Amiga 1000 - Page 29

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