Atari 400 Technical Reference Manual page 155

11 ADVANCED TECHNIQUES AND APPLICATION NOTES
This section presents information to use the capabilities of the OS
and some of the hardware capabilites that aren't directly available
through the OS ,and in fact, can be in direct conflict with parts of
the OS.
SOUND GENERATION
The OS uses the POKEY sound generation capabilities only in the I/O
SUbsystem, for cassette FSK tone generation, and for the "nois~
bus" option in SIO.
Capabilities
The hardware provides four
independentl~
programmable audio
channels that are mixed and sent to the television set as part of
the composite video signal. The POKEY registers shown below are all
concerned with sound control (as described in the ATARI Home
Computer Hardware Manual>.
AUDCTL
AUDC1
AUDC2
AUDC3
AUDC4
[D208J
[D201J and AUOF1 [D200J
[D203J and AUOF2 [D202J
[D205] and AUOF3 [0204]
[D207] and AUOF4 [0206]
Audio control.
Channel 1 control.
Channel 2 control.
Channel 3 control.
Channel 4 control.
Conflicts With OS
There are two potential conflicts with the
as
involving sound
generation:
o The OS can generate its own sounds and then turn off all sounds
as part of 1/0 operations to the cassette and the serial bus
peripherals.
o The OS does not turn off sounds when you press [SYSTEM.RESETJ or
[BREAK]. If the sounds are to be turned off under those
conditions, the controlling program must provide that capability.
OPERATING SYSTEM C016555 -- Section 11
170