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From: NEY7@HBUNOS.BITNET
Newsgroups: comp.sys.apple
Subject: Re: RS-422 to RS-232C
Message-ID: <8709281406.aa09789@SMOKE.BRL.ARPA>
Date: Tue, 29-Sep-87 04:06:24 EDT
Article-I.D.: SMOKE.8709281406.aa09789
Posted: Tue Sep 29 04:06:24 1987
Date-Received: Wed, 30-Sep-87 06:39:12 EDT
Sender: usenet@ucbvax.BERKELEY.EDU
Organization: The ARPA Internet
Lines: 56

For Matthias Kapffer's questions:
The wiring for a GS-serial-port and a modem,is as follows:



GS serial port                          Modem

      1....>>...........DTR..............20

      2.................DSR......<<.......6

      3....>>...........TxD...............2

      4.................GND...............7

      5.................RxD......<<.......3

      7.................DCD......<<.......8

1.The arrows mark the direction of the signal (i.e,DTR is output from the
modem into the computer etc,).

2.The numbers for on the GS port column assume the following numbering on the
connector:

        +++#  #+++
     +     #__#    +
    +   8   7   6    +
   +                  +
   +   5   4     3    +
   +                  +
    +     2    1     +
      ###        ###
       +#        #+
           ++++

3.The numbers on the modem column assume the standart DB-25 RS232 connector.

As to 'minimal connection',I don't think there are many modems that would
compromise on DTR.Anyhow,lack of DSR and DCD is usualy more tolerable.

TxD+/TxD- and  RxD+/RxD- is part of the glorious RS 422 concept,and more
accurately,of a method called 'differencial signal'.In this method,for each
of the Receive and Transmit signals,one wire carries the signal just as it
would on RS 232,and a second wire carries the first's inverse polarity.(Thus
the couples xD+/xD-).Now,the receiving device compares the xD+ to it's
inversed partner.If xD+ is higher than xD-,the receiving device reads 'high',
if it's lower,the device reads 'low'.What you get is a speed considerably
higher than on RS 232,and a connection much more emmune to noises.

You'll have to work out the appropriate Control-Panel configuration according
to the modem and software you use.

                                    Yoram Ney
                             Hebrew University,Jerusalem
                                Bitnet:NEY7@HBUNOS