Path: utzoo!mnetor!uunet!lll-winken!lll-lcc!ames!mailrus!tut.cis.ohio-state.edu!bgsuvax!denbeste
From: denbeste@bgsuvax.UUCP (William C. DenBesten)
Newsgroups: comp.sys.apple
Subject: Re: GS modem port
Message-ID: <1956@bgsuvax.UUCP>
Date: 22 Apr 88 14:23:42 GMT
References: <8804201709.AA06818@wpi.local>
Organization: Bowling Green State University B.G., Oh.
Lines: 32

> So what is the correspondence to a RS232 DB25 connector?

If you can find a gs (or Mac +) to ImageWriter ONE cable, you have the
cable that you need.

Mini    Name    	Imagewriter I
Din-8           	(db25)
1       HSKo --> DSR	6
2       HSKi <-- DTR	20
3       TxD- --> RxD	3
4       GND   =  GND	7,8 (sGND,DCD)
5       RxD- <-- TxD	2
6       Txd+  
7       n.c.         
8       Rxd+  =  GND	7		ground to simulate RS232

Note: I have not actually tried this.  I don't build cables with the
mini din 8 connectors myself.  They are too small to solder easily.

It turns out that apple uses RS422 serial protocol, not RS232 serial
protocol.  RS422 can be made to emulate RS232 by grounding the
positive receiver and leaving the positive transmitter disconnected.
See Inside Macintosh, volume 3 chapter 2 for more complete details.  I
suspect that the GS Hardware reference manual would cover this also,
but the gs is my home toy, not my work toy.

I am not interested in debating RS422 vs RS232, so don't flame apple's choice.

--
          William C. DenBesten |       denbeste@bgsu.edu
      Dept of Computer Science | CSNET denbeste%andy.bgsu.edu@relay.cs.net
Bowling Green State University | UUCP  ...!cbosgd!osu-cis!bgsuvax!denbeste
  Bowling Green, OH 43403-0214 |