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From: roy@nlm-vax.ARPA (Roy Standing)
Newsgroups: net.micro.mac
Subject: Re: Connecting two MACs for MazeWars
Message-ID: <220@nlm-vax.ARPA>
Date: Thu, 30-May-85 10:50:07 EDT
Article-I.D.: nlm-vax.220
Posted: Thu May 30 10:50:07 1985
Date-Received: Sat, 1-Jun-85 10:56:29 EDT
References: <517@x.UUCP> <206@nlm-vax.ARPA> <147@harvard.ARPA>
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Organization: NLM/LHNCBC, Bethesda, Md.
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> > The serial port is RS422, NOT RS-232 !  If you wire it right,
> > most RS-232 devices won't care.
> > 
> > Pinout:
> > 
> > 1	Ground
> > 2	+5
> > 3	Ground
> > 4	Transmit Data +
> > 5	Transmit Data -
> > 6	+12
> > 7	Incoming handshake
> > 8	Receive Data +
> > 9	Receive Data -
> 
> The second author adds that he converts from RS422 to RS232 as
> follows:
> 
> > MAC Pin	UNIX Pin
> > 1		7
> > 5		2
> > 9		3
> 
> Is it, as I suspect, that the first set of pinouts is actually for
> RS232 and not for the 9-pin plug that's on the back of the MAC?  That
> is, shouldn't I really be connecting mac pin 1 to 1, 5 to 9 and 9 to 5?

The first pinout is really for the Mac's modified RS422 modem port.  THe
suggested MazeWar direct hookup cable simply took advantage of the fact
that most people with Macs have ImageWriters and it is generally easier
to lay ones hands on DB25 connectors than DB9 connectors.  Since the
ImageWriter cable converts from DB9 to DB25 AND RS422 to RS232 the cable
needed to connect the Macs via the ImageWriter cables is 7 straight
through and 2&3 swapped.  If you wanted to make a DB9 to DB9 RS422 cable
then 1 straight through, and 5&9 swapped should do it.  Hope this clears
it up for you.