Commodore Amiga Quick user guide

Hardware
Reference Manual
Commodore Business Machines, Inc.

Amiga Hardware Reference Manual
Commodore Business Machines, Inc.
Amiga Technical Reference Series
•
••
Addison-Wesley Publishing Company, Inc.
Reading, Massachusetts Menlo Park, California Don Mills, Ontario
Wokingham, England Amsterdam Sydney Singapore Tokyo
Madrid Bogota Santiago San Juan

Library of Congress Cataloging-in-Publication Data
Main entry under title:
Amiga hardware reference manual.
Includes index.
1. Amiga (Computer) I. Commodore Business Machines.
QA76.8.A177A65
1986 004.165 85-26650
ISBN 0-201-1io77-6
BCDEFGHIJ-BA-89876
The text of this manual was written by Robert Peck, Susan Deyl, Jay Miner, and Chris Raymond.
Special
thanks to Bill Kolb, Dave Needle, Lee Ho, and Dale Luck.
COPYRIGHT © 1986 by Commodore-Amiga, Inc.
This manual
is copyrighted and all rights are reserved. This document may not, in whole or in part, be copied, photocopied, repro-
duced, translated or reduced to any electronic medium or machine readable form without prior consent,
in writing, from
Commodore-Amiga, Inc.
DISCLAIMERS
COMMODORE-AMIGA, INC., ("COMMODORE") MAKES NO WARRANTIES, EITHER EXPRESSED OR IMPLIED, WITH
RESPECT
TO THE PROGRAMS DESCRIBED HEREIN, THEIR QUALITY, PERFORMANCE, MERCHANTABILITY, OR FIT-
NESS FOR ANY PARTICULAR PURPOSE. THESE PROGRAMS ARE
SOLD "AS IS." THE ENTIRE RISK AS TO THEIR
QUALITY
AND PERFORMANCE IS WITH THE BUYER. SHOULD THE PROGRAMS PROVE DEFECTIVE FOLLOWING
PURCHASE,
THE BUYER (AND NOT THE CREATOR OF THE PROGRAMS, COMMODORE, THEIR DISTRIBUTORS OR
THEIR RETAILERS) ASSUMES THE ENTIRE COST OF
ALL NECESSARY DAMAGES. IN NO EVENT WILL COMMODORE
BE LIABLE FOR DIRECT, INDIRECT, INCIDENTAL OR CONSEQUENTIAL DAMAGES RESULTING FROM ANY DEFECT
IN THE PROGRAMS EVEN IF
IT HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. SOME LAWS DO NOT
ALLOW THE EXCLUSION OR LIMITATION OF IMPLIED WARRANTIES OR LIABILITIES
FOR INCIDENTAL OR CONSE-
QUENTIAL DAMAGES, SO THE ABOVE LIMITATION OR EXCLUSION
MAY NOT APPLY.
THE AMIGA COMPUTER MEETS TITLE 47 OF THE CODE OF FEDERAL REGULATIONS FOR CLASS B COMPUTING
EQUIPMENT. THE FCC STRICTLY FORBIDS THE USE OF UNSHIELDED CABLE
TO ANY AMIGA CONNECTORS WITH
THE EXCEPTION OF
AC POWER. COMMODORE-AMIGA SHALL NOT BE HELD LIABLE FOR INTERFERENCE GEN-
ERATED BY PERIPHERALS NOT AUTHORIZED IN WRITING BY COMMODORE-AMIGA, INC.
Amiga
is a trademark of Commodore-Amiga, Inc.
CBM Product Number 327272-02
Second Printing, July 1986

PREFACE
This manual provides information about the Amiga[tm] graphics and audio hardware
and about how the Amiga talks
to the outside world through peripheral devices. A por-
tion of this manual
is a tutorial on writing assembly language programs to directly con-
trol the Amiga's graphics and hardware.
This book
is intended for the following audiences:
o Assembly language programmers who need a more direct way of interacting with
the system than the routines described
in the Amiga ROM Kernel Manual. You
can find information here to help you make your programs run faster or do
things
that the ROM kernel routines don't do.
o Anyone who wants
to add new peripherals to the Amiga or just wants to know
how the hardware works.
We suggest
that you use this book according to your level of familiarity with the Amiga
system. Here are some suggestions:
o If this is your initial exposure
to the Amiga, read chapter 1, which gives a sur-
vey of all the hardware features and a brief rundown of graphics and audio
effects created by hardware interaction.
o
If you are already familiar with the system and want to acquaint yourself with
how the various bits in the hardware registers govern the way the system func-
tions, browse through chapters 2 through 8. Examples are included in these
chapters.
o For advanced users, the appendixes give a concise summary of the entire register
set and the uses of the individual bits. Once you are familiar with the effects of
changes in the various bits, you may wish
to refer more often to the appendixes
than to the explanatory chapters.
Here is a brief overview of the contents:
Chapter
1, Introduction. An overview of the hardware and survey of the
Amiga's graphics and audio features.
Chapter
2, Coprocessor Hardware. Using the Copper coprocessor to control the
entire graphics and audio system; directing mid-screen modifications
in graphics
displays and directing register changes during the time between displays.
-v-

