Commodore Amiga - Figure 3-9 Positioning the On-Screen Display

($81, $2C)
~--~----320--------~
200
display window
Starting and stopping positions
,
Visible screen boundaries
Figure 3-9: Positioning the On-screen Display
Setting the Display Window Starting PosiJiion
A horizontal starting position of approximately $81 and a vertical starting position of
approximately
$20 centers the display on most standard television screens. If you select
high-resolution mode (640 pixels horizontally) or interlaced mode (400 lines) the starting
position does not change. The starting position is always interpreted in low-resolution,
non-interlaced mode. In other words, you select a starting position
that represents the
correct coordinates in low-resolution, non-interlaced mode.
The register DIWSTRT (for "Display Window Start") controls the display window start-
ing position. This register contains both the horizontal and vertical components of the
display window starting positions, known respectively as HSTART and VSTART.
The
following example sets DIWSTRT for a basic playfield. You write $20 for VSTART and
$81 for HSTART.
Playfield Hardware
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