High Speed Hardware Handshake Cable
-----------------------------------

There is a difference between a normal Modem cabel (such as the one
Apple sells) and a high speed hardware-handshake modem cable.  Hardware
handschake allows the modem and the computer to talk to each other
without having to clog up the data line.  This has two advantages.

 1) It is faster, usually throughput is increased by about 10%
 2) It makes it easier to set the data-rate between modem and computer
 higher than the rate between modem and the far modem.  This is
 necessary for proper operation of data correction and compression
 protokolls such as MNP and V.42/V.42bis.

Some modems even require you to have a hardware handshake cable for
proper operation.

There is one disadvantage.  Because there are only 8 pins on the Mac
serial port one of the signals gets lost.  This is DTR (Data Terminal
Ready) this tells the modem whether a terminal program is running on your
Mac.  You can tell the modem to ignore this signal.


Hardware Handschake Modem Cable:
Mac     Modem
Din 8   DB 25
-----   -----
1       4       used for RTS (you lose DTR, sorry no way around this)
2       5       used for CTS
3       2       TD
4       7       Ground
5       3       RD
6       NC
7       8       Carrier detect
8       7

Connect Mac pins 8 & 4 together, to tell the Apple serial port (RS-432)
to run in the standard RS-232 mode.

Pin 7 (GPi, general purpose pin) is usually used for Carrier Detect.
Carrier Detect tells the Mac that the modem is connected to anoter
modem. Note that Pin 7 (GPi) is available only on the better Macs (not
on the Plus, Classics and LC).

If you already have a standard modem cable you will probably only have
to rewire pin 1 (thats usually whats different). 

Tell the modem to ignore DTR (often on dip switch 1).  You need software
capable of hardware handshaking, of course.

1991 by Duncan McNutt, Rhein-Main Macintosh BBS [FRG-06101-41471] (2:243/100)