DIRECT MEMORY ACCESS UNIT
10-6
Figure 10-4. Destination-Synchronized Transfers
10.1.5 Internal Requests
Internal DMA requests can come from either Timer 2 or the system software.
10.1.5.1 Timer 2-Initiated Transfers
When programmed for Timer 2-initiated transfers, the DMA channel performs one DMA transfer
every time that Timer 2 reaches its maximum count. Timer-initiated transfers are useful for ser-
vicing time-based peripherals. For example, an A/D converter would require data every 22 mi-
croseconds in order to produce an audio range waveform. In this case, the DMA source would
point to the waveform data, the destination would point to the A/D converter and Timer 2 would
request a transfer every 22 microseconds. (See “Timed DMA Transfers” on page 10-26.)
10.1.5.2 Unsynchronized Transfers
DMA transfers can be initiated directly by the system software by selecting unsynchronized
transfers. Unsynchronized transfers continue, back-to-back, at the full bus bandwidth, until the
channel’s transfer count reaches zero or DMA transfers are suspended by an NMI.
T1
T2
T3
T4
CLKOUT
DRQ
(Case 1)
T1
T2
T3
T4
DRQ
(Case 2)
Fetch Cycle
Deposit Cycle
NOTES:
1. Current destination synchronized transfer will not be immediately
followed by another DMA transfer.
2. Current destination synchronized transfer will be immediately
followed by another DMA transfer.
2
1
TI
TI
A1189-0A
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...
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Страница 80: ...3 Bus Interface Unit...
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Страница 130: ...4 Peripheral Control Block...
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Страница 140: ...5 ClockGenerationand Power Management...
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Страница 166: ...6 Chip Select Unit...
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Страница 190: ...7 Refresh Control Unit...
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Страница 206: ...8 Interrupt Control Unit...
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Страница 239: ...INTERRUPT CONTROL UNIT 8 32...
Страница 240: ...9 Timer Counter Unit...
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Страница 266: ...10 Direct Memory Access Unit...
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Страница 295: ...DIRECT MEMORY ACCESS UNIT 10 28...
Страница 296: ...11 Math Coprocessing...
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Страница 314: ...12 ONCE Mode...
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Страница 318: ...A 80C186 Instruction Set Additions and Extensions...
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Страница 330: ...B Input Synchronization...
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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...
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Страница 408: ...Index...
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