Playing With a Soldering Iron

Cable to connect LaserWriter and PC

by Masayo Arai

Hi, fellow TPC members!

I like playing with PCs, but not by playing PC games. My PC at home, whose name is Beauty, is used almost entirely for experiments.

I do not do so many hardware engineering experiments, but I have enough curiosity using a tester and a soldering iron to fix cables and adapters to experiment with how PCs and peripheral devices work. I also like to edit ini files, system files, hidden files, and read only files to experiment with how application software works. In many cases my hypothesis or expectations are wrong and experiments fail, but it's more fun (I never think about things deeply). This is the way I'm playing with my PC.

This time, I'm going to talk a bit about serial cables. Serial cables — there are too many varieties of pin connections, shapes of connectors, and their combination. The differences come from which PC models are used and for which type of serial connection they are used. How they are called is also very curious; very generally they are called serial cables, or RS-232C cables, but usually from the types of pin connection, they are called normal, modem, straight, cross, null, or all-pin connected. It's confusing enough...and fun.

In this AJ issue, I'll introduce the pin connection for PCs and the Apple LaserWriter from my pin connection library. I've been keeping all my experiment notes for years. I turned the pages of my Volume 1 PC notebook (I have 2 volumes of paper notebooks and one electronic text file to keep records of all my experiments).

According to the notebook (that was 1993), I was trying to buy a cable to connect an IBM compatible PC to a second-hand Apple LaserWriter Plus. The cable was not easy to find, so I got pin connection information from one of my friends and made a cable. The pin connection is special. It is not the standard RS-232C cable to connect PCs to peripheral equipment.

Later on, I used the cable for a LaserWriter II NT, and it worked well. I guess this cable works for all LaserWriter series, though I've had no chance to try for all the product line.

If you own a LaserWriter, you can try to make the cable as described in the following. Do not forget to change the LaserWriter mode from Apple Talk to RS-232C. Usually a LaserWriter has some dip switches (very inconvenient to change) or other shape of switch to change the interface mode. You will also use the initialize switch (also sometimes it's needed to move up or down an inconvenient dip switch) if the printer is also connected to Apple Talk.

Cable 1: Apple LaserWriter to IBM PC 
 
Laser Writer end 	      PC end            
                       	RS-232C 
D-sub                   D-sub 
25-pin                  9-pin       (25-pin) 
Male                    Female 
 
Pin # 
 
4 ------------------    1           (8) 
5 ------------------    1           (8) 
2 ------------------    2           (3) 
3 ------------------    3           (2) 
6 ------------------    4           (20) 
7 ------------------    5           (7) 
20 -----------------    6           (6) 
8 ------------------    7           (4) 
8 ------------------    8           (5) 
Shell --------------    Shell       (Shell) 
 
1 (not connected)       9           (1) 
9-19,                               9-19,  
21-25                               21-25 
 

The cable can be made to connect to the 9-pin connector on the PC or the 25-pin connector on the PC. The 9-pin to 25-pin or 25-pin to 9-pin adapters are easily found at PC shops, or you can make them.

Comparing with the standard RS-232C cable that you use to connect your modem to your PC, you can see the difference clearly. Here is the pin connection I checked on the cable connecting my husband's PC and his modem:

Cable 2: Modem to IBM PC 
 
Modem end               PC end 
D-sun 25 pin            D-sub 9 pin 
Male                    Female 
 
Pin # 
 
8 ------------------    1 
3 ------------------    2 
2 ------------------    3 
20------------------    4 
7 ------------------    5 
6  -----------------    6 
4 ------------------    7 
8 ------------------    8 
22------------------    9 
Shell --------------    Shell 
 

The homemade cables are only functionally efficient. But do not forget that unshielded cables emit noise. This causes interference to your nearby TV, radio, and telephone.

This report is just about the fact that I experimented. If someone knows more logical explanations, please let me know. I'm at arai@saed.tmg.nec.co.jp or at the same telephone and fax number as the AJ editor.

See you next time.

[It's mostly Masayo's expertise that keeps The Beast running and me more-or-less sane. — Mike]

© Algorithmica Japonica Copyright Notice: Copyright of material rests with the individual author. Articles may be reprinted by other user groups if the author and original publication are credited. Any other reproduction or use of material herein is prohibited without prior written permission from TPC. The mention of names of products without indication of Trademark or Registered Trademark status in no way implies that these products are not so protected by law.