Sample data for 4 pixels
a b c d
1 1 0 0 Data in Bit-Plane 5 Most Significant
1 0 1 0 Data in Bit-Plane 4
1 0 0 1 Data in Bit-Plane 3
0 1 1 1 Data in Bit-Plane 2
0 0 1 0 Data in Bit-Plane 1 Least Significant
a Value 6 COLOR 6
b Value 11 COLOR 11
c Value 18 COLOR 18
d Value 28 COLOR 28
Figure 34: Significance of Bit-Plane Data in Selecting Colors
You also have the choice of defining two separate playfields, each formed from up to three
bit planes. Each of the two playfields uses a separate set of eight different colors. This is
called dual-playfield mode.
FORMING A BASIC PLAYFIELD
To get you started, this section describes how to directly access hardware registers to
form a single basic playfield that is the same size as the video screen. Here, "same size"
means that the playfield is the same size as the actual display window. This will leave a
small border between the playfield and the edge of the video screen. The playfield usually
does not extend all the way to the edge of the physical display.
To form a playfield, you need to define these characteristics:
o Height and width of the playfield and size of the display window (that is, how much of
the playfield actually appears on the screen).
o Color of each pixel in the playfield.
o Horizontal resolution.
- 38 Playfield Hardware -
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