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From: zben@umd5 (Ben Cranston)
Newsgroups: net.micro.mac
Subject: Re: Modems on a Mac Plus
Message-ID: <1296@umd5>
Date: Fri, 17-Oct-86 14:42:09 EDT
Article-I.D.: umd5.1296
Posted: Fri Oct 17 14:42:09 1986
Date-Received: Sat, 18-Oct-86 00:49:38 EDT
References: <1144@druhi.UUCP>
Reply-To: zben@umd5.umd.edu (Ben Cranston)
Organization: University of Maryland, College Park
Lines: 90
Summary: Here are some cable pinouts and suggestions

In article <1144@druhi.UUCP> cosmos@druhi.UUCP (Ron Guest) writes:

> Has anyone connected a non-Apple modem to the modem port of a Macintosh
> Plus?  I would imagine someone has....  What connections did you use to make
> it work?  Did you have any trouble?

I couldn't find the 8 pin Din males anywhere, so I decided to use the
adapter cable that came with the Mac + and got myself some DB9 males
and made up these two cables:

For connecting Mac to Modem or other DCE-type Female:

  DB9 Male                              DB25 MALE

       GROUND 3 O------+----------------O 7  GROUND
  XMIT DATA + 4 O-x    )
  XMIT DATA - 5 O------)----------------O 2  XMIT DATA
HANDSHAKE OUT 6 O---+--)----------------O 20 DATA TERMINAL READY
HANDSHAKE  IN 7 O---+  |            +---O 4  REQUEST TO SEND
  RECV DATA + 8 O------+            +---O 5  CLEAR TO SEND
  RECV DATA - 9 O-----------------------O 3  RECV DATA

This works with our three-wire Gandalf network inhouse and with a Courier
modem at home.  The Mac is the new RS-422 (?) balanced protocol, and the
old RS-232 had inverted data, so the DATA - goes across and the DATA +
gets grounded to complete the circuit.  Do NOT ground XMIT + !

For connecting Mac to Terminal or other DTE-type Male:

  DB9 Male                              DB25 FEMALE
       GROUND 3 O------+----------------O 7  GROUND
  XMIT DATA + 4 O-x    |
  XMIT DATA - 5 O------)----------------O 3  RECV DATA
HANDSHAKE OUT 6 O-x    |
HANDSHAKE  IN 7 O------)----------------O 20 DTR
  RECV DATA + 8 O------+
  RECV DATA - 9 O-----------------------O 2  XMIT DATA

This works with an H19 at home and a Volker Craig 4404 at work.  If your
device is persnickety it might want Carrier Detect on pin 8, if so then
connect 8 to 20 at the DB25 end (so DTR drives it).  One might also have
to connect pins 4 and 5 (RTS-CTS) together at the DB25 end to make some
devices happy.

Other than that, get a breakout box and read the specs, and if it does
not work then don't leave it connected long enough to get hot...

------------------------------------------------------------
Several months later:
------------------------------------------------------------

On old MACs the DTR line was held high by hardware.  On the Mac Plus there
is a driver for the DTR line.  SOME of the older terminal programs don't
have the code to drive DTR high, and SOME modems require DTR.  If at ALL
possible, set your modem up to IGNORE DTR and stay on all the time.  This
fixes a multitude of problems...

DIN 8 connectors are available.  They're just a @#$%^&*( to work with.  It
takes me half a day to make one cable, and I ruin 40% of the connectors I
try (and at $3.75 a connector that ain't cheap).  The only way I have found
to do this is to hand strip a few inches of Slit-N-Wrap wire, CAREFULLY
solder that to the connector pins (and HEAT SINK the pin too), then solder
the other end of the Slit-N-Wrap wire to the cable proper.  Really tedious.

Macintosh Plus to modem (or other DCE device):

  DIN 8 Male                            DB25 MALE

       GROUND 4 O--+--------------------O 7  GROUND
  RECV DATA + 8 O--+
  XMIT DATA - 3 O-----------------------O 2  TD
HANDSHAKE OUT 1 O--+
HANDSHAKE  IN 2 O--+--------------------O 20 DTR
  RECV DATA - 5 O-----------------------O 3  RD

Macintosh Plus to terminal (or other DTE device):

  DIN 8 Male                            DB25 FEMALE

       GROUND 4 O--+--------------------O 7 GROUND
  RECV DATA + 8 O--+
  XMIT DATA - 3 O-----------------------O 3  RD
HANDSHAKE  IN 2 O-----------------------O 20 DTR
  RECV DATA - 5 O-----------------------O 2  TD

"A boat anchor doesn't have a BIOS..."  :-)
-- 
                    umd5.UUCP    <= {seismo!umcp-cs,ihnp4!rlgvax}!cvl!umd5!zben
Ben Cranston zben @ umd2.UMD.EDU    Kingdom of Merryland Sperrows 1100/92
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