Chapter 3, Playfield Hardware. Creating, displaying and scrolling the playfields,
one of the basic display elements of the Amiga; how the Amiga produces multi-
color, multi-graphical bit-mapped displays.
Chapter
4, Sprite Hardware. Using the eight sprite direct-memory access (DMA)
channels to make sprite movable objects; creating their data structures, display-
ing and moving them, reusing the
DMA channels.
Chapter
5, Audz'o Hardware. Overview of sampled sound; how to produce qual-
ity sound, simple and complex sounds, and modulated sounds.
Chapter
6, Blitter Hardware. Using the blitter DMA channel to create anima-
tion effects and draw lines into play
fields.
Chapter 7, System Oontrol Hardware. Using the control registers to define
depth arrangement of graphics objects, detect collisions between graphics
objects, control direct memory access, and control interrupts.
Chapter 8, Interface Hardware.
How the Amiga talks to the outside world
through controller ports, keyboard, audio jacks and video connectors, serial and
parallel interfaces; information about the disk controller and RAM expansion
slot.
Appendixes. Alphabetical and address-order listings of all the graphics and
audio system registers and the functions of their bits, system memory map,
descriptions of internal and external connectors, specifications for the peripheral
interface ports, and specifications for the keyboard.
Glossary. After the appendixes, there is a glossary of important terms.
You may wish to look
at the following books and manuals for further information about
the Amiga:
o The Amiga
ROM Kernel Manual contains information about the Exec multitask-
ing routines and is the source for all the C language primitives for Amiga graph-
ics, animation, and audio.
o The following manuals contain information about the AmigaDOS operating sys-
tem:
o AmigaDOS User's Manual
-vi-

o AmigaDOSDeveloper's Manual
o AmigaDOS Technical Reference Manual
It is our policy to make certain that the information contained here is accurate, con-
sistent, and up
to date. If you should find any material confusing, inaccurate, or incom-
plete, please feel free to contact Amiga with your questions or comments.
-vii-

Table of Contents
Chapter 1 INTRODUCTION ............................................................................................ 1
Components of the Amiga ........................................................................................... 1
THE MO 68000 AND THE AMIGA SPEOIAL-PURPOSE
lIARDW
ARE ..................................................................................................................... 2
VOR AND DIREOT OAMERA INTERFAOE
..................................................... 5
PRIMARY AND SEOONDARY MEMORY
......................................................... 5
PERIPHERALS
................................................................................................................ 5
System Expandability and Adaptability .......................................................... 6
Chapter 2 COPROCESSOR HARDWARE .......................................................... 7
Introduction ............................................................................................................................. 7
ABOUT THIS OHAPTER ............................................................................................ 8
What is a Copper Instruction? ................................................................................. 8
The MOVE Instruction
.................................................................................................. 9
The WAIT Instruction .................................................................................................... 11
HORIZONTAL BEAM POSITION .......................................................................... 12
VERTIOAL BEAM POSITION ................................................................................. 12
THE OOMPARISON ENABLE BITS ..................................................................... 13
Using the Copper Registers ......................................................................................... 13
LOOATION REGISTERS ............................................................................................ 13
JUMP STROBE ADDRESS
......................................................................................... 14
OONTROL REGISTER ................................................................................................ 14
Putting Together a Copper Instruction List ................................................. 15
OOMPLETE SAMPLE OOPPER LIST ................................................................. 17
LOOPS AND BRANOHES .......................................................................................... 19
Starting and Stopping the Copper ........................................................................ 19
STARTING
THE OOPPER AFTER RESET ...................................................... 19
STOPPING THE OOPPER ........................................................................................ 19
Advanced Topics ................................................................................................................. 20
THE SI(IP INSTRUOTION ........................................................................................ 20
OOPPER LOOPS AND BRANOHES AND OOMPARISON
ENABLE
.............................................................................................................................. 21
USING
THE COPPER IN INTERLACED MODE ........................................... 22
USING
THE OOPPER WITH THE BLITTER .................................................. 23
THE COPPER AND THE 68000 .............................................................................. 24
Summary of Copper Instructions ........................................................................... 24
-ix-

