Question

Under what condition and for what purposes are dma controller used as inputs

Answer 1

In CPU controller and DMA controller. The write and read control lines are “shared’ between the DMA controller and CPU controller. they all have to be bidirectional .so we can say that both the CPU controller and the DMA controller can control (active) these lines when needed. on the other word also we can say that. These control lines running through the data buses and also having control signals, when a DMA controller places a Bus request input (BR) to CPU and to take the control the  over Buses.