Question

To complete a DMA transfer, a memory to memory transfer requires

(a) a read from memory cycle

(b) a write to memory cycle

(c) a read-from and write-to memory cycle

(d) none of the mentioned

I had been asked this question in final exam.

This intriguing question comes from Programmable DMA Interface 8237 -2 in chapter DMA, Floppy Disk and CRT Controllers of Microprocessor

Answer 1

The correct choice is (c) a read-from and write-to memory cycle

Easiest explanation: A memory to memory transfer is a two cycle operation and requires a read from and write-to memory cycle, to complete each DMA transfer.