FYI: Spec for serial null-modem modular adapters

[Rick Richardson]

Bob Drzyzgula writes...
> Hi. This is an FYI not meant for discussion (unless y'all
> want). I'd just been asked for about the fifth time for the
> specifications for some serial null-modem adapters that
> I had made up a few months ago, so I figured I'd write
> it up in a form that can be used as the starting point
> for a requisition or purchase order, and put it where
> people can find it. Rather than post it to all these
> lists, I've put it on my pitiful website at:
> 
> 	http://www.eskimo.com/~bob/serial-spec.txt
> 
> Let me know if you find something wrong or have suggestions
> or problems with it.

This is the usual configuration of RJ-xx to DB-xx adapters we use around
engineering at Digi International.  With this pinout, you just change
the *cable* you are using to connect a DTE to DCE or a DTE to DTE (in
99% of the cases).  We find its far easier to crimp a new RJ on the
end of a cable when you need a null modem than to find a matched set
of adapters.

=============================================================
    DIGI INTERNATONAL STANDARD FOR RS-232 CABLES

RJ-11   RJ-11   RJ-45   RJ-45   Signal  DB-25   DB-9
4-pin   6-pin   8-pin   10-pin  Name    Male    Male

                        1       RI      22      9
                1 bl    2       DCD     8       1
        1 or    2 or    3       RTS     4       7
1 bk    2 bk    3 bk    4       GND     shell   shell
2 rd    3 rd    4 rd    5       TxD     2       3
3 gr    4 gr    5 gr    6       RxD     3       2
4 ye    5 ye    6 ye    7       SG      7       5
        6 bn    7 bn    8       CTS     5       8
                8 gy    9       DTR     20      4
                        10      DSR     6       6

 4-pin: no RTS/CTS flow control, no modem control
 6-pin: RTS/CTS flow control, no modem control
 8-pin: flow control, typical modem control (DTR, DCD)
10-pin: flow control, full modem control (adds DSR, RI)

*  Diagram assumes Digi "altpin" is turned on.

*  Wire colors are "typical" for RJ-45 adapters.  Your
   mileage may vary.  Check your actual adapter!

*  With this pinout, special "null modem" adapters are
   usually unnecessary.  To implement a "null modem" that
   works 99% of the time, simply crimp one RJ connector
   onto the cable the other way, making the *cable*
   "crossover" instead of "straight".  On flat silver
   satin cable, if both plastic RJ connector retaining
   tabs are on the same side of the cable it is a crossover
   cable.  If the plastic retaining tabs are on opposite
   sides of the cable it is a straight-thru cable.
=============================================================

-Rick

-- 
Rick "The Hack" Richardson  rick@dgii.com http://RickRichardson.freeservers.com