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
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