  5.9.  What are the pinouts for the HP48 serial connector?

  Looking at the pins of the HP48 (the following diagram is showing the
  pins on the HP48, as you look at the calculator):


                      _________
                     | o o o o |
                      \_______/
                       ^ ^ ^ ^
                       | | | \------ 4 Signal GND
                       | | \-------- 3 RX (input to the HP48)
                       | \---------- 2 TX (output from the HP48)
                       \------------ 1 SHIELD

       Stated another way:

           HP48                    IBM 9 PIN               IBM 25 PIN
           (From the outside
            edge -> inward)
           SHIELD-------------------  SHIELD----------------  SHIELD
           TX (Output)<-------------2 RX (Input)------------3 RX (Input)
           RX (Input)-------------->3 TX (Output)---------->2 TX (Output)
           SGND---------------------5 GND-------------------7 GND


  This information is also on page 27-7 of the G/GX manual.




  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.


          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 con-
     nected 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.