Chapter 3 PLAYFIELD HARDWARE ..................................................................... 27
Introduction .......................................................................................................... ,.................. 27
ABOUT THIS CIIAPTER
............................................................................................ 28
PLAYFIELD FEATURES
............................................................................................ 28
Forming a Basic Playfield ............................................................................................ 33
HEIGHT AND WIDTH
OF THE PLAYFIELD .................................................. 34
BIT-PLANES AND COLOR ....................................................................................... 34
SELECTING RESOLUTION
...................................................................................... 38
ALLOCATING MEMORY
FOR BIT-PLANES .................................................. 41
CODING
THE BIT-PLANES FOR CORRECT COLORING ...................... 44
DEFINING
THE SIZE OF THE DISPLAY WINDOW................................... 46
TELLING
THE SYSTEM HOW TO FETCH AND DISPLAY
DATA
................................................................................................................................... 49
DISPLAYING AND REDISPLAYING THE PLAYFIELD ............................. 52
ENABLING THE COLOR DISPLAY
..................................................................... 52
SUMMARY
......................................................................................................................... 53
EXAMPLES
OF FORMING BASIC PLAYFIELDS .......................................... 55
Forming a Dual-playfield Display .......................................................................... 58
Bit-Plane Assignment in Dual-playfield Mode ............................................. 60
COLOR REGISTERS IN DUAL-PLAYFIELD MODE .................................... 62
DUAL-PLAYFIELD PRIORITY AND CONTROL
........................................... 64
ACTIVATING DUAL-PLAYFIELD MODE
......................................................... 64
SUMMARY
......................................................................................................................... 65
Bit-planes and Display Windows of All Sizes ............................................... 65
WHEN THE BIG PICTURE IS LARGER THAN
THE DISPLAY
WINDOW
........................................................................................................................... 65
MAXIMUM DISPLAY WINDOW SIZE
................................................................. 72
Moving (Scrolling) Playfields ..................................................................................... 73
VERTICAL SCROLLING ............................................................................................ 73
HORIZONTAL SCROLLING
..................................................................................... 74
SUMMARY ......................................................................................................................... 78
Advanced Topics ................................................................................................................. 79
INTERACTIONS- PLAYFIELDS AND OTHER OBJECTS .................... 79
HOLD-AND-MODIFY MODE
.................................................................................... 79
FORMING A DISPLAY WITH SEVERAL DIFFERENT
PLA YFIELDS .................................................................................................................... 82
USING AN EXTERNAL VIDEO SOURCE
......................................................... 82
SUMMARY
OF PLAYFIELD REGISTERS ......................................................... 83
Summary of Color Selection ....................................................................................... 86
COLOR REGISTER CONTENTS ........................................................................... 86
SOME SAMPLE COLOR REGISTER CONTENTS ........................................ 86
COLOR SELEOTION IN LOW-RESOLUTION MODE ................................ 87
COLOR SELEOTION IN HOLD-AND-MODIFY MODE
............................... 89
COLOR SELEOTION IN HIGH-RESOLUTION MODE
................................ 89
-x-

