Figure 3-15 Data Fetch For The First Line When Modulo; Figure 3-16 Data Fetch For The Second Line When Modulo - Commodore Amiga Hardware Reference Manual

Data for Line 1:
Location: START
Leftmost
Display Word
START+2
Next Word
START+4
Next Word
Screen data fetch stops (DDFSTOP) for
each horizontal line after the last word
START+38
Last Display
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 that you intend for that line. The data fetch
for line 2 is shown in figure 3-16.
Data for Line 2:
Location: START+80
Leftmost
Display Word
START+82
Next Word
START+84
Next Word
START+118
Last Display
Word
Figure 3-16: Data Fetch for the Second Line When Modulo
=
40
To display the right half of the big picture, you set up a vertical blanking routine to
start the bit-plane pointers at location START+40 rather than START with the modulo
remaining at 40. The data layout is shown in figures 3-17 and 3-18.
Playfield Hardware 67