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BASIC OPERATING THEORY
COMMODORE-AMIGA
1000 SYSTEM
SLIDE
2
—
DMA READ
To understand
the
Hardware of the Amiga
1000
System
is
orimarily
a
matte-
of
understanding the
25 DMA,
(Direct
Memory
Access),
Channels
and
their
related
functions.
^<=^ac~
Each
Channel has an
13
Bit Ram Address Pointer which
is
placed
on
the
RAM
Address Bus and
is
used
to
select the location of
the
DMA
Data
Transfer
from
anywhere
in the. 256k, '512K
of RAM.
An 8^Bit Destination Address
is
simultaneously placed on the Register
Address
Bus sending Data
to
one of the
Custom
IC
Addresses.
Almost
all DMA
Channels have
RAM
for
Source
and
Custom
IC
Registers
as
Destination.
SLIDE
4
—
AGNUS BLOCK
<
T?*
!^\^
S
^
the
Address Generator
Chip.
Its
main
function,
in
chip area,
is the
RrtM
Address Generator and Register Address Encoder which provides
all
DMA
Addresses.
nMS
^
836
^
^f
jf
rnade
^P of
approximently 21,000 Transistors
"and
contains
all
DMA Channel Controllers. The Blitter and
the
Copper are also contained
here.
d*
Tl?e
J
e
fi?
ter
Address Encoder
is a
basic PLA type
of
structure that produces
a
Prewired Address on
trie
Register Address,
RGA,
Bus^ whenever
a
DMA
Channel
il
active.
SLIDE
5
—
ADDRESS GENERATOR
The RAM Address
Generator
is
much more complex.
It
contains
an
18
Bit
Pointer
Register,
for
each of
the 25
DMA
Channels,-
Pointer
Restart
Registers
and
Jump
Registers
for
6
of the DMA Channels. The full
18
Bit
Address
carries
out
the
Pointer Increments and adds
for
jumps.
The Priority
Control Logic monitors
the
Pipelined
DMA
Requests
from
each
Controller then stages
the
DMA Cycles based on their Programmed Priority
and
Sync
Counter Time Slot.
It
then tells the 68000 MPU
to
get off the bus using
the
Data
Bus Request, DBR, allowing
AGNUS control.
SLIDE
6
—
COPPER DMA
The Copper uses
1
DMA Channel. The Copper
is
the Co-Processor
that
uses
the
DMA Channels
to
fetch
its
instructions from Memory and write
to
from it's program
in
Memory
to the
Registers
in
itself or
to
the other two Custom
Chips.
The
DMA
Pointer
is the
Instruction Counter
and
must
be
preloaded
with
the
starting
address of
the
Copper's Instructions.
The Copper can also
perform
Move, Wait,
(Halt),
and Ski? Instructions.
MOVi
-
Move Data to a Register
WAIT
-
Wait Until the Electron Beam Passes
a
given position
SKI?
-
Skip Past the next Instruction
if
the Electron 3eam
is
past
a
Given Location
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