Chapter 4 SPRITE HARDWARE ................................................................................. 91
Introduction ............................................................................................................................. 91
ABOUT THIS ClIAPTER ............................................................................................ 92
Forming a Sprite ................................................................................................................. 92
SCREEN POSITION ...................................................................................................... 92
SIZE OF SPRITES .......................................................................................................... 95
SlIAPE
OF SPRITES ..................................................................................................... 95
SPRITE COLOR
.............................................................................................................. 96
DESIGNING A SPRITE
............................................................................................... 98
BUILDING THE DATA STRUCTURE .................................................................. 99
Displaying a Sprite ............................................................................................................ 104
SELECTING A DMA CHANNEL AND SETTING THE
POINTERS
......................................................................................................................... 105
RESETTING THE ADDRESS POINTERS .......................................................... 106
SPRITE DISPLAY EXAMPLE .................................................................................. 106
Moving a Sprite .................................................................................................................... 108
Creating Additional Sprites ........................................................................................ 110
Reusing Sprite DMA Channels ................................................................................. 111
Overlapped Sprites ............................................................................................................ 114
Attached Sprites ...................................................................................................... ;........... 116
Manual Mode ......................................................................................................................... 119
Sprite Hardware Details ................................................................................................. 120
.Summary of Sprite Registers ..................................................................................... 124
POINTERS ......................................................................................................................... 124
CONTROL REGISTERS ............................................................................................. 125
DATA REGISTERS ........................................................................................................ 126
Summary of Sprite Color Registers ...................................................................... 127
Chapter 5 AUDIO HARDWARE ................................................................................... 131
Introduction ............................................................................................................................. 131
INTRODUCING SOUND GENERATION ........................................................... 132
THE AMIGA SOUND HARDWARE ....................................................................... 135
Forming and Playing a Sound .................................................................................. 136
DECIDING WHICH CHANNEL TO USE ............................................................ 136
CREATING THE WAVEFORM DATA ................................................................ 137
TELLING THE SYSTEM ABOUT THE DATA ................................................ 138
SELECTING THE VOLUME ..................................................................................... 139
SELECTING THE DATA OUTPUT RATE ........................................................ 140
PLAYING THE WAVEFORM ................................................................................... 143
STOPPING THE AUDIO DMA ................................................................................ 144
SUMMARY .... ,.................................................................................................................... 145
EXAMPLE .......................................................................................................................... 145
Producing Complex Sounds ........................................................................................ 147
JOINING TONES ........................................................................................................... 147
-xi-

PLAYING MULTIPLE TONES AT THE SAME TIME ................................. 149
MODULATING SOUND
.............................................................................................. 149
Producing High-quality Sound ............................................................................ :.... 152
MAKING WAVEFORM TRANSITIONS
.............................................................. 152
SAMPLING RATE
.......................................................................................................... 152
EFFICIENCY
.................................................................................................................... 153
NOISE REDUCTION
..................................................................................................... 154
ALIASING DISTORTION
........................................................................................... 154
LOW-PASS FIL
TER ................................................................ ,...................................... 156
Using Direct (Non-DMA) Audio Output .......................................................... 157
The Equal-tempered Musical Scale ....................................................................... 158
Decibel Values for Volume Ranges ....................................................................... 160
The Audio State Machine ............................................................................................ 161
Chapter 6 BLITTER HARDWARE ............................................................................ 165
Introduction ............................................................................................................................. 165
Data Copying ......................................................................................................................... 167
Pointers and Modulos ...................................................................................................... 168
Ascending and Descending Addressing .............................................................. 170
Rectangular or Linear Address Scanning ......................................................... 171
Blitter Logic Operations ................................................................................................ 171
DESIGNING THE LF CONTROL BYTE WITH LOGIC
EQUATIONS
................................................... ................................................................. 172
DESIGNING THE LF CONTROL BYTE WITH VENN
DIAGRAMS
........................................................................................................................ 175
Shifting ........................................................................................................................................ 177
Masking ...................................................................................................................................... 178
Zero Detection ....................................................................................................................... 179
Area Filling .............................................................................................................................. 180
INCLUSIVE (NORMAL) AREA FILLING
........................................................... 180
EXCLUSIVE AREA FILLING
.................................................................................... 182
Line Drawing .......................................................................................................................... 1$3
OCTANTS IN LINE DRAWING
.............................................................................. 184
Blitter Operations and System DMA .................................................................. 186
BLITTER DMA PRIORITY
........................................................................................ 186
DMA TIME SLOT ALLOCATION
.......................................................................... 186
BIT-PLANE/PROCESSOR BUS SHARING
........................................................ 189
EFFECTS
OF DIFFERENT DISPLAY SIZES ................................................... 191
EFFECTS OF BLITTER OPERATION
................................................................ 191
Complete Blitter Example ........................................................................................... 193
Blitter Block Diagram ..................................................................................................... 195
-xii-

