Question

it is necessary to transfer 256 words from a magnetic disk to a memory section starting from 1230. the transfer is by means of dma. (1+1=2 marks) a. give the initial values that the cpu must transfer to the dma controller. b. give the step by step account of the actions taken during the input of the first two words.

Answer 1

The steps are as following:-

• When the first word of the magnetic disk is created, it sends a DMA request, the DMA Controller Bus cancels the request so that the CPU is requested to leave the buses.

• The bus receptive CPU responds to the bus issued by the bus issued by the bus.

• The DMA address then sets the current entry address (= 1230) on the bus and sends the DMA receipt to the magnetic disk.

• Then the magnetic disk then puts the first word on the data bus and activates the DMA-written control line which writes to the word memory.

• When a second word is ready for the magnetic disk, it sends the DMA request again.

• The DMA address then sets the current entry address (= 1231) on the bus and accepts the DMA on the magnetic disk.

• Then the second word after the magnetic disk puts data on the bus and activates the DMA-written control line which writes to the word memory.

• Then DMA deactivates written control line, incremental address registration (= 1232) and decreasing word count registration .