Commodore Amiga A500 Technical Reference Manual page 215

DMA Time Slot
Allocation/Horizontal
Line (Cont`d)
Data fetch start can only be specified at even multiples of 8
clocks. This is the clock position which should be specified for
the normal width display. (20 word fetch for 320 pixel, 40
word fetch for 640 pixel width).
Five clocks must occur before the data which was fetched for a
particular position can appear onscreen. For example, if data
fetch start is specified as 38, it will not be available for display
until clock number 45.
38
1
4 6 2 3
4 2
- 1
48
3
4 6 2 3
4 2 3 1 4 2
3
A hardware data-fetch stop has been installed at count D8 so as
to prevent the bit-plane data-fetch from overrunning the time
allotted for the memory refresh or disk DMA.
00
20
6 3
4 2
38
212
D a t a f e t c h d o n e
f o r c y c l e 3 8
40
2
5 1 4 6 2
3 1 4 2 3 1 4
1 2
3 2 0 m o d e B i t - P l a n e D M A , b y p l a n e
6 4 0 m o d e B i t - P l a n e D M A , b y p l a n e
50
4
5 1 4 6 2
3 1 4 2 3 1 4
5 6
08
21
5 6
1 4 2
39 40
48
3
5 1
( c o n t i n u e s
b e l o w )
2 3 1
3
58
N o r m a l R e s .
C Y C L E S
5 - 1 9 s a m e
a s c y c l e 4
3
5 1
2 3 1
H i g h R e s .
C Y C L E S
8 - 3 7 s a m e
a s c y c l e 7
7
EO
E n d o f
3 5 1
H o r i z o n t a l
L i n e D a t a
F e t c h C y c l e
41