Chapter 7 SYSTEM CONTROL HARDWARE ............................................... 197
Introduction ............................................................................................................................. 197
Video Priorities ..................................................................................................................... 198
FIXED SPRITE PRIORITIES
.................................................................................... 198
HOW SPRITES ARE GROUPED
............................................................................ 199
UNDERSTANDING VIDEO PRIORITIES
.......................................................... , 199
SETTING THE PRIORITY CONTROL REGISTER
...................................... 200
Collision Detection ............................................................................................................. 202
HOW COLLISIONS ARE DETERMINED
........................................................... 202
HOW TO INTERPRET THE COLLISION DATA
........................................... 202
HOW COLLISION DETECTION
IS CONTROLLED ..................................... 203
Beam Position Detection ............................................................................................... 205
USING THE BEAM POSITION COUNTER
...................................................... 205
Interrupts .................................................................................................................................. 207
NONMASI<ABLE INTERRUPT
............................................................................... 207
MASKABLE INTERRUPTS
....................................................................................... 207
USER INTERFACE TO THE INTERRUPT SYSTEM
.................................. 207
INTERRUPT CONTROL REGISTERS
................................................................ 208
SETTING AND CLEARING BITS
.......................................................................... 208
DMA Control ......................................................................................................................... 212
Chapter 8 INTERFACE HARDWARE .................................................................... 215
Introduction ............................................................................................................................. 215
Controller Port Interface .............................................................................................. 216
READING THE CONTROLLER
PORT ............................................................... 217
Disk Controller ..................................................................................................................... 227
DISK SELECTION, CONTROL, AND SENSING
............................................ 228
OTHER REGISTERS IN DISK OPERATIONS
............................... :................. 232
DISI( INTERRUPTS
...................................................................................................... 235
The I(eyboard ........................................................................................................................ 236
HOW THE KEYBOARD DATA
IS RECEIVED ................................................ 236
TYPE OF DATA RECEIVED .................................................................................... 236
LIMITATIONS
OF THE KEYBOARD .................................................................. 239
Parallel Input/Output Interface ............................................................................. 240
Serial Interface ...................................................................................................................... 240
INTRODUCTION
TO SERIAL CIRCUITRy..................................................... 240
SETTING THE
BAUD RATE .................................................................................... 240
SETTING THE RECEIVE MODE
........................................................................... 241
CONTENTS
OF THE RECEIVE DATA REGISTER ..................................... 241
HOW OUTPUT DATA
IS TRANSMITTED ....................................................... 243
SPECIFYING THE REGISTER CONTENTS
.................................................... 244
Audio Output Connections ......................................................................................... 245
Display Output Connections ...................................................................................... 245
-xiii-

Appendix A Register Summary-Alphabetical Order ...................................... A-I
Appendix B Register Summary-Address Order .................................................. B,..1
Appendix C Custom Chip Pin Allocation List ....................................................... C-l
Appendix D System Memory Map .............................................................................. ~... D-l
Appendix E Interfaces ................................................................................................................ B-1
Appendix F Peripheral Interface Adapters ................................................................ F-I
Appendix G Amiga Auto-configuration Architecture
....................................... G-l
Appendix H I<eyboard ............................................................................................................... H-l
Glossary ................................................................................................................................ Glossary-l
Index ......................................................................................................................................... Index-l
-XIV-

Figures
Figure 2-1 Interlaced Bit-Plane in RAM -400 Lines Long ................................................................. 23
Figure 3-1 How the Video Display Picture Is Produced ...................................................................... 29
Figure,3-2 What Is a Pixel? ................................................................................................................................... 30
Figure 3-3 How Bit-planes Select a Color ..................................................................................................... 32
, Figure 3-4 Significance of Bit-Plane Data in Selecting Colors ......................................................... 33
Figure 3-5 Interlacing ................................................................................................................................................ 39
Figure 3-6 Effect of Interlaced Mode on Edges of Objects ................................................................. 40
Figure 3-7 Memory Organization for a Basic Bit-Plane ....................................................................... 43
Figure 3-8 Combining Bit-planes ....................................................................................................................... 45
Figure 3-9 Positioning the On-screen Display .............................................. __ ........................................... 47
Figure 3-10 Data Fetched for the First Line When Modulo = 0 ......................................... .-...... 50
Figure 3-11 Data Fetched for the Second Line When Modulo = 0 ............................................. 51
Figure 3-12 A Dual-playfield Display .............................................................................................................. 59
Figure 3-13 How Bit-Planes Are Assigned to Dual Playfields .......................................................... 61
Figure 3-14 Memory Picture Larger than the Display .......................................................................... 66
Figure 3-15 Data Fetch for the First Line When Modulo = 40..................................................... 67
Figure 3-16 Data Fetch for the Second Line When Modulo = 40 ................................................ 67
Figure 3-17 Data Layout for First Line-Right Half of Big Picture ............................................ 68
Figure 3-18 Data Layout for Second Line-Right Half of Big Picture ....................................... 68
Figure 3-19 Display Window Horizontal Starting Position ................................................................ 70
Figure 3-20 Display Window Vertical Starting Position ..................................................................... 70
Figure 3-21 Display Window Horizontal Stopping Position .............................................................. 71
Figure 3-22 Display Window Vertical Stopping Position .................................................................... 72
Figure 3-23 Vertical Scrolling .............................................................................................................................. 74
Figure 3-24 Horizontal Scrolling ......................................................................................................................... 75
Figure 3-25 Memory Picture Larger Than the Display Window.................................................... 77
Figure 3-26 Data for Line 1 - Horizontal Scrolling ................................................................................. 77
Figure 3-27 Data for Line 2 - Horizontal Scrolling ................................................................................. 77
Figure 4-1 Defining Sprite On-screen Position .......................................................................................... 93
Figure 4-2 Position of Sprites .............................................................................................................................. 94
Figure 4-3 Shape of Spaceship ............................................................................................................................. 96
Figure 4-4 Sprite with Spaceship Shape Defined ..................................................................................... 96
Figure 4-5 Sprite Color Definition ..................................................................................................................... 97
Figure 4-6 Color Register Assignments .......................................................................................................... 98
Figure 4-7 Data Structure Layout .................................................................................................................... 101
-xv-

