Conference hydra::amiga_v1

3880.0. "HP48SX <--> Amiga" by EUCLID::OWEN (I will not instigate revolution) Wed Jun 27 1990 14:58

Article         2620
From: lishka@uwslh.slh.wisc.edu (Chris Lishka (friend of jabberwockies) )
Subject: HP48sx to Amiga cable: how to build it.
Date: 25 Jun 90 15:48:31 GMT
Organization: Wisconsin State Laboratory of Hygiene
 
I have received too many questions asking how to build an HP48sx/Amiga
serial cable, so I am going to post this out over the net.  Note that
this information can likely be used for building HP48sx cables for
other computers as well.  Much of the information in this article was
distilled from previous postings.  
 
Disclaimer: as always, you use this information at your own risk!  I
will not be held responsible for anyone burning out their Amiga's
serial port or HP48sx, or any other problems that occur.  If you
really want a safe method for connecting your HP48sx to your Amiga,
buy the IBM cable that HP sells (they offer one without the software,
for around $30, I believe). 
 
What motivated me to build my own cable, when I could buy one from HP?
Well, I had some spare rs232 connectors lying around the house, as
well as some cable.  All I needed was to purchase (or make) some sort
of connector for the HP48sx.  In the end, I spent less than a $1 on
parts, as compared to around $30 for the HP cable.  I did put in some
elbow grease, though.
 
The hardest part was trying to make a decent connector for the HP48sx.
Apparently, there is a Molex connector (Molex #22-01-2041 for the
terminal housing, Molex #08-50-0114 for the terminal pins) that fits
the HP48sx port.  However, the only place I could find locally that
had it would have to special order it for me, in quantities of at
least 100 units.  Since I didn't have 100 HP48sx's sitting around ;-),
I decided to fabricate my own connector using some hints printed in a
previous posting. 
 
The rs232 connector should be a standard 23-pin package.  Make sure
you get the correct one (male vs. female) for you computer.
 
Here's how to make female pins that will fit the HP48sx male pines.
Get ahold of four rs232 female pins.  I bought a nine-pin connector
(the kind used for Atari joysticks) at Radio Shack for around a $1; I
then threw away the connector and used the pins from it.  You will
have to squeeze each pin slightly so that it has less space between
the two halves.  This will provide a much better connection to the
HP48sx.  Here are "before" and "after" pictures:
 
		Before				After
 
		 /  \				 /
		|    |	-- squeeze -->		|  \
		 \  /				 \  |
						   /
 
I simply wrapped each pin in electrical tape, and I plug them in
individually.  Another possibility is to use some insulating material
that shrinks when it is contacted by heat instead of electrical tape.
You might want to fashion the pins into a single connector, or pick up
the Molex connector.  I found that the easiest method was simply to
label each individual pin, and plug them in one-at-a-time whenever I
connect my HP48sx to the Amiga.
 
The HP48sx has four pins in its serial port.  I shall number them as
follows: 
                  Top
	   F     E    D    C    B    A      Function key positions
        +-------------------------------+
        |    o o o o                    |   This is looking into the
        |    1 2 3 4                    |   serial port.
	\_______________________________/
                  Bottom 
 
 
The pins functions are as follows (to the best of my knowledge):
 
	Pin	Function		RS232 Equivalent Pin
	===	========		====================
	 1	Chassis Ground		RS232 Pin 1
	 2	Transmitted Data	RS232 Pin 2
	 3	Received Data		RS232 Pin 3
	 4	Signal Ground		RS232 Pin 7
 
As you can see, the HP48sx serial port is simply an RS232 port with
the unnecessary pins left out.  In my opinion, this was a very wise
choice made by HP, for it allows the HP48sx to be connected to
virtually any RS232 device with the correct cable.  HP could have made
this much more complicated with Request/Clear-to-Send and
Data-Set/Terminal-Ready lines; I am very glad that they didn't!
 
The next step is to wire it all up.  Here are the correct pins to wire
up each end.  I am deriving this right now by using an ohm-meter to
test the connections on each end.  I have verified this with past
postings as well.
 
