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12-3
DMA CONTROLLER
12.1.1 DMA Terminology
This section provides a definition of some of the terms used in this chapter to describe the DMA
controller.
DMA Process A DMA process is the execution of a programmed DMA task from
beginning to end. Each DMA process requires initial programming
by the Intel386 EX processor.
Buffer A contiguous block of data.
Buffer Transfer The action required by the DMA to transfer an entire buffer.
Data Transfer The DMA action in which a group of bytes or words are moved
between devices by the DMA controller. A data transfer operation
may involve movement of one or many bytes.
Bus Cycle Access by the DMA to a single byte or word.
Requester The Requester is the device which requests service by the DMA
controller. All of the control signals which the DMA monitors or
generates for specific channels are logically related to the requester.
Only the requester is considered capable of initiating or terminating a
DMA process. The requester may be either I/O or memory and may
be the Source or the Destination of the transfer or neither.
Target The Target is the device with which the Requester wishes to
communicate. As far as the DMA process is concerned, the Target is
a slave which is incapable of control over the process. The Target
may be either I/O or memory, and may be either the Source or the
Destination of the transfer.
Source The Source is the memory or I/O from which data is being read.
Destination The Destination is the memory or I/O to which data is being written.