INTRODUCTION
Bill Wilkinson


When I was asked by the editors at COMPUTE! to write this
introduction, I was at first a little hesitant. How does one introduce
what is essentially a map of the significant locations on the Atari other
than by saying "This is a map of..."?   
     And, yet, there is something about this book which makes it more
than "simply a map." After all, if this were "simply" a memory map, I
might "simply" use it to learn that "SSKCTL" is the "serial port
control" and that it is at location $232. But what does that mean? Why
would I want to control the serial port? How would I control it?
     The value of this book, then, lies not so much in the map itself as it
does in the explanations of the various functions and controls and the
implications thereof. Even though I consider myself reasonably
familiar with the Atari (and its ROM-based operating system), I expect
to use this book often.
     Until now, if I needed to use an exotic location somewhere in the
hardware registers, I would have to first locate the proper listing, then
find the right routine within the listing, figure out why and how the
routine was accessing the given register, and finally try to make sure
that there were no other routines that also accessed this same register.
Whew! Now, I will open this book, turn to the right page, find out what
I need to know, and start programming.
     Okay. So much for this introduction. And if you are comfortable
programming your "home" language, the language you know best,
and two or three other languages, you don't need any more from me.
So good luck and bon voyage.

A Common Problem
What? Still with me? Does that mean that you are not comfortable
doing memory mapped access in three or four languages? Well, to tell
the truth, neither am I. And so the one thing I decided would be of
most value in this introduction would be a summary of how to do
memory access from no less than seven different languages. (Or is it
eight? Well....)
     The title of this section is perhaps a little misleading (on purpose,
of course, as those of you who read my column "Insight: Atari" in
COMPUTE! Magazine can attest). The "common problem" we will
discuss here is not a bug-type problem. Rather, it is a task-type
problem which occurs in many common programs. Or perhaps we
could approach it as a quiz. Why not?

     Quiz: Devise a set of routines which will (1) alter the current
     cursor position (in any standard OS graphics mode) to that
     horizontal and vertical position specified by the variables "H" and
     "V" and (2) retrieve the current cursor position in a like manner.
     To receive full credit for this problem, implement the routine in at
     least seven different computer languages.