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--------1.CPU tells DMA controller: Read/Write,Device address,Starting address of memory block for data,Amount of data to be transferred
--------2.CPU carries on with other work
--------3.DMA controller deals with transfer and takes over bus for a cycle
--------4.DMA controller sends interrupt when finished
DMA helps in directly accessing memory without burdening the processor. DMA will take care of all read/write transfers to/from memory.
The communication between processor and DMA can be based on any protocol like request-grant technique. DMA controllers usually have multiple output banks/ports which support many no of memory. if u r new to DMA the data sheet of INTEL 8237 DMA controller shall be a good starting point.