The DMA controller acts as a bridge between the bus and the input/output devices. Despite the fact that it conveys data without the intervention of the processor, it is controlled by the processor. The CPU starts the DMA controller by transmitting the beginning address, the number of words in the data block, and the data transfer direction. Specifically, from I/O devices to memory or from main memory to I/O devices. The DMA controller can be linked to more than one external device.
The DMA controller has an address unit that generates addresses and selects I/O devices for transmission. It also includes a control unit and a data count for keeping track of the number of blocks transported and identifying the direction of data transfer. When the transfer is finished, DMA sends an interrupt to the CPU.
The CPU is idle during DMA and has no influence over the memory buses. The DMA controller takes over the buses to manage direct transfers between I/O devices and memory units. The data is sent after the DMA has assumed control of the buses. This transfer can occur in a variety of ways.
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