Atari 400 Technical Reference Manual page 142

10 PROGRAM ENVIRONMENT AND INITIALIZATION
This section discusses possible alternative software environments
using OS Configurations. Environments other than those discussed
here are also possible. A thorough understanding of the power-up
and system reset processes (see Section 7) will be necessary to
evaluate all alternative environments.
CARTRIDGE
Most games (and some language processors) are supported via the
cartridge environment. The cartridge resident software is in
control of the system, sometimes using the
as
and sometimes not.
A cartridge can specify whether the diskette is to be booted at
power-up time, whether the cartridge is to provide the
controlling software, or whether the cartridge is a special
diagnostic cartridge. These options are specified by bits in the
cartridge header, as shown below:
+----------------+
cartridge
BFFA (9FFA for cartridge B)
+- -+
: start address
+----------------+
00
+----------------+
option byte
+----------------+
cartridge
+- -+
init address BFFF (9FFF for cartridge B)
+----------------+
Figure
10-1
Cartridge Header Format
The byte of
"00"
is used to allow the OS to determine when a
cartridge is inserted; locations BFFC and 9FFC will not read zero
when there is neither RAM at those locations nor a cartridge
inserted. RAM is differentiated from a cartridge by its ability
to be altered.
OPERATING SYSTEM C016555 -- Section
10
157