Path: utzoo!utgpu!water!watmath!clyde!rutgers!ucla-cs!cit-vax!elroy!ames!pasteur!ucbvax!MITRE-BEDFORD.ARPA!jhs
From: jhs@MITRE-BEDFORD.ARPA
Newsgroups: comp.sys.atari.8bit
Subject: Linking two computers
Message-ID: <8802191655.AA26182@mitre-bedford.ARPA>
Date: 19 Feb 88 16:55:42 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
Lines: 52

>   I would like to be able to hook up two atari computers for interactive
>   games, etc. that require that you do not see the screen of the other
>   person.
     
>   My brother and I both have Atari 800XL's with parallel ports.  I was
>   wondering if I could buy a parallel-to-parallel cord to use for data
>   transmissions, (for a game of battleship, for example).
Just what port are you referring to by "parallel port"?  Do you have an 850
interface with Centronics printer port or are you referring to the joystick
ports or to the 50-pin bus connector on the back of the 800XL?
Actually, in only one of these cases is there much hope of doing what you ask
with just a "cord".  That is the case of the joystick ports.  I think you
could in fact wire them up with a simple cord and then program them to talk
back and forth.  Of course then you would have no place to plug in the
joysticks, so you would wind up having to do something more complicated than
just a "cord".

I don't think there is any way to program the Centronics ports to accept
inputs, so the 850 approach would require using a serial port at each 850,
which actually is another possibility.

The 50-pin parallel bus connector on the back of the 800XL is hardly a
"parallel port".  If you tied two of these together, I think all that would
happen is both computers would crash because their address lines would
conflict.  You could do almost anything your heart desires with this "port"
but you would have to design an interface from the internal CPU bus (which is
what is on this connector) to the external gadget.  I.e. it's not a question
of a "cord".

>   I have knowledge of machine language, VBI's and DLI's.  I have the
>   technical reference manual, but I find it hard to understand sometimes,
>   especially I/O, since I really don't have the time for it.  I am hoping
>   for a Co-op job this spring and summer, so I'll be in the position that I
>   want to be: working with computers, but still free enough to use my time
>   as I want to (No finals).
I would hate to discourage you from undertaking your project, but from the
tone of your question I get the impression that you may not have much idea
of how much hardware design is involved.  Tackling the project would
undoubtedly teach you a lot about computers, but don't underestimate the
effort involved.

And, finally, a comment that I wish I could go back and tell myself when I
was your age:  Don't think you will have more time to do this project at
any future time in your life.  You almost certainly WILL NOT.  You will just
get busier and busier, at least until you retire at age 65.  The best thing
you could possibly do with your life is to BELIEVE THESE WORDS, think about
their implications, and then figure out how to take this awful news into
account in planning how to live your life right now.  More likely, you will
think I am being silly and will only realize the truth of what I have said
when you are about 40 or 50.  Good luck, either way.

-John Sangster, jhs@mitre-bedford.arpa