Ref: 19140011
Title: Correct Pinout of Crossover Cable for 3Station/2E Printer Spooler
date: 9/28/90

Copyright 3Com Corporation, 1991.  All rights reserved.

When using the 3Station/2E printer spooler, the pinout of the crossover
cable MUST be exactly as described in the third case below.  Other crossover
cables with slight differences cause many problems.

Correct cable:

                   Server               Printer

                FG  1-----------------------1  FG
               TXD  2-----------------------3  RXD
               RXD  3-----------------------2  TXD
               RTS  4-----------------------5  CTS
               CTS  5-----------------------4  RTS
                SG  7-----------------------7  SG
               DSR  6--+-------------------20  DTR
               DCD  8--+
                                         +--6  DSR
               DTR  20-------------------+--8  DCD

The important connection is the cross between 4 and 5, which assures
exchange of CTS/RTS signals, since DTR Flow CTRL is assured by the cross
between 6,8 local with 20 on the other side.

This cable works perfectly as a null modem cable with 3+Open Internet.

If you are using the 3Station/2E printer spooler and an Apple Laserwriter
NTX II Postscript printer, make sure the switch settings on the printer are
as follows:

1   2   3   4   5   6
D   D   U   U   D   D


Following are two examples of similar, but INCORRECT, crossover cables.  Do
NOT use these cables with the 3STation/2E Despooler.

BAD Example #1:  A null modem box bought from MISCO (model 1024)

                   Server               Printer

                FG  1-----------------------1  FG
               TXD  2-----------------------3  RXD
               RXD  3-----------------------2  TXD
               RTS  4--+                 +--4  RTS
               CTS  5--+                 +--5  CTS
                SG  7-----------------------7  SG
               DSR  6--+-------------------20  DTR
               DCD  8--+
                                         +--6  DSR
               DTR  20-------------------+--8  DCD

This cable is wrong, since pin 4 with pin 5 has no sense.

BAD Example #2:

                   Server               Printer

                FG  1-----------------------1  FG
               TXD  2-----------------------3  RXD
               RXD  3-----------------------2  TXD
               SG   7-----------------------7  SG
               DCD  20-------------------+--5  CTS
                                         +- 6  DSR

In this case the problem arises from the lack of symmetry between the
two ends of the cable, since the 3Station probably requires pin 4,5
activity, but the 3Server does not.

