Commodore Amiga A1000, Hardware Reference Manual

Page: 78 / 380

START START+78
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| Width of the Bit-Plane Defined in RAM |
| | |
| Width of defined | |
| screen on which | |
| bit-plane data is | |
| to appear | |
| | |
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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.
Data for Line 1:
Location: START START+2 START+4 .....START+38
Leftmost Next Word Next Word Last Display
Display Word Word
^
Screen data fetch stops (DDFSTOP) for |
each horizontal line after the last word -----------------------|
on the line has been fetched.
Figure 3-15: Data Fetch for the First Line When Modulo = 40
At this point, BPLxPTH and BPLxPTL contain the value START+40. The modulo, which is
40, is added to the current value of the pointer so that when it begins the data fetch for
the next line, it fetches the data you intend for that line. The data fetch for line 2 is shown
in Figure 3-16.
- Playfield Hardware 69 -