APPENDIX TWELVE



Atari promises the XE series will maintain 100 percent compatibility
with the XL series--as long as the software obeys the "rules" and
sticks to official, published vectors and entry points and doesn't try to
take advantage of some ROM routine to save a few bytes (see 62026
and 62128 below). The OS in the XE series is the same as that in the
800XL, at least at the time of this writing. When the ROM routine gets
moved--the software crashes. Don't blame Atari; they've published
this material since day one. If developers don't pay attention, it's not
Atari's fault.

Deleted Registers

The following registers have been completely deleted from the
XL/XE, and other uses have been found for the location (previous
400/800 locations given):

PTEMP (31; $1F)
LINBUF (583-622; $247-$26E)
CSTAT (648; $288)
TMPX1 (668; $29C)
HOLD5 (701; $2BD)
ADDCOR (782; $30E).

00             00             LNFLG
     Used by the Atari in-house debugging programs and OS on
     power-up.

01             01             NGFLAG
     Used during power-up routines for self-testing; checks for bad
     memory bytes; zero means memory failure.

07             07             CMCMD
     Command flag for 835 and 1030 modems set to any nonzero
     number to pass commands to the modem. Used to be TSTDAT.

10,11          A,B            DOSVEC
     Points to 6047 ($179F).

12,13          C,D            DOSINI
     Points to 5440 ($1540).

28-31          1C-1F          ABUFPT
     Intended OS use as buffer pointers; currently unused.

54,55          36,37          LTEMP
     Temporary buffers for the general-purpose peripheral handler
     loader routines. The general-purpose handler routines help the
     OS deal with new handlers and peripherals which load their