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. TINVCL : 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
T1 or
TW or
TI
T2 or
TW or
TI
T3 or
TW or
TI
T4 or
TI
T1
of
DMA
Cycle
1
A1528-0A
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...
Страница 229: ......
Страница 253: ......
Страница 254: ...10 Direct Memory Access Unit...
Страница 255: ......
Страница 283: ......
Страница 284: ...11 Math Coprocessing...
Страница 285: ......
Страница 302: ...12 ONCE Mode...
Страница 303: ......
Страница 306: ...A 80C186 Instruction Set Additions and Extensions...
Страница 307: ......
Страница 318: ...B Input Synchronization...
Страница 319: ......
Страница 322: ...C Instruction Set Descriptions...
Страница 323: ......
Страница 371: ......
Страница 372: ...D Instruction Set Opcodes and Clock Cycles...
Страница 373: ......
Страница 396: ...Index...
Страница 397: ......