Amiga 1000 - Page 32

BASIC OPERATING
THEORY
COttlODORZ-AMIGA
1000 SYSTEM
SLIDE
13
—
AUDIO DMA
There
are 4
Audio Controllers.
Each
is independent and
uses 1 DMA
Channel.
(4
Total) Each
Audio Controller fetches its
data curing
a dedicated time
slot
within
Horizontal
Blanking.
Each
Audio Controller can fetch a
Digitized Waveform,
up the 128 K
in
length,
from
anywhere in the
512K
of
memory. Each has a Period,
(Frequency)
, and Volume
Control
Registers.
When eac Audio
Controller is done outputting the
waveform,
it
automatically
restarts itself at the
beginning
and
issues a unique Interrupt.
Each Audio Channel has its
own
on-chip D to
A, (Digital
to Analog)
, Converter
that has 8
Bits
of Data
combined
with 6 Bits
of Volume.
The data
is transferred
under
DMA Control but the Volume
comes from a
Preloaded Register.
Two
of
the Audio Channels
drive
the
Left
Stereo
Output and the other two drive
the
Right Stereo
Output. Channels
can modulate
each
other in both
Frequency
and
Volume which
allows Vibrato
and Whistle effects
to be
created.
DYNAMIC
RAM REFRESH
The Refresh Controller
uses
only 1 DMA Channel
with its own dedicated
time
slots.
Addresses are
placed on the
Memory
Address
Bus during
these slots
in
order
to
Refresh Dynamic RAM.
No Data
Transfer takes place during Refresh
so the
Register Address Bus
is
used
for Chip Synchronizing
Codes
during these time
slots.