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The raw MFM data that must be presented to the disk controller will be twice as large as
the unencoded data. The following Table shows the relationship:
1 ---> 01
0 ---> 10 ;if following a 0
0 ---> 00 ;if following a 1
With clever manipulation, the blitter can be used to encode and decode the MFM.
In one common form of GCR recording, each data byte always has the most significant bit
set to a 1. MSBSYNC, when a 1, tells the disk controller to look for this sync bit on every
disk byte. When reading a GCR formatted disk, the software must use a translate Table
called a nybbleizer to assure that data written to the disk does not have too many
consecutive 1's or 0's.
DSKSYNC - DISK INPUT SYNCHRONIZER
The DSKSYNC register is used to synchronize the input stream. This is highly useful when
reading disks. If the WORDSYNC bit is enabled in ADKCON, no data is transferred until a
word is found in the input stream that matches the word in the DSKSYNC register. On
read, DMA will start with the following word from the disk. During disk read DMA, the
controller will resync every time the word match is found. Typically the DSKSYNC will be
set to the magic MFM sync mark value, $4489.
In addition, the DSKSYNC bit in INTREQ is set when the input stream matches the
DSKSYNC register. The DSKSYNC bit in INTREQ is independent of the WORDSYNC enable.
DISK INTERRUPTS
The disk controller can issue three kinds of interrupts:
o DSKSYNC (level 5, INTREQ bit 12) - input stream matches the DSKSYNC register.
o DSKBLK (level 1, INTREQ bit l) - disk DMA has completed.
o INDEX (level 6, 8520 Flag pin) - index sensor triggered.
Interrupts are explained further in the section "Length, Direction, DMA Enable". See
Chapter 7, "System Control Hardware," for more information about interrupts. See
Appendix F for more information on the 8520.
- 244 Interface 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...