While the microprocessor is executing a program an interface circuit takes over control of address, data, control buses when not in use by microprocessor
DMA controller taking over the address, data and control buses while a block of data is transferred between memory and I/O device
The DMA control waiting for the microprocessor to finish execution of the program and then takes over the buses
Data transfer takes place between the I/O device and memory during every alternate clock cycle
EXAMIANS