10-9
DIRECT MEMORY ACCESS UNIT
The last point is extremely important when the two channels use different synchronization. For
example, consider the case in which channel 1 is programmed for high priority and destination
synchronization and channel 0 is programmed for low priority and source synchronization. If a
DMA request occurs for both channels simultaneously, channel 1 performs the first transfer. At
the end of channel 1’s deposit cycle, two idle states are inserted (thus releasing the bus). With the
bus released, channel 0 is free to perform its transfer even though the higher-priority channel
has not completed all of its transfers. Channel 1 regains the bus at the end of channel 0’s trans-
fer. The transfers will alternate as long as both requests remain active.
Figure 10-5. Two-Channel DMA Module
A higher-priority DMA channel will interrupt the transfers of a lower-priority channel. Figure
10-6 shows several transfers with different combinations of channel priority and synchronization.
Internal - DMA
Request
Multiplexer
Inter-module
Arbitration
Logic
Channel 1
Control Logic
DRQ Pin
DRQ Pin
Channel 0
Control Logic
Destination Pointer
Source Pointer
Destination Pointer
Source Pointer
Module
DMA Request
Timer 2
Timer 2
Request
Timer 2 Request
A1540-01
Содержание 80C186EA
Страница 1: ...80C186EA 80C188EA Microprocessor User s Manual...
Страница 2: ...80C186EA 80C188EA Microprocessor User s Manual 1995...
Страница 19: ......
Страница 20: ...1 Introduction...
Страница 21: ......
Страница 28: ...2 Overview of the 80C186 Family Architecture...
Страница 29: ......
Страница 79: ......
Страница 80: ...3 Bus Interface Unit...
Страница 81: ......
Страница 129: ......
Страница 130: ...4 Peripheral Control Block...
Страница 131: ......
Страница 139: ......
Страница 140: ...5 ClockGenerationand Power Management...
Страница 141: ......
Страница 165: ......
Страница 166: ...6 Chip Select Unit...
Страница 167: ......
Страница 190: ...7 Refresh Control Unit...
Страница 191: ......
Страница 205: ......
Страница 206: ...8 Interrupt Control Unit...
Страница 207: ......
Страница 239: ...INTERRUPT CONTROL UNIT 8 32...
Страница 240: ...9 Timer Counter Unit...
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Страница 265: ......
Страница 266: ...10 Direct Memory Access Unit...
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Страница 295: ...DIRECT MEMORY ACCESS UNIT 10 28...
Страница 296: ...11 Math Coprocessing...
Страница 297: ......
Страница 314: ...12 ONCE Mode...
Страница 315: ......
Страница 318: ...A 80C186 Instruction Set Additions and Extensions...
Страница 319: ......
Страница 330: ...B Input Synchronization...
Страница 331: ......
Страница 334: ...C Instruction Set Descriptions...
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Страница 383: ...INSTRUCTION SET DESCRIPTIONS C 48...
Страница 384: ...D Instruction Set Opcodes and Clock Cycles...
Страница 385: ......
Страница 408: ...Index...
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