Commodore Amiga A1000, Hardware Reference Manual

Page: 12 / 380

In addition to the 68000, the Amiga contains special purpose hardware known as the
"custom chips" that greatly enhance system performance. The term "custom chips" refers
to the 3 integrated circuits which were designed specifically for the Amiga computer.
These three custom chips (called Agnus, Paula, and Denise) each contain the logic to
handle a specific set of tasks, such as video, sound, direct memory access (DMA),
or graphics.
Among other functions, the custom chips provide the following:
 Bitplane generated, high resolution graphics capable of supporting both PAL and
NTSC video standards.
o
On NTSC systems the Amiga typically produces a 320 by 200 non-interlaced
or 320 by 400 interlaced display in 32 colors and a 640 by 200 non-
interlaced or 640 by 400 interlaced display in 16 colors.
o
On PAL systems, the Amiga typically produces a 320 by 256 non-interlaced
or 320 by 512 interlaced display in 32 colors, and a 640 by 256 non-
interlaced or 640 by 512 interlaced display in 16 colors.
Additional video modes allow for the display of up to 4,096 colors on screen
simultaneously (hold-and-modify) or provide for larger, higher resolution displays
(overscan).
 A custom display co-processor 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 co-processor
can trigger many times per screen, in the middle of lines, and at the beginning or
during the blanking interval. The co-processor itself can directly affect most of the
registers in the other custom chips, freeing the 68000 for general computing tasks.
 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.
 Eight reusable 16 bit wide sprites with up to 15 color choices per sprite pixel (when
sprites arc paired). A sprite is an easily movable graphics object whose display is
entirely independent of the background (called a playfield); 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 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, many small sprites can be produced by simply reusing the
sprite processors appropriately.
 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 bitplane backgrounds (playfields). You can control which object or
objects appear over or under the background at any time.