AUTHOR'S PREFACE



Atari memory locations, their labels and their use; a general map
diagram to show how the memory is broken down; an appendix of
utility material with charts and tables, and an index/cross-reference
guide.

There is an awful lot of information contained here; tedious as it might
appear, I suggest that you read this manual through at least once.
Some of the information which is not clear in one area may be
elaborated on and made clearer in another area. Wherever another
location is referred to in one description, you should turn to the
reference and read it after you have read through the first location.
You should also refer to the locations used in any sample program. The
more familiar you are with the memory, the more you will get out of
your Atari. When you read the description in any memory location,
make sure you refer to either the shadow or the hardware register
mentioned for more information.



POWERUP AND RESET
COLD STARTS
On powerup (when you turn on the computer) the Atari OS performs a
number of functions, some of which are noted as defaults in the
memory locations to follow. Among these functions are:

Determine the highest RAM address and clear all RAM to zeroes
(except locations zero to 15; $0 to $F).

Erase and format the device table.

S:, E:, K:, P:, C: handlers, SIO, CIO and interrupt processor are all
initialized.

Set the screen to GRAPHICS mode zero, 24 lines by 40 columns; set
screen margins.

Initialize the cartridge(s) if present; test for the B (right), then for the A
(left) cartridge.

Check the cartridge slots for disk boot instructions and, if they are
present, boot disk.

Transfer control to the cartridge or booted program.

Initialize the RAM interrupt vectors at 512 to 548 ($200 to $224).

Store zero in the following hardware registers: 53248 to 53503, 53760
to 54527 ($D000 - $D0FF, $D200 - $D4FF).

The START key flag is tested and, if set (the START key is held down),
CKEY (74; $4A) requests a cassette boot

HATABS (794; $31A) is initialized to point to the ROM-resident device
handlers.