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From: koziarz@halibut.nosc.mil (Walter A. Koziarz)
Newsgroups: comp.sys.ibm.pc.hardware
Subject: Re: null modem cable
Message-ID: <3446@nosc.NOSC.MIL>
Date: 28 Jan 91 23:13:14 GMT
References: <8Fy4V2w163w@cybrspc> <3439@nosc.NOSC.MIL> <1991Jan27.123115.23732@ericsson.se>
Sender: nobody@nosc.NOSC.MIL
Organization: Naval Ocean Systems Center, San Diego
Lines: 30

In article <1991Jan27.123115.23732@ericsson.se> etxsral@california.ericsson.se (Lars Nilsson) writes:
>In article <3439@nosc.NOSC.MIL> koziarz@halibut.nosc.mil (Walter A. Koziarz) writes:
>>It's never a good move to try to 'fake-out' hardware handshaking!!!!!  Don't do
>>it!!  Presented below is *the RIGHT way* to make a null modem cable --
>>[1]------chassis GND--------[1]
>>[2]-------------------------[3]
>>[3]-------------------------[2]
>>[4]-------------------------[5]
>>[5]-------------------------[4]
>>[6]------------------------[20]
>>[7]-----signal GND----------[7]
>>[8]-------------------------[8]
>>[20]------------------------[6] 
>>This is the correct wat to make a FULL-HANDSHAKING null modem; throw away
>>ANYTHING that tells you to use the 'other', fake-out connection.
>
>Uhmm.  Your solution seems good except for the pin 8 to pin 8 connection
>,connecting an input to an input doesnt work so good.
>I usually connect pin 8 -- 6 to 20 in the other end.
>/Lars Nilsson


Ah, but I'm *not* connecting an input to an input.  A null modem is used when
'I've got an available DCE port and need to connect a DTE device' or vice
versa.  Examination of pin 8 [DCD] for a DCE device port (female on the
computer) shows it to be an output.  And for a DTE device port; it is an input.
DCE -- printer; DTE -- modem in my context.  I submit that my connection is
indeed correct and valid.

Walt K.