APPENDIX TWELVE ___________________________________________________________



The XL/XE Memory Map

Most of the information in the first edition of Mapping the Atari ap-
plies equally well to the XL and XE lines of computers; only those
locations below represent known changes. Atari made several
changes to RAM locations, and the OS was almost entirely rewritten
in the newer models.

The information here pertains to the 600XL, 800XL, 1200XL, 65XE, and
130XE. Except for the 1200XL, the XL and XE models are virtually
identical to each other. There have been changes in the BASIC
ROMs, but I have no official word on any changes in the OS. al-
though I have reason to believe there have been some.

For those owners of XL computers who have difficulty using older 800
software, Atari (and several other companies) makes a Translator
disk which loads an 800 operating system on top of the XL OS, allow-
ing you to run almost all 800 programs. Ask your local Atari dealer
for this disk if you don't already have it. Side A of the Translator disk
permits you to press RESET and usually remain within the older OS;
side B doesn't have this code patch. so it reboots the XL OS when RE-
SET is pressed. A public domain translator called FIXXL is also avail-
able on CompuServe. A hardware solution is available: the XL BOSS
chip from Allen MacroWare.

The DDT subprogram in OSS's MAC/65 assembler is an excellent tool
for examining memory, especially since it gives you the option of
ASCII display and disassembly of visible memory. It allows you to
write directly to memory or jump to any location. I used it constantly
while writing this chapter.

Unless otherwise noted, this material pertains to all XL and XE models
(as does much of the earlier section of the book). RAM locations and
interrupt and OS vectors will remain the same in all systems; how-
ever, the locations and contents of routines they point to may differ
among computers. Not all of the OS ROM locations described here
will be the same in the 1200XL. Some of the changes here are to vec
tors, not to functions. References to function keys (Fl to F4) and LEDs
are for 1200XL users only. My original 1200XL memory map ap-
peared in COMPUTE!'s Third Book of Atari.

Most RAM and hardware locations belonging to the GTIA, ANTIC,
POKEY, and PIA chips (53248-55295; $D000-$D7FF except for PORTB)
have generally not changed. The floating-point package remains at
55296-57343 ($D800-$DFFF), but routines have been altered within it.
The major change in the OS was the shifting of interrupt handlers
from high ROM into the area previously unused between 49152 and
52223 ($C000-$CBFF) and the addition of the international character
set at 52224-53247 ($CC00-$CFFF).