AUTHOR'S PREFACE



(D:) Disk Drive
(F:) Screen Editor
(S:) Display
(K:) Keyboard
(P:) Printer
(C:) Cassette
(R:) RS-232 interface. (Don't confuse this with (R) for Read.) The
     context should be obvious.

(number) e.g. (708) Shadow Register. This is a RAM register which
corresponds to a ROM register in one of the special Atari chips such as
GTIA or POKEY. The shadow location is the address you use to PEEK
and POKE values. These shadow locations are polled by the hardware
addresses 30 times a second at every stage two VBLANK interval, and
the values used are transferred to the hardware locations for use. In
order to effect any "permanent" change to the hardware location, you
have to use the shadow register in BASIC (of course, every change is
negated when you turn the machine off!). Only machine language is
fast enough to use the hardware addresses directly.

For example, location 54273 is for character control. It polls location
755 to see if the screen characters are to be normal, inverse, or upside-
down. To change the characters, you POKE location 755--the shadow
--not 54273. If you POKE 54273, you will get the desired effect--for
1/60 of a second! As mentioned above, you can use the hardware
addresses directly in machine language, but not in BASIC. It's just too
slow.
Sometimes, where most appropriate, a hexadecimal number will be
displayed and the decimal number put in parentheses. The context
should be obvious concerning which is a shadow or a decimal number.

(* letter) refers to a source in the case of a conflicting location
     or explanation. See the source below.

($number) refers to a hexadecimal (also called hex) number
     (i.e.: $D40E). I also refer to "pages" in memory. Pages are
     sections of 256 bytes ($100) of memory which end with 00 (i.e.:
     $E200, $C000, $600). Four pages ($400) equals 1024 bytes or 1K
     (kilobyte) of memory.

GLOSSARY
ANTIC, CTIA AND GTIA, PIA, POKEY: Special Atari
     chips controlling the 400/800's graphics, color and screen
     resolution, controller jacks and sound, respectively. Located in
     ROM, locations 53248 to 54783. ANTIC also processes the Non-
     Maskable Interrupts and POKEY processes the Interrupt Requests.
     These chips, along with the 6502 microprocessor which runs the
     rest of the Atari, are housed inside your computer, protected by