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From: zben@umd5 (Ben Cranston)
Newsgroups: net.micro.mac
Subject: Re: mac modem cable
Message-ID: <1200@umd5>
Date: Tue, 26-Aug-86 20:14:06 EDT
Article-I.D.: umd5.1200
Posted: Tue Aug 26 20:14:06 1986
Date-Received: Wed, 27-Aug-86 10:41:35 EDT
References: <1150@hou2h.UUCP>
Reply-To: zben@umd5.umd.edu (Ben Cranston)
Organization: University of Maryland, College Park
Lines: 45
Summary: Two cables that seem to work

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 the
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...
-- 
                    umd5.UUCP    <= {seismo!umcp-cs,ihnp4!rlgvax}!cvl!umd5!zben
Ben Cranston zben @ umd2.UMD.EDU    Kingdom of Merryland Sperrows 1100/92
                    umd2.BITNET     "via HASP with RSCS"