* Another document on top of the myriad in the world wide web about *
*                                                                   *
*                   HARDWARE HANDSHAKING CABLE                      *
*                                                                   *
*  to connect a Macintosh and a DCE (data communication equipment)  *

Tuomas Rosberg 1999-10-17 Haemeenlinna, Finland

The following cable is working between Macintosh serial port and 
DB-9-pin serial port in ISDN adapter Telewell ISDN TA128A. 
Hardware handshaking is recommended for DTE-DCE rates > 9600 bps.
The cable is not qualified in any way. Use at your own risk.

The ISDN adapter is cheap, works with older Macs, and is operated 
with AT-commands. The overpriced "Mac adapter" the manufacturer 
recommeds is not needed with this self-made cable. More info about 
the ISDN adapter: <http://www.telewell.com>

Parts of this information are collected from Apple Technical Info 
Library Archives and other sources in www. Sorry about lacking 
references! For more info read Brian's Mac serial summary at 
<http://www.inxpress.net/~bcole/mac/mac_serial_port_summary.txt>

There are two sorts of serial devices, DTE (data terminal equipment)
and DCE (data communication equipment). All microcomputers including 
Macs and all serial printers are DTE:s. All modems are DCE:s. I do
not know which is the case with GSM cellular phones with serial
interfaces.

PC and printer serial interfaces follow loosely the IEEE standard 
RS-232, while Mac (and NeXT and whatelse) and Mac accessories RS-422.
The newer RS-422 is compatible with the older PC serial interface with
some minor exeptions. This means serial accessories for PC work with 
Mac (provided driver software exists). 

Mac serial ports: Mac Plus (1986) was the 1st with mini-DIN-8 connectors.
The AV and PowerPC Macs 1994 - 1998 had a modified, faster serial ports 
called Geoports, wich accept this cable as well. Note: the newest Macs 
(from iMac and Blue & White G3 on) have only Universal Serial Ports 
(USB), which do not accept this cable, and need USB accessories.

_____________________________________________________________________

1. The connectors:
 
Pin numbers of the DE-9 male connector in the back of the ISDN adapter

   -----------
  \ 5 4 3 2 1 /
   \ 9 8 7 6 /
     -------

Pin numbers of the mini-DIN-8 female connector in the back of Macintosh

        _ _
             
     / 8 7 6 \
    | 5   4 3 |
     \  2 1  /
        ___ 
       
_____________________________________________________________________

2. The subset of lines and corresponding pin numbers:

RS-232 with DE-9-pin connector:                     
line description     abbreviation pin # 
----------------------------------------
chassis ground       gnd          shield
Data Carrier Detect  DCD          1
Receive Data         RD           2
Transmit Data        TD           3
Data Terminal Ready  DTR          4
Signal Ground        SG           5
Data Set Ready       DSR          6
Request To Send      RTS          7
Clear To Send        CTS          8
Ring Indicator       RI           9


RS-422 with mini-DIN-8-pin connector:
line description    abbreviation  pin # 
----------------------------------------
chassis ground       gnd          shield 
Handshake Out        HSKo         1
Handshake In*        HSKi         2
Transmit Data negat. TxD-         3
Signal Ground        SG           4
Receive Data negat.  RxD-         5
Transmit Data posit. TxD+         6
General Purpose In   GPi          7
Receive Data posit.  RxD+         8

*HSKi can be used for external clock, too.
_____________________________________________________________________

3. Generic Macintosh-to-modem-hardware-handshaking cable:

Mac                          DCE

gnd  ----------------------- gnd
HSKo  ---------------------> DTR, RTS
HSKi  <--------------------- CTS
TxD  ----------------------> TD
SG, RxD+  ------------------ SG
RxD-  <--------------------- RD
GPi <----------------------- DCD

Use preferably shielded cable. The other pins are left unconnected.
Configure your software to use RTS-CTS-handshaking 
(= hardware handshaking).