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FUNCTION GENERATOR
The blitter can combine the data from the three source DMA channels in up to 256
different ways to generate the values stored by the destination DMA channel. These
sources might be one bitplane from each of three separate graphics images. While each of
these sources is a rectangular region composed of many points, the same logic operation
will be performed on each point throughout the rectangular region. Thus, for purposes of
defining the blitter logic operation it is only necessary to consider what happens for all of
the possible combinations of one bit from each of the three sources.
There are eight possible combinations of values of the three bits, for each of which we
need to specify the corresponding destination bit as a zero or one. This can be visualized
with a standard truth Table, as shown below. We have listed the three source channels,
and the possible values for a single bit from each one.
A B C D BLTCON0 position MINTERM
___
0 0 0 ? 0 ABC
__
0 0 1 ? 1 ABC
_ _
0 1 0 ? 2 ABC
_
0 1 1 ? 3 ABC
__
1 0 0 ? 4 ABC
_
1 0 1 ? 5 ABC
_
1 1 0 ? 6 ABC
1 1 1 ? 7 ABC
This information is collected in a standard format, the LF control byte in the BLTCON0
register. This byte programs the blitter to perform one of the 256 possible logic operations
on three sources for a given blit.
To calculate the LF control byte in BLTCON0, fill in the truth Table with desired values for
D, and read the function value from the bottom of the Table up.
For example, if we wanted to set all bits in the destination where the corresponding A
source bit is 1 or the corresponding B source bit is 1, we would fill in the last four entries
of the truth Table with 1 (because the A bit is set) and the third, fourth, seven, and eight
entries with 1 (because the B bit is set), and all others (the first and second) with 0,
because neither A nor B is set. Then, we read the truth Table from the bottom up, reading
11111100, or $FC.
- "$" indicates hex notation.
- 168 Blitter 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...