Path: utzoo!attcan!uunet!timbuk!cs.umn.edu!kksys!orbit!pnet51!amadeus
From: amadeus@pnet51.orb.mn.org (Christoper Helget)
Newsgroups: comp.sys.mac.hardware
Subject: Re: Mac Serial Port Pinout
Message-ID: <3273@orbit.cts.com>
Date: 1 Oct 90 13:47:22 GMT
Sender: root@orbit.cts.com
Organization: People-Net [pnet51], Minneapolis, MN.
Lines: 36

The pin #'s for the 8 pin mini-din are correct except that you give the pin
#'s for the cable, the actual ports are just the opposite.  The pinouts are
now graciously given by Apple in the latest Owners Guides as follows:
 
Pin     Signal  Description
1       HSKo            Handshake out
2       HSKi            Handshake in/external clock
3       TXD-            Transmit data -
4       GND             Signal Ground
5       RXD-            Receive data -
6       TXD+            Transmit data +
7       GPi             General Purpose input (for hardware handshaking w/
modems)
8       RXD+            Receive data +
 
The Mac serial port uses the RS-422 format (because it is good for long
distances) so what you want to do for normal RS-232 is to ground the "+" lines
and use the "-" lines as your transmit and receive.  
 
DB-25                           Mini-din 8
Shield --------------------  Shield
2  ------------------------  3
3  ------------------------  5
6  ------------------------  2
8  ------------------------  2
7  ------------------------  4 & 8
20  -----------------------  1
 
This is exactly how the Mac to serial printer cable is wired & I've been using
it with my modem.

(I tried E-mailing you but it was returned undelivered...)

UUCP: {amdahl!bungia, uunet!rosevax, crash}!orbit!pnet51!amadeus
ARPA: crash!orbit!pnet51!amadeus@nosc.mil
INET: amadeus@pnet51.orb.mn.org