Figure 4-8 Sprite Priority ....................................................................................................................................... 111
Figure 4-9 Typical Example of Sprite Reuse .............................................................................................. 112
Figure 4-10 Typical Data Structure for Sprite Re-use ......................................................................... 113
Figure 4-11 Overlapping Sprites (Not Attached) ..................................................................................... 115
Figure 4-12 Placing Sprites Next to Each Other ..................................................................................... 116
Figure 4-13 Sprite Control Circuitry ............................................................................................................... 122
Figure 5-1 Sine Waveform ..................................................................................................................................... 133
Figure 5-2 Digitized Amplitude Values .......................................................................................................... 135
Figure 5-3 Example Sine Wave ........................................................................................................................... 142
Figure 5-4 Waveform with Multiple Cycles ................................................................................................ 153
Figure 5-5 Frequency Domain Plot of Low-Pass Filter ........................................................................ 155
Figure 5-6 Noise-free Output (No Aliasing Distortion) ........................................................................ 155
Figure 5-7 Some Aliasing Distortion ................................................................................................................ 156
Figure 5-8 Audio State Diagram ........................................................................................................................ 164
Figure 6-1 How Images are Stored in Memory .......................................................................................... 168
Figure 6-2 Bit-plane Image Larger than the Blitter Source Window........................................... 169
Figure 6-3 Blitter Minterm Venn Diagram .................................................................................................. 176
Figure 6-4 A Packed Font ..................................................................................................................................... 178
Figure 6-5 Blitter Masking Example ................................................................................................................ 179
Figure 6-6 Area-fill Example -Bar Chart ................................................................................................. 180
Figure 6-7 Use of the FCI Bit -Bit Is a 0 .................................................................................................... 181
Figure 6-8 Use of the FCI Bit -Bit Is a 1 .................................................................................................... 182
Figure 6-9 Single-Point Vertex Example ....................................................................................................... 183
Figure 6-10 Octants for Line Drawing ............................................................................................................ 185
Figure 6-11 DMA Time Slot Allocation ......................................................................................................... 188
Figure 6-12 Normal 68000 Cycle ........................................................................................................................ 189
Figure 6-13 Time Slots Used by a Six-bit-plane Display..................................................................... 190
Figure 6-14 Time Slots Used by a High-resolution Display............................................................... 190
Figure 7-1 Inter-Sprite Fixed Priorities .......................................................................................................... 198
Figure 7-2 Analogy for Video Priority ............................................................................................................ 199
Figure 1-1 Controller Plug and Computer Connector .......................................................................... 216
Figure 1-2 Typical Paddle Controller Connection .................................................................................. 221
Figure 1-3 The Amiga Keyboard, Showing Keycodes in Hexadecimal....................................... 239
Figure 1-4 Starting Appearance ofSERDAT and Shift Register ................................................... 244
Figure 1-5 Ending Appearance of Shift Register ...................................................................................... 244
-xvi-

