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From: russotto@eng.umd.edu (Matthew T. Russotto)
Newsgroups: comp.sys.mac.misc
Subject: Re: Wiring for hayes modem w/handshaking
Message-ID: <1991Mar24.190944.10956@eng.umd.edu>
Date: 24 Mar 91 19:09:44 GMT
References: <27EB1B0B.3468@ics.uci.edu>
Sender: news@eng.umd.edu (C-News)
Organization: College of Engineering, Maryversity of Uniland, College Park
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In article <27EB1B0B.3468@ics.uci.edu> aciemian@ics.uci.edu (Alan Ciemian) writes:
>A few people have requested that I post the cable wiring for a 
>mac DIN-8 to modem w/handshaking.  Thanks and apologies to 
>Software Ventures.
>
>MAC DIN-8        modem 25 pin
>----------------------------------
>pin 1      to    pin 4 and pin 20
>pin 2      to    pin 5
>pin 3      to    pin 2
>pin 4      to    pin 7
>pin 5      to    pin 3
>
>There is also a jumper from pin 4 to pin 8 on the mac side (or also
>connect mac pin 8 to modem pin 7.
>
>
>To adapt a standard cable at the modem end wire an adapter as follows:
>
>
>mac side    modem side
>-----------------------
>pin 2      to pin 2
>pin 3      to pin 3
>pin 5      to pin 5
>pin 7      to pin 7
>pin 20     to pin 20
>pin 20     to pin 4

This is not a flame, merely a correction:
You don't want pin 20 connected at the modem end at all.  Pin 20 is Data
Terminal Ready, and many modems will not accept commands if it is low,
and will hang up if it is dropped.  Thus, the cable will work fine--- UNTIL
handshaking is used, at which point the mac TRIES to tell the modem not
to send any more, but instead tells it to hang up.  So don't connect pin 20
at all, and set the modem to ignore terminal DTR (usually a dipswitch).

The adaptor cable allows only one-way handshaking from the modem to the mac
if the DTR is not a problem.  To allow two way handshaking with most cables,
pin 8 on the mac side should be connected to pin 5 on the modem side (most
cables are set up so pin 8, carrier detect, goes to handshake in).  Pin 20
(Mac side) should go to pin 4 (modem side) ONLY-- not pin 20 (modem side)

If you like, with the regular cable (not the adaptor), connect pin 7 (mac
end) to pin 8 (modem end), to allow carrier detect on the general-purpose
input (if your software supports it-- most doesn't)
--
Matthew T. Russotto	russotto@eng.umd.edu	russotto@wam.umd.edu
     .sig under construction, like the rest of this campus.