What are the control methods for data transmission of external devices? What are their advantages and disadvantages?

The transmission modes of data control are: (1) program direct control mode.

Advantages: Although the program direct control mode is relatively simple, it does not need much hardware support.

Disadvantages: ①CPU utilization is low. ② The utilization rate of peripherals is low, and peripherals can't work in parallel.

⑵ Interrupt control mode

Advantages: the utilization rate of CPU is greatly improved, and it can support parallel operation between peripherals, avoiding the work of CPU cycle test control status register.

Disadvantages: When each device inputs and outputs data, the number of times to interrupt the CPU will also increase, which will greatly reduce the effective calculation time of the CPU.

(3) DMA mode is also called direct memory access mode.

Advantages: it reduces the intervention of CPU in I/O control, further improves the use efficiency of CPU, and also improves the degree of parallel operation between CPU and I/O equipment.

Disadvantages: ① management of peripherals and ① some operations in ①DMA mode are still controlled by CPU; ② Using multiple DMA controllers at the same time may lead to the conflict of memory addresses, which is also uneconomical.