There have been some questions about cables here recently.  Here are the 
wiring diagrams I've managed to collect in my various setups involving 
Mac<->Mac Serial links, Mac<->NetBSD/mac serial, SLIP and PPP links, and 
Mac<->PC serial links.

Colin,
   You might want to add this to the FAQ



Standard (Apple defined) High-speed Mac Modem cable

			         DIN 8 (MAC/DTE)    	RS-232 (Modem/DCE)
                      ---                    ----
      DTR   HSKo     | 1 |----------------->| 20 |--+  DTR
      CTS   HSKi     | 2 |<-----------------| 5  |  |  CTS
      TxD   TxD-     | 3 |----------------->| 2  |  |  TxD
      GND   GND   +--| 4 |<---------------->| 7  |  |  GND
      RxD   RxD-  |  | 5 |<-----------------| 3  |  |  RxD
      N.A.  TxD+  |  | 6 |---nc        nc---| 6  |  |  DSR
      N.A.  DEAD  |  | 7 |---nc        nc---| 8  |  |  DCD
      N.A.  RxD+  +--| 8 |             nc---| 1  |  |  GND
                      ---                   | 4  |--+  RTS
             Note:                           ----   
                Pins 4 & 8 are hooked together on the MAC side, and also
                connect to pin 7 on the Modem side.  Pins 4 & 20 are 
hooked together
                on the Modem side, and also connect to pin 1 on the MAC 
side.


Industry Standard Full Handshake Null Modem (DB25 to DB-25):
                      ----                    ----
      Frame GND      | 1  |<---------------->| 1  |     Frame GND
      TxD            | 2  |----------------->| 3  |     RxD
      RxD            | 3  |<-----------------| 2  |     TxD
      RTS            | 4  |----------------->| 5  |     CTS
      CTS            | 5  |<-----------------| 4  |     RTS
      DSR            | 6  |----------------->| 8  |--+  DCD
      GND            | 7  |<---------------->| 7  |  |  GND
      DCD         +--| 8  |<-----------------| 6  |  |  DSR
      DTR         +--| 20 |                  | 20 |--+  DTR
                      ----                    ----   

IBM DB-9 to DB-25 Cable:

     Terminal (DTE)     Modem (DCE)
       ----               ----
	TxD  | 3  |------------>| 2  | TxD
	RxD  | 2  |<----------->| 3  | RxD      Note:
	RTS  | 7  |------------>| 4  | RTS         Connect this cable to a Mac
	CTS  | 8  |<------------| 5  | CTS         Modem cable to connect a PC
	DSR  | 6  |<------------| 6  | DSR         DB-9 Communications Port to
	GND  | 5  |<----------->| 7  | GND         a Mac Communications Port.
	DCD  | 1  |<------------| 8  | DCD
	DTR  | 4  |------------>| 20 | DTR
	RNG  | 9  |<------------| 22 | RNG
   		  ----               ----

                                      Mac Serial Printer (non-LocalTalk) 
cable:

      Mac DIN-8 Pins:                            ---                ---
                                           HSKo | 1 |<------------>| 2 | 
HSKi
	     /----###----\                        HSKi | 2 |<------------>| 1 | 
HSKo
	    /     ###     \                       TxD- | 3 |<------------>| 5 | 
RxD-
	   /  [8] [7] [6]  \                      GND  | 4 |<------------>| 4 | 
GND
	   |               |                      RxD- | 5 |<------------>| 3 | 
TxD-
	   | [5]  [4]  [3] |                      TxD+ | 6 |<------------>| 8 | 
RxD+
	   |               |                      N/C  | 7 |<------------>| 7 | 
N/C
    \    [2] [1]    /                      RxD+ | 8 |<------------>| 6 | 
TxD+
	    \--+       +--/                             ---                ---
		    \#|       |#/                       Note:
		     \|--###--|/                           This cable can also be used 
to
		                                           form a Mac-to-Mac 
communications
	Note:				                               				link suitable for 
non-LocalTalk
		   LocalTalk cables only use	            		applications such as 
Zterm-Zterm,
		   pins 3, 5, 6, and 8 connected           or NetBSD Serial, SLIP and 
PPP
		   via electronic coupler (inductor        links.
		   and resistors).