Figure 3-14 Memory Picture Larger Than The Display - Commodore Amiga Hardware Reference Manual

o If the big picture in memory is larger than the display window, you must
respecify the modulos. The modulo must be some value other than O.
o You must allocate more memory for the larger memory picture.
Specifying the Modulo
For a memory picture wider than the display window, you need to respecify the modulo
so that the correct data words are fetched for each line of the display. As an example,
assume the display window is the standard 320 pixels wide, so 40 bytes are to be
displayed on each line. The big picture in memory, however, is exactly twice as wide as
the display window, or 80 bytes wide. Also, assume that you wish to display the left
half of the big picture. Figure 3-14 shows the relationship between the big picture and
the picture to be displayed.
START
I
Width of the Bit-Plane Defined in RAM
Width of defined
• screen on which
bit-plane data is
to appear
START+78
Figure 3-14: Memory Picture Larger than the Display
Because 40 bytes are to be fetched for each line, the data fetch for line 1 is as shown in
figure 3-15.
66 Playfield Hardware