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Each of the DMA channels can be independently enabled or disabled. The enable bits are
bits SRCA, SRCB, SRCC, and DEST in control register zero (BLTCON0).
When disabled, no memory cycles will be executed for that channel and, for a source
channel, the constant value stored in the data register of that channel will be used for
each blitter cycle. For this purpose, each of the three source channels have preloadable
data registers, called BLTxDAT.
Images in memory are usually stored in a linear fashion; each word of data on a line is
located at an address that is one greater than the word on its left. i.e. Each line is a "plus
one" continuation of the previous line. (See Figure 6-1.)
20 21 22 23 24 24 26
27 28 29 30 31 32 33
34 35 36 37 38 39 40
41 42 43 44 45 46 47
48 49 50 51 52 53 54
55 56 57 58 59 60 61
Figure 6-1: How Images are Stored in Memory
The map in Figure 6-1 represents a single bit-plane (one bit of color) of an image at word
addresses 20 through 61. Each of these addresses accesses one word (16 pixels) of a
single bitplane. If this image required sixteen colors, four bit-planes like this would be
required in memory, and four copy (move) operations would be required to completely
move the image.
The blitter is very efficient at copying such blocks because it needs to be told only the
starting address (20), the destination address, and the size of the block (height = 6, width
= 7). It will then automatically move the data, one word at a time, whenever the data bus
is available. When the transfer is complete, the blitter will signal the processor with a flag
and an interrupt.
NOTE
This copy (move) operation operates on memory and may or may not change the memory
currently being used for display.
All data copy blits are performed as rectangles of words, with a given width and height. All
four DMA channels use a single blit size register, called BLTSIZE, used for both the width
and height. The width can take a value of from 1 to 64 words (16 to 1024 bits). The
height can run from 1 to 1024 rows. The width is stored in the least significant six bits of
the BLTSIZE register. If a value of zero is stored, a width count of 64 words is used. This
is the only parameter in the blitter
- Blitter Hardware 165 -
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...