DIRECT MEMORY ACCESS UNIT
10-4
10.1.4 External Requests
External DMA requests are asserted on the DRQ pins. The DRQ pins are sampled on the falling
edge of CLKOUT. It takes a minimum of four clocks before the DMA cycle is initiated by the
BIU (see Figure 10-2). The DMA request is cleared four clocks before the end of the DMA cycle
(effectively re-arming the DRQ input).
Figure 10-2. DMA Request Minimum Response Time
External requests (and the resulting DMA transfer) are classified as either source-synchronized
or destination-synchronized. A source-synchronized request originates from the peripheral that is
sending data. For example, a disk controller in the process of reading data from a disk would use
a source-synchronized request (data would be moving from the disk to memory). A destination-
synchronized request originates from the peripheral that is receiving data. If a disk controller
were writing data to a disk, it would use a destination-synchronized request (data would be mov-
ing from memory to the disk). The type of synchronization a channel uses is programmable. (See
“Selecting Channel Synchronization” on page 10-18.)
DRQ
NOTES:
1. T
CLIS
: DMA request to clock low.
2. Synchronizer resolution time.
3. DMA unit priority arbitration and overhead.
4. Bus interface unit latches DMA request and decides to run DMA cycle.
4
2
3
T4
or T3
or T2
or T1
or TW
or TI
T4
or T3
or T2
or T1
or TI
T4
or T3
or TW
or TI
T4
or TI
T1
of
DMA
Cycle
1
A1187-0A
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...
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...
Страница 241: ......
Страница 265: ......
Страница 266: ...10 Direct Memory Access Unit...
Страница 267: ......
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...
Страница 335: ......
Страница 383: ...INSTRUCTION SET DESCRIPTIONS C 48...
Страница 384: ...D Instruction Set Opcodes and Clock Cycles...
Страница 385: ......
Страница 408: ...Index...
Страница 409: ......