
comparison.) The line number will never be greater than $FF The horizontal position has a
maximum value of $E2. This means that the largest number that will ever appear in the
comparison is $FFE2. When waiting for $FFE2, the line $FF will be reached, but the
horizontal position $FE will never happen. Thus, the position will never reach $FFFE.
You may be tempted to wait for horizontal position $FE (since it will never happen), and
put a smaller number into the vertical position field. This will not lead to the desired
result. The comparison operation is waiting for the beam position to become greater than
or equal to the entered position. If the vertical position is not $FF, then as soon as
the line number becomes higher than he entered number, the comparison will evaluate to
true and the wait will end.
The following notes on horizontal and vertical beam position apply to both the WAIT
instruction and o the SKIP instruction. The SKIP instruction is described below in the
"Advanced Topics" section.
HORIZONTAL BEAM POSITION
The horizontal beam position has a value of $0 to $E2. The least significant bit is not used
in the comparison, so there are 113 positions available for Copper operations. This
corresponds to 4 pixels in low resolution and 8 pixels in high resolution. Horizontal
blanking falls in the range of $0F to $35. The standard screen (320 pixels wide) has an
unused horizontal portion of $04 to $47 (during which only the background color is
displayed).
All lines are not the same length in NTSC. Every other line is a long line (228 color clocks,
0-$E3), with the others being 227 color clocks long. In PAL, they are all 227 long. The
display sees all these lines as 227 1/2 color clocks long, while the copper sees alternating
long & short lines.
VERTICAL BEAM POSITION
The vertical beam position can be resolved to one line, with a maximum value of 255.
There are actually 262 NTSC (312 PAL) possible vertical positions. Some minor
complications can occur if you want something to happen within these last six or seven
scan lines. Because there are only eight bits of resolution for vertical beam position
(allowing 256 different positions), one of the simplest ways to handle this is shown below.
- 18 Coprocessor Hardware -
Содержание Amiga A1000
Страница 1: ...AMIGA HARDWARE REFERENCE MANUAL 1992 Commodore Business Machines Amiga 1200 PAL...
Страница 20: ...Figure 1 1 Block Diagram for the Amiga Computer Family Introduction 11...
Страница 21: ...12 Introduction...
Страница 72: ...Figure 3 12 A dual Playfield display Playfield Hardware 63...
Страница 87: ...Figure 3 24 Horizontal Scrolling 78 playfield hardware...
Страница 101: ...92 Playfield Hardware...
Страница 199: ...Figure 6 9 DMA time slot allocation 190 Blitter hardware...
Страница 203: ...Figure 6 13 Blitter Block Diagram 194 Blitter Hardware...
Страница 229: ...220 System Control Hardware...
Страница 246: ...Figure 8 8 Chinon Timing diagram cont Interface Hardware 237...
Страница 265: ...256 Interface Hardware...
Страница 289: ...280 Appendix A...
Страница 297: ...288 Appendix B...
Страница 298: ...APPENDIX C CUSTOM CHIP PIN ALLOCATION LIST NOTE Means an active low signal Appendix C 289...
Страница 302: ...APPENDIX D SYSTEM MEMORY MAP Appendix D 293...
Страница 343: ...334 Appendix F...
Страница 351: ...342 Appendix G...
Страница 361: ...352 Appendix H...
Страница 367: ...358 Appendix I...