🚀 go-pugleaf

Here's the pin layout for the modem port on the Mac.  This
description is from Cary Lu's book.

1	Cold ground
2	+5 volts
3	Cold ground
4	Transmitted data +
5	Transmitted data -
6	Filtered +12 volts
7	Handshake for printer or carrier detect; also for
	external clock in synchronous communication.
8	Received data +
9	Received data -

	Although power is available on lines 2 and 6, any
	connecting devices should not depend on the power;
	the available current is small and the power is not
	guaranteed in future designs.

I used the following pins in the cable that I use to connect my
Mac to a US Robotics Auto Dial 212A modem.  Note that pin 5 on
the RS-232C side is simply jumpered to pin 20.  This hold DTR
high.  If I don't do this, my modem drops carrier almost instantly.
By the way, I don't pretend to understand any of this.

	  RS-422	  RS-232C
	Mac DB-9	Modem DB-25

	   5		     2
	   9	 	     3
			     5 -+
  	   1		     7  | jumper
	   7		    20 -+

Good luck.

---------------
Bob Paver
MCC
Austin, TX

paver@mcc.arpa