HP48 Purpose		HP48sx		RS232	RS232 Purpose
============		======		=====	=============
Chassis Ground		Pin 1	--->	Pin 1	Chassis Ground
Transmitted Data	Pin 2	--->	Pin 3	Received Data
Received Data		Pin 3	--->	Pin 2	Transmitted Data
Signal Ground		Pin 7	--->	Pin 7	Signal Ground
 
HP48sx pins 1 and 4 are directly wired to their RS232 counterparts.
HP48sx pins 2 and 3 are switched with their RS232 counterparts.  Some
of you may recognize this as the wiring for a "null modem."
 
A quick summary of the steps required:
 
	(1) Purchase a standard rs232 connector of the appropriate
	    for your computer.
 
	(2) Either (a) purchase the Molex connector, or (b) fabricate
	    some female pins from standard rs232 pins.  You may want
	    to form the pins from step (b) into a single connector;
	    make sure each pin is properly insulated if you do!
 
	(3) Wire up the two ends according to the diagrams above.
 
	(4) Voila! Hopefully, you now have a working cable.
 
Once you have it all wired up, choose your favorite communications
program which has the KERMIT tramission protocol built in.  I have
found that both VLT and VT100 work fine.  I typically use 8 bits, no
parity, no XON/XOFF, and 4800 baud on the Amiga end.  The I/O setup
screen on my HP48sx looks like:
 
		    I/O setup menu
		IR/wire:       wire
		ASCII/binary:  binary	(binary *or* ASCII, as appropriate)
		baud:          4800
		parity:        none 0
                checksum type: 1
		translate code:3
 
The reason I use 4800 baud is that there are known bugs associated
with running 9600 in conjunction with the clock display.  If you do
ASCII transfers, the limiting factor in transmission speed is the time
it takes the HP48sx to convert to ASCII, so the difference between
4800 and 9600 baud is negligible.  Also, since I only have 32k, the
difference between 4800 and 9600 baud binary transfers are also
negligible. 
 
Follow the instruction in the HP48sx manual for your particular
transfer needs.  There are too many different types of transfer to
discuss here, and the manual does a good job of explaining the various
aspects involved.
 
Here are some problems I have encountered, with solutions that I have
used: 
 
* When testing your cable, make sure you have IR/wire (in the I/O
setup menu) set to "wire" and not IR!  This caused me a lot of wasted
time one night.
 
* Be careful not to short pins together.  This won't necessarily
damage anaything (at least it hasn't in my setup), but you will get
transmission errors.  The HP48sx is *very* robust when it comes to
shorted pins; I believe that someone from HP stated that shorting pins
would not hurt the HP48sx.  I am not sure if it will hurt the Amiga,
so avoid this problem.  The solution: properly insulate each pin!
 
* My Amiga usually dies (with a software error or screen pyrotechnics,
followed by a GURU) when an error is encountered in the Kermit
transmission.  VT100 tends to be better behaved than VLT in this
respect.  It is likely a problem with VLT not interacting well with my
hardware, because it occurs even when I disable the startup-sequence.
I have spoken with someone at Commodore, and he suspects that it may
be a problem with VLT and chip memory above $C00000 (I have an A2000
with 1 meg chip ram, and no fast ram).  I have never had faulty
transmissions, though; just crashes after errors already occurred.
The solution: grin and bear it for now, and reboot the Amiga if
necessary.  I will likely purchase some fast ram, to see if that fixes
it. 
 
* I have had cases where pin 1 on the cable becomes disconnected from
pin 1 on the HP48sx.  Nothing happened, actually; the transfer went
off without a hitch.  But it is better to keep all pins properly
connected!
 
So that's it!  I hope this provides everyone with enough information
to go out and make their own Amiga cable now.  Remember, you do this
at your own risk!  Buy the HP IBM cable if you are getting queasy at
this point.  My experiences, though, have been fairly good.
 
One request: if anyone else has problems with VLT and the Amiga, could
you send me email?  I would like to figure out what is causing these
crashes. 
 
					.oO Chris Oo.
-- 
Christopher Lishka 608-262-4485  "Dad, don't give in to mob mentality!"
Wisconsin State Lab. of Hygiene                                -- Bart Simpson
   lishka@uwslh.slh.wisc.edu     "I'm not, Son.  I'm jumping on the bandwagon."
   uunet!uwvax!uwslh!lishka                                    -- Homer Simpson