DIRECT MEMORY ACCESS UNIT
10-20
10.2.2 Suspension of DMA Transfers
Whenever the CPU receives an NMI, all DMA activity is suspended at the end of the current
transfer. The CPU suspends DMA activity by setting the DHLT bit in the Interrupt Status Regis-
ter (Figure 8-14 on page 8-23). When an IRET instruction is executed, the CPU clears the DHLT
bit and DMA transfers are allowed to resume. Software can read and write the DHLT bit.
NOTE
Do not write to the DHLT bit while Timer/Counter Unit interrupts are enabled.
A conflict with the internal use of the register may cause incorrect processing
of timer interrupts.
The DHLT bit does not function when the interrupt controller is in slave mode.
10.2.3 Initializing the DMA Unit
Use the following sequence when programming the DMA Unit:
1.
Program the source and destination pointers for all used channels.
2.
Program the DMA Control Registers in order of highest-priority channel to lowest-
priority channel.
10.3 HARDWARE CONSIDERATIONS AND THE DMA UNIT
This section covers hardware interfacing and performance factors for the DMA Unit.
10.3.1 DRQ Pin Timing Requirements
The DRQ pins are sampled on the falling edge of CLKOUT. The DRQ pins must be set up a min-
imum of T
INVCL
before CLKOUT falling, to guarantee recognition at a specific clock edge. Refer
to the data sheet for specific values.
The DRQ pins have an internal synchronizer. Violating the setup time can cause only a missed
DMA request, not a processor malfunction.
Содержание 80C186XL
Страница 1: ...80C186XL 80C188XL Microprocessor User s Manual...
Страница 2: ...80C186XL 80C188XL Microprocessor User s Manual 1995...
Страница 18: ...1 Introduction...
Страница 19: ......
Страница 27: ......
Страница 28: ...2 Overview of the 80C186 Family Architecture...
Страница 29: ......
Страница 79: ......
Страница 80: ...3 Bus Interface Unit...
Страница 81: ......
Страница 127: ......
Страница 128: ...4 Peripheral Control Block...
Страница 129: ......
Страница 137: ......
Страница 138: ...5 ClockGenerationand Power Management...
Страница 139: ......
Страница 154: ...6 Chip Select Unit...
Страница 155: ......
Страница 178: ...7 Refresh Control Unit...
Страница 179: ......
Страница 193: ......
Страница 194: ...8 Interrupt Control Unit...
Страница 195: ......
Страница 227: ......
Страница 228: ...9 Timer Counter Unit...
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Страница 253: ......
Страница 254: ...10 Direct Memory Access Unit...
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Страница 284: ...11 Math Coprocessing...
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Страница 302: ...12 ONCE Mode...
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Страница 306: ...A 80C186 Instruction Set Additions and Extensions...
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Страница 318: ...B Input Synchronization...
Страница 319: ......
Страница 322: ...C Instruction Set Descriptions...
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Страница 371: ......
Страница 372: ...D Instruction Set Opcodes and Clock Cycles...
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Страница 396: ...Index...
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