and a prewired RJ45
connector. You inserted the pins into the DB25 and clipped the thing
together.
Some of those connector shells can be opened easier, some are pretty
much necessary to destroy to open it. If I can get it open, I also have
the tool to remove those pins, if necessary. :-) For RJ-45s, the most common arrangement I've seen
is the one presently used
by Cisco - the center two conductors on the cable are both ground, then
flanked by TxD and RxD, then flanked by handshaking lines. Most of the gear
I've seen lately that uses RJ-45s for serial, though, stops with the inner 4
pins.
One handy thing about this interconnection scheme is that you don't
_need_ to change the shells for null modems (though you can). You
can flip one end of an RJ-45 cable (making it unsuitable for Ethernet
use) to make the cable a null modem - the signals are arranged in a
"paired" fashion to make that work.
Yup.
In practice, the flat cables that Cisco ships are
assembled inverted
compared to "Ethernet" cables, so it matters what you grab when you
link up two devices.
Is that the same as a "crossover" cable for LAN use or different? I've not
really looked at the wiring of those things much.
OTOH, I rarely use the RJ-45 scheme with DB25
connections, since the
shells are rarer, in my experience, compared to DE9 shells (which are
*quite* common in the Cisco world). At home, for DB25 stuff, I tend
to use my boxes and boxes of RJ-11 stuff, unless I have a connection
that needs "proper" hardware handshaking - then I usually bust out a
"real" cable.
Thanks for the info, I have no experience with Cisco stuff and wasn't aware
that these were that common.
--
Member of the toughest, meanest, deadliest, most unrelenting -- and
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