* Appendix H: How to make a Serial Cable for your HP48

From: prompt@xs4all.nl (Frank A. Vorstenbosch)

HOW TO MAKE A SERIAL CABLE FOR YOUR HP48
========================================

THE CONNECTOR FOR YOUR HP48

   The connector used in your HP48 is a 4 pin (i.e. male) connector, 
   with pins spaced 2 mm (NOT 0.1") apart.  These connectors are not 
   readily available in stores so you'll have to improvise.  If you 
   happen to have a broken floppy drive or harddisk lying around,
   look inside and see if you can find a connector there that will fit
   the HP48.  Do not use a 0.1" connector, as this will damage the 
   pins in your calculator.
      
   If you can't find a usable connector, then you'll have to make one
   yourself.  For this you need four pins taken from a wire-wrap IC
   socket (available from Radio Shack or some other shop catering for
   DIY electronics).  The smallest IC socket available usually has 8
   pins; so don't worry if you damage a pin while removing it from the
   hard plastic socket.  The pins of the wire-wrap socket are about
   1" long, thereby making soldering them easier than standard sockets.

   Next, solder a 'fork' from thin rigid metal wires, to hold the four
   IC pins spaced at exactly 2 mm while you glue them together with
   superglue.  Glue a plastic 'handle' to the four IC pins to be able
   to remove the connector from the HP48.  You can also indicate the 
   top side of the connector on this handle.

   Note that the hole in the HP48 in which the connector should go
   is not symmetrical; the pins are nearer to the top of the calculator
   than the bottom, and you can use this to make it difficult to insert
   the connector the wrong way up.

   The connector used in the HP48 is a 4 pin male connector, 
   as described above.  However, a connector is readily 
   availible.  Obtain a PC sound card-CD ROM cable.  You can 
   use one of the ends of a sound card-to-CD ROM cable for 
   this connection.- Bob Mcpherson
		     ndku09a@prodigy.com
     
      Connector to plug                          
      in your HP48 (F)    HP48 connector (M)     
      
	   ______               ______
	   |oooo|               |....|           
	   \____/               \____/           
       pin 4   pin 1        pin 1    pin 4


MAKING THE CONNECTIONS

   You can use either a 9 or a 25 pin female sub-D socket for the
   PC-side of the cable.
      
	 9-pin RS232                 25-pin RS232
	connector (F)                connector (F)
      
      pin 5       pin 1    pin 13                     pin 1
	-------------         ---------------------------
	| o o o o o |         | o o o o o o o o o o o o |
	 \ o o o o /           \ o o o o o o o o o o o /
	  ---------             -----------------------
       pin 9     pin 6      pin 25                   pin 14
      
   Use flexible 4-wire cable to connect the four contacts of your HP48
   connector to the PC connector.  Pin 1 of the HP48 should be 
   connected to the metal shield of the RS232 connector.  Usually it
   is not easy to solder this shield; first scratching the shield bare
   (it has some kind of coating) using a screwdriver or a file will 
   help.  If this doesn't work, simply leave pin 1 of the HP48 
   disconnected.  Note that pins 2 and 3 of the RS232 connector must
   be swapped when you use a 25-pin connector.

      HP to PC cable            
      
      HP48 | RS232-9 | RS232-25 
      -----+---------+----------
	1  | shield  |  shield  
	2  |    2    |    3     
	3  |    3    |    2     
	4  |    5    |    7     

   Before connecting the completed cable to your HP48, check for
   short-circuits using an ohmmeter or multimeter set to ohms or 
   "diode test".


HP TO HP CABLE

   If you want to use 9600 bps communication between two HP48s, then
   make two HP48 connectors and simply connect the two, swapping pins
   two and three.

      HP to HP cable

      HP#1 | HP#2
      -----+-----
	1  |  1
	2  |  3
	3  |  2
	4  |  4


WARRANTY, DISCLAIMER ETC.

   Although the serial interface of the HP48 is protected internally,
   it is possible to damage the calculator when a wrong connection is
   made.  I am not responsible for any errors in this file, or for any
   mistakes you may make.