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The blitter can only access CHIP memory - that portion of memory accessible by the
display hardware. Attempting to use the blitter to read or write FAST or other non-CHIP
memory may result in destruction of the contents of CHIP memory.
A "blit" is a single operation of the blitter - perhaps the drawing of a line or movement of
a block of memory. A blit is performed by initializing the blitter registers with appropriate
values and then starting the blitter by writing the BLTSIZE register. As the blitter is an
asynchronous coprocessor, the 68000 continues to run as the blit is executing.
MEMORY LAYOUT
The blitter is a word blitter, not a bit blitter. All data fetched, modified, and written are in
full 16-bit words. Through careful programming, the blitter can do many "bit" type
operations.
The blitter is particularly well suited to graphics operations. As an example, a 320 by 200
screen set up to display 16 colors is organized as four bitplanes of 8,000 bytes each. Each
bitplane consists of 200 rows of 40 bytes or 20 16-bit words. (From here on, a "word" will
mean a 16-bit word.)
DMA CHANNELS
The blitter has four DMA channels - three source channels, labelled A, B, and C, and one
destination channel, called D. Each of these channels has separate address pointer,
modulo and data registers and an enable bit. Two have shift registers, and one has a first
and last word mask register. All four share a single blit size register.
The address pointer registers are each composed of two words, named BLTxPTH and
BLTxPTL. (Here and later, in referring to a register, any "x" in the name should be
replaced by the channel label, A, B, C, or D.) The two words of each register are adjacent
in the 68000 address space, with the high address word first, so they can both be written
with one 32-bit write from the processor. The pointer registers should be written with an
address in bytes. Because the blitter works only on words, the least significant bit of the
address is ignored. Because only CHIP memory is accessible, some of the most significant
bits will be ignored as well. On machines with 512 KB of CHIP memory, the most
significant 13 bits are ignored. Future machines will have more CHIP memory and fewer
bits will be ignored. A valid, even, CHIP memory address should always be written to
these registers.
NOTE
Be sure to write zeros to all unused bits in the custom chip registers. These bits may be
used by later versions of the custom chips. Writing non-zero values to these bits may
cause unexpected results on future machines.
- 164 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...