Chapter 1
INTRODUCTION
The Amiga is a low-cost, high-performance computer with advanced graphics and sound
features. This chapter describes the Amiga's hardware components and gives a brief
overview of its graphics and sound features.
Components of the Amiga
These are the hardware components of the Amiga:
Introduction 1

o Motorola Me 68000 16/32-bit main processor.
o 256K bytes of internal RAM, expandable to 512K.
o 256K bytes of ROM containing a real-time, multi-tasking operating system with
sound, graphics, and animation
support routines.
o Built-in 3 1/2-inch double-sided disk drive.
o Expansion disk
port for connecting up to three additional disk drives, which may be
either 3-1/2 inch or 5-1/4 inch, double-sided.
o Fully programmable serial port.
o Fully programmable parallel port.
o Two-button opto-mechanical mouse.
o
Two reconfigurable controller ports (for mice, joysticks, paddles, or custom
controllers).
o
Detach~d 89-key keyboard with calculator pad, function keys, and cursor keys.
o
Ports for simultaneous composite video and analog or digital RGB output.
o Ports for audio output to left and right stereo channels from four special-purpose
audio channels.
o Expansion connector
that allows you to add RAM, additional disk drives (floppy or
hard), peripherals, or coprocessors.
THE MC 68000 AND THE AMIGA SPECIAL-PURPOSE HARDWARE
The Motorola 68000 is a 16/32-bit microprocessor operating at 7.16 megahertz. In the
Amiga, the 68000 can address over 8 megabytes of contiguous random access memory
(RAM).
The performance of the 68000 is enhanced by a system design that gives it every alter-
nate bus cycle, allowing it to run at full rated speed most of the time. As described in
the section below, the special-purpose hardware can steal time from the 68000 for jobs it
can do more efficiently
than the 68000. Even then, such cycle stealing only blocks the
68000's access
to the shared memory. When using ROM or external memory, the 68000
always runs
at full speed.
2 Introduction

Among other functions, the special-purpose hardware provides the following:
o Bit-plane-generated high-resolution graphics typically producing 320 by 200 non-
interlaced displays and 320 by 400 interlaced displays
in 32 colors, and 640 by 200
non-interlaced or
640 by 400 interlaced displays in 16 colors. There is also a special
mode
that allows you to have up to 4,096 colors on-screen simultaneously.
o A custom display coprocessor
that allows changes to most of the special-purpose
registers
in synchronization with the position of the video beam. This allows such
special effects as mid-screen changes to the color palette, splitting the screen into
multiple horizontal slices, each having different video resolutions and color depths,
beam-synchronized interrupt generation for the 68000, and more.
The coprocessor
can trigger many times per screen.
It can trigger in the middle of lines, as well as at
the beginning or during the blanking interval. The coprocessor itself can directly
affect most of the registers of the special-purpose hardware, freeing the 68000 for
general-purpose computing tasks.
o 32 system color registers, each of which contains a twelve-bit number as four bits of
RED, four bits of GREEN, and four bits of BLUE intensity information. This
allows a system color palette of 4,096 different choices of color for each register.
Although an RGB monitor provides the best available
output for the system graph-
ics, text, and color, the composite video signal has been carefully designed
to provide
maximum NTSC compatibility. This signal may be video-taped or fed
to a standard
composite video monitor.
o Eight reusable 16-bit-wide sprites with up
to 15 color choices per sprite pixel (when
sprites are paired). A sprite is an easily movable graphics object whose display
is
entirely independent of the background {called a playfield)j sprites can be displayed
"over" or "under" this background. A sprite
is 16 low-resolution pixels wide and an
arbitrary number of lines tall. After producing the last line of a sprite on the screen,
a sprite DMA (direct memory access) channel may be used
to produce yet another
sprite image elsewhere on-screen (with
at least one horizontal line between each
reuse of a sprite processor). Thus, you can produce many small sprites by simply
reusing the sprite processors appropriately.
o Dynamically-controllable inter-object priority, with collision detection. This means
that the system can dynamically control the video priority between the sprite
objects and the bit-plane backgrounds (playfields). You can control which object or
objects appear "on top"
at any time.
Additionally, you can use system hardware to detect collisions between objects and
have your program react to such collisions.
Introduction 3

