Answer to Question #258966 in Electrical Engineering for SUNNY

Question

Why are the read and write control lines in a DMA controller bidirectional? Under what

condition and for what purpose are they used as inputs? Under what condition and for what

purpose are they used as outputs?

Answer 1

DMA stands for direct memory access. In this the data is directly transferred from memory to I/O devices.We do not need to take CPU into account to transfer data.The read and write buses run through data buses and they have control signals, a bus request is placed by DMA to CPU. DMA does this to take control over CPU. The BUS request is then terminated by CPU, and DMA handles the BUS request.This is done with the help of data bus, control lines and address bus. SO, the read-write control lines are kept Bidirectional. DMA has to run in both direction according to the direction instructed by Bus grant.

When DMA generate a signal to put the input word to data bus, its control lines works as input , when DMA signal indicate to receive data from data bus it works as Output.