Path: utzoo!mnetor!uunet!husc6!bloom-beacon!mit-eddie!uw-beaver!tektronix!reed!kamath
From: kamath@reed.UUCP (Sean Kamath)
Newsgroups: comp.sys.apple
Subject: Re: GS modem port
Message-ID: <9002@reed.UUCP>
Date: 23 Apr 88 23:20:57 GMT
References: <8804201709.AA06818@wpi.local>
Reply-To: kamath@reed.UUCP (Sean Kamath)
Organization: Reed College, Portland OR
Lines: 44

In article <8804201709.AA06818@wpi.local> DSEAH@WPI.BITNET writes:
>A kind soul suggested that the minus was for
>RS422 communications.
>
>So what is the correspondence to a RS232 DB25 connector?
>
>|              Dave Seah --- Worcester Polytechnic Institute                |

Well, you can use rs-422 with rs-252 by only using the minus pins.  Let me
hope I'm right here, but the Mac and GS use the same serial controller, and
are both rs-422, and I recall that this is what we did.  I.e. use -TxD and
-Rxd to got to TxD and RxD on the 232 device, and sig ground to sig ground,
case to case.

>PRINTER and MODEM PORTS
>
>Pin#  Signal descriptions       Pin#  Signal description
>--------------------------------------------------------
>1       Handshake out           5       Receive data minus
>2       Handshake in            6       Transmit data plus
>3       Transmit data minus     7       Goes to DCD input on SCC
>4       Signal ground           8       Receive data plus

so, in more or less "standard" jargon, pin one and two are general hanshake
lines, which go high or low to signal busy. They have no direct equivilant
in rs-232.  Pin 6 and 8 likewise have no equiv. in 232.  Pin 3 and 5 are 232
pins 2 and 3 (or 3 and 2.  THis is the biggest bogus situation I've ever
seen.  Cables should have a switch on them saying "swap 2 and 3".) four is
seven, and I'm not sure what 7 is.  Also, what is SCC? I assume it is Serial
Comunications something, or some such.  If it goes to Data Carrier Detect,
then it probably is high.

Sean Kamath

OK, so this is somewhat confusing.  I have built a cable that goes from
mini-8 to DB25.  But unless I know the whole story, I get a little
confused.  I'm not *possitive* the mac and GS use the *exact* same cabling.
If it does, and poeple want more descriptive text, I'll be glad to do it
right.
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