o Custom bit-blitter used for high speed data movement, adaptable to bit-plane ani-
mation.
The blitter has been designed to efficiently retrieve data from up to three
sources, combine the
data in one of 256 different possible ways, and optionally store
the combined
data in a destination area. This is one of the situations where the
68000 gives up memory cycles
to a DMA channel that can do the job more
efficiently.
The bit-blitter, in a special mode, draws patterned lines into rectangu-
larly organized memory regions
at a speed of about 1 million dots per second; and it
can efficiently handle area fill.
o Audio consisting of four low-noise digital channels with independently programmable
volume and sampling rate.
The audio channels retrieve their control and data via
direct memory access. Once started, each channel can automatically
playa specified
waveform without further processor interaction. Two channels are directed into
each of the two stereo audio outputs.
The audio channels may be linked together if
desired
to provide amplitude or frequency modulation or both forms of modulation
simultaneously.
o DMA-controlled floppy disk read and write on a full-track basis. This means
that
the built-in disk can read something over 5.6K bytes of data in a single disk revolu-
tion
(11 sectors of 512 bytes each).
All of the special functions described above are produced by three custom-designed VLSI
circuits, which work in concert with the 68000. These circuits and the 68000 use the
shared memory on a fully interleaved basis. Since the 68000 only needs
to access the
memory bus during each alternate clock cycle in order
to run full-speed, the rest of the
time the memory bus is free for other activities.
The special-purpose hardware uses the memory bus during these free cycles, effectively
allowing the 68000
to run at full rated speed most of the time. We say "most of the
time" because there are some occasions when the special-purpose hardware steals
memory cycles from the 68000,
but with good reason. Specifically, the coprocessor and
the data-moving DMA channel called the blitter can each steal time from the 68000 for
jobs they can do better than the 68000. Thus, the system DMA channels are designed
with maximum performance
in mind; the job to be done is performed by the most
efficient hardware element available. In addition, sprites, audio, and disk
DMA also
steal cycles when
in operation.
Another primary feature of the Amiga hardware is the ability
to dynamically control
which
part of memory is used for the background display, audio, and sprites. The
Amiga is not limited to a small, specific area of RAM for a frame buffer. Instead, the
system allows display bit-planes, sprite-processor control lists, coprocessor instruction
lists, or audio channel control lists to be located anywhere within the lowest 512K of the
memory map.
4 Introduction

This same region of memory can be accessed by the bit-blitter. This means, for exam-
ple,
that the user can store partial images at scattered areas of memory and use these
images for animation effects by rapidly replacing on-screen material while saving and res-
toring background images.
In fact, the Amiga includes firmware support for display
definition and control as well as support for animated objects embedded within
playfields.
VCR AND DffiECT CAMERA INTERFACE
In addition to the connections for NTSC composite Amiga video and both digital and
analog RGB monitors, the system can be expanded to include a VCR or camera inter-
face. This system is capable of synchronizing with an external video source and replac-
ing the system background color with the external image. This allows for the develop-
ment of fully integrated video images with computer-generated graphics. Laser disk
input is accepted in the same manner.
PRIMARY AND SECONDARY MEMORY
Primary memory in the Amiga consists of 256K bytes of ROM and 256K bytes of RAM.
A RAM expansion cartridge is available as an option. Secondary memory is provided by
a built-in 3 1/2-inch floppy disk drive. Disks are SO-track, double-sided, and formatted
as
11 sectors per track, 512 bytes per sector (over 900,000 bytes per disk). A special util-
ity can read and write disk files compatible with the Apple II[tm]. In addition, the disk
controller can read and write 320/360K
IBM PC[tm] formatted disks. External 3 1/2-
inch
or 5 1/4-inch disk drives can be added to the system through the expansion
connector.
PERIPHERALS
Circuitry for some of the peripherals resides on one of the custom chips; other chips han-
dle various signals not specifically assigned to any of the custom chips, including modem
controls, disk status sensing, disk motor and stepping controls, ROM enable, parallel
input/output interface, and keyboard interface.
The Amiga includes a standard RS-232-C serial port for external serial input/output
devices.
A detached, professional-quality keyboard
is included in the base system. You can store
the keyboard beneath the system cabinet. For maximum flexibility, both key-down and
key-up signals are sent.
Introduction 5

For those who prefer incremental cursor control, there are cursor keys on the keyboard.
You can attach many other types of controllers through the two controller ports on the
side of
the base unit. You can use a mouse, joystick, keypad, trackball, or steering
wheel controller in either of the controller ports. (A light pen can be attached
to port 0.)
...,
I
System Expandability and Adaptability
You can add peripheral devices to the Amiga's expansion connector, add additional
external RAM on the same expansion connector,
or upgrade internal RAM to 512K.
Additional disk units may be daisy-chained from a connector
at the rear of the unit for a
total of three extra drives.
The system software is highly adaptable to other host operating systems. The Amiga's
graphics support routines are designed to make the user interface as friendly as possible.
New peripheral devices are recognized and used by system software through a well-
defined, well-documented linking procedure.
6 Introduction