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"OUT-OF-SYNC" CONDITION
Noise or other glitches may cause the keyboard to get out of sync with the computer. This
means that the keyboard is finished transmitting a code, but the computer is somewhere
in the middle of receiving it.
If this happens, the keyboard will not receive its handshake pulse at the end of its
transmission. If the handshake pulse does not arrive within 143 ms of the last clock of the
transmission, the keyboard will assume that the computer is still waiting for the rest of
the transmission and is therefore out of sync. The keyboard will then attempt to restore
sync by going into "resync mode." In this mode, the keyboard clocks out a 1 and waits for
a handshake pulse. If none arrives within 143 ms, it clocks out another 1 and waits again.
This process will continue until a handshake pulse arrives.
Once sync is restored, the keyboard will have clocked a garbage character into the
computer. That is why the key-up/key-down flag is always transmitted last. Since the
keyboard clocks out 1's to restore sync, the garbage character thus transmitted will
appear as a key release, which is less dangerous than a key hit.
Whenever the keyboard detects that it has lost sync, it will assume that the computer
failed to receive the keycode that it had been trying to transmit. Since the computer is
unable to detect lost sync, it is the keyboard's responsibility to inform the computer of the
disaster. It does this by transmitting a "lost sync" code (value $F9 = 11111001) to the
computer. Then it retransmits the code that had been garbled.
NOTE
The only reason to transmit the "lost sync" code to the computer is to alert the software
that something may be screwed up. The "lost sync" code does not help the recovery
process, because the garbage keycode can't be deleted, and the correct key code could
simply be retransmitted without telling the computer that there was an error in the
previous one.
POWER-UP SEQUENCE
There are two possible ways for the keyboard to be powered up under normal
circumstances: <1> the computer can be turned on with the keyboard plugged in, or <2>
the keyboard can be plugged into an already "on" computer. The keyboard and computer
must handle either case without causing any upset.
- 346 Appendix H -
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...