12 Apr
2008
12 Apr
'08
5:15 p.m.
On 12/04/2008 14:51, Roy J. Tellason wrote:
Someone else wrote:
> 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.
[ ... ]
> 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.
Ask Google about "YOST", which is where Cisco and Sun copied the scheme.
But be aware that almost every way you could think of to use an RJ45
for serial has been tried by someone -- and if you want a laugh of the
"I don't believe it" sort, look up EIA/TIA-561.
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.
No, LAN cables are wired with twisted pairs for 1+2, 7+8, 3+6 and 4+5.
To make an Ethernet crossover, you swap 1+2 with 3+6 but you leave the
others as-is.
--
Pete Peter Turnbull
Network Manager
University of York