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From: robin@uhunix1.uhcc.Hawaii.Edu (Robin Amano)
Newsgroups: comp.sys.ibm.pc.hardware
Subject: Re: null modem cable
Message-ID: <11224@uhccux.uhcc.Hawaii.Edu>
Date: 31 Jan 91 19:17:28 GMT
References: <1991Jan27.123115.23732@ericsson.se> <3446@nosc.NOSC.MIL> <11184@uhccux.uhcc.Hawaii.Edu> <1991Jan31.140137.25101@batcomputer.tn.cornell.edu>
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In article <1991Jan31.140137.25101@batcomputer.tn.cornell.edu> pwong@batcomputer.tn.cornell.edu (Patrick Wong) writes:
>
>Just to add confusion to the net.  I opened up a el cheapo "RS232 NULL
>MODEM" sold by CompuAdd and here is what I find:
>
>                2 ------ 3
>                3 ------ 2
>              |-4        4-|
>              |-5        5-|
>                7 ------ 7
>             |-20        20-|
>             |--8        8--|
>             |--6        6--|
>
>Note that there is no interconnection between any of 6,8,20 pins on one
>side to any of the same set of pins on the other side.
>
>Have fun in searching for the ultimate null modem!
>
>Patrick
>pcw@squid.graphics.cornell.edu


This cable will definitely work also.  Although if you are using 
hardware flow control you may have problems, because there is
no control line.  But, if you use xon/xoff it should be fine.
Although a lot of times if the devices are using xon/xoff a
three wire hook up is all that is needed 2,3, & 7.  But, by
all means not all the time.  RS232 is standard in a sense that
you could guess and make it work or in tough situations, if you
have a breakout box you could figure it out, 'cuz not every
manufacturer does it exactly the same.  I remember on a pc
using yterm going to a starmaster(pacx) switch we had to use
the 4-5, 6-8-20 jumpers on the pc end because yterm was looking
for a modem.  When we hooked up a ps/2 to the switch using yterm,
it wouldn't work.  We found that pin 8 was pulling down pin 20,
we snipped off 8 and it worked fine.  So, we use that pinout as
a time saver or if we don't have a manual, because most of the time
it will work.  If it doesn't work, then we'll go in with a breakout
box and modify it a little.

Well, goodluck!     what are we talking about this for anyway?


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  Robin Amano          |  robin@uhunix.uhcc.hawaii.edu
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