The color table contains 32 registers, and you may load a different color
into each of the registers. Here is a condensed view of the contents of
the color table:
Register Name Contents Meaning
------------- -------- -------
COLOR00 12 bits User-defined color for the
background area and borders.
COLOR01 12 bits User-defined color number 1
(For example, the alternate color
selection for a two-color playfield).
COLOR02 12 bits User-defined color number 2.
. .
. .
. .
COLOR31 12 bits User-defined color number 31.
Table 3-2: Portion of the Color Table
COLOR00 is always reserved for the background color. The background color
shows in any area on the display where there is no other object present
and is also displayed outside the defined display window, in the border
area.
Genlocks and the background color.
---------------------------------
If you are using the optional genlock board for video input from a
camera, VCR, or laser disk, the background color will be replaced by
the incoming video display.
Twelve bits of color selection allow you to define, for each of the 32
registers, one of 4,096 possible colors, as shown in Table 3-3.
Bits Color
---- -----
Bits 15 - 12 Unused
Bits 11 - 8 Red
Bits 7 - 4 Green
Bits 3 - 0 Blue
Table 3-3: Contents of the Color Registers
Table 3-4 shows some sample color register bit assignments and the
resulting colors. At the end of the chapter is a more extensive
Color Register list .
Contents of the Resulting
Color Register Color
--------------- ---------
$FFF White
$6FE Sky blue
$DB9 Tan
$000 Black
Table 3-4: Sample Color Register Contents
Some sample instructions for loading the color registers are shown below:
LEA CUSTOM,a0 ; Get base address of custom hardware...
MOVE.W #$FFF,COLOR00(a0) ; Load white into color register 0
MOVE.W #$6FE,COLOR01(a0) ; Load sky blue into color register 1
The color registers are write-only.
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Only by looking at the screen can you find out the contents of
each color register. As a standard practice, then, for these
and certain other write-only registers, you may wish to keep a
"back-up" or "shadow" copy in RAM. As you write to the color
register itself, you should update this RAM copy. If you do so,
you will always know the value each register contains.