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详细说明： Overview In computer-based data acquisition applications, data incoming or outgoing through computer I/O devices must often be managed at high speeds or in large quantities. The three primary data transfer mechanisms for computer-based data acquisition are poll ing, interrupts (also known as programmed I/O), and direct memory access (DMA). Polling is a form of foreground data acquisition in which the processor is dedicated to acquiring the incoming data, often by waiting in a loop. The main program calls an acquisition subroutine that waits until the processor collects the required data. With interrupts, the processor is periodically interrupted from executing the main program to store incoming data in a buffer for later retrieval and processing. Interrupts are a form of background acquisition because the main program contains no code that reads data from the input device. Instead, the processor is invisibly stolen periodically from the main program to perform this function. With DMA, a dedicated data transfer device reads incoming data from a device and stores that data in a system memory buffer for later retrieval by the processor. This DMA process occurs transparently from the processor's point of view. ...展开收缩
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