Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!usc!elroy.jpl.nasa.gov!ames!orion.arc.nasa.gov!ogawa
From: ogawa@orion.arc.nasa.gov (Arthur Ogawa)
Newsgroups: comp.sys.mac.misc
Subject: Re: Wiring for hayes modem w/handshaking
Message-ID: <1991Mar24.082806.14851@news.arc.nasa.gov>
Date: 24 Mar 91 08:28:06 GMT
References: <27EB1B0B.3468@ics.uci.edu>
Sender: usenet@news.arc.nasa.gov (USENET Administration)
Organization: NASA Ames Research Center, Moffett Field, CA
Lines: 46
Bcc: ogawa
Cc: aciemian@ics.uci.edu (Alan Ciemian)

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.

For your reference, the above pinout is _not_ the same as that provided
with the Prometheus ProModem I recently purchased. The latter does _not_
jumper modem pins 4 and 20 together (effectively doing CTS=DTR), rather
it jumpers modem pins 6 and 20 together (DSR=DTR). This cable also
connects modem pin 8 to Mac pin 7, providing the Mac with the DCD (Carrier
Detect) signal. Note that my documentation fails to state the fact that
Mac pins 4 and 8 are jumpered together (necessary to anchor Rd+, I think).

I also have a Hayes brand cable in service, but since I am using it 
for this connection, I can't ring it down :-). 

Net mavens have told me that the Mac is not able to support all four
hardware handshaking signals simultaneously (those signals are RTS/CTS
(Ready To Send/Clear To Send) and DSR/DTR (Data Set Ready/Data
Terminal Ready). The pinout of the ProModem supports RTS/CTS and klooches DSR/DTR.

The pinout given by Cieman has a different klooch, namely the modem
sees (via its DTR input) that, whenever it asserts its RTS output, the
Data Terminal (the Mac) is ready.

Interestingly enough, the NeXT's serial port is RS-423, rather than
RS-422, as in the Mac. The former supports the four independent handshaking
signals.

Please email me if you have any corrections to these data. I am certain of
the characteristics of the cable, and the assignment of signal names at
the modem end of the cable, but a little uncertain of my interpretation
of the signals' meanings and the assignment of signal names at the Mac end.
Arthur Ogawa        Internet: ogawa@orion.arc.nasa.gov  Ph: 1/415/691-1126
TeX consultant      AppleLink: ogawa                    FAX:1/415/962-1969