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Article #8 (419 is last):
Newsgroups: freenet.sci.comp.atari.questions
From: ae302
Subject: PARALLEL BUS
Date: Sun Jul 30 08:52:50 1989


NEED HELP WITH INTERFACING TO MY 130XE. 
I HAVE BEEN READING MAPPING THE ATARIAND HAVE COME UPON
REFERENCES TO A POLLING OF THE PARALLEL BUS BY THE OS AT COLD
START. WHAT IS THE POLL LOOKING FOR? A HIGH AT PIN 1(EXSEL)?
ALSO; IT MENTIONS THAT IT PLACES A HANDLER IN THE DEVICE
HANDLER TABLES, WHAT IS THE DEVICE SPECIFICATION(I.E.; D:,R:...)?
LAST ON THIS: WHERE CAN I FIND MORE INFO ON THE BUS?
MAPPING THE ATARI MENTIONS A 4 PART SERIES ON THIS IN ANTIC:THESE I
HAVE READ, BUT WANT MORE SPECIFIC INFO FOR THE 130XE.
ALSO INDIRECTLY RELATED QUESTION:
HAS THE OS FOR THE XE MACHINES BEEN RELEASED IN PRINT?
I HAVE THE OLD OS LISTING,(800 VERSION), BUT IT IS NOT
REAL USEFULL FOR THE XE'S.

                THANKS
                PETE HALLER ae302

** Answered by JOHN SUCHY (aa271) on Sun Dec  6 14:17:25 1987 **

     You don't say what you want to
do with the parallel port.  So I will
answer first your stated question as
well as I can, then what I hope is
your actual need.
     When first turned on, the 8-bit
Atari computer checks several things,
in order:
     the function keys (START, SELECT,
                   and OPTION)
     the SIO port for DOS
     the SIO port for an R: handler
                   (if no DOS), and
     the parallel port.
I believe that all it does for the
parallel port is try to talk to it
by turning on parallel port access
(see D100-D1FF and D800-DFFF) to see
if there is anything there to be used.
Any device that uses the parallel
port must include a custom handler
and may use any NON-STANDARD label.
The exception to this is ICD's MULTI
I/O Board which loads in a Dn:
handler to mimick a disk drive.  The
point is, if you want to create a
parallel port device, you have to
write your own handler.
     As to the XL/XE OS (Operating
System, for those who don't know), it
has not been directly released.  Bits
and pieces are available in "Mapping
the Atari", the magazines, etc.  You
could also try your only gueranteed
complete resource:  Dis-assemble the
OS--IN YOUR OWN COMPUTER!  Both
user groups have dis-assemblers for
members' use.  The best is probably
Ian Carlstrom's Turbo Dis-assembler
(CACE).
     Now, let me speculate that what
you really want is some way to either
control something with your computer
or to sense real-world information.
Several people have written articles
on how to do this using the joystickN
port(s).  It is also possible to
simply reserve one or more memory
locations, "steal" them from memory,
then just read and/or write to those
locations without worrying about all
the fancy handlers and other
considerations.  It just happens that
I wrote an article on this for the
December issue of the CACE newsletter.
Good luck on your project.

                     Your Co-sysop
                     John E. Suchy
                     aa271
      Thanks for asking.


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