Question

What is a limitation of using DMA transfer for slow periodic data, such as a serial line?

Answer 1

What is DMA?

Direct Memory Access

When peripherals directly communicate with memory using the system bus, without the intervention of the CPU it is known as DMA or direct memory access. During DMA the CPU is idle and it has no control. The transfer is directly between IO device and memory. Since memory process data at very high speed (in GHz) it is absolutely necessary that IO device work at fast speed like magnetic disk.

LImitation of DMA

CPU puts all its lines at high impedance state so that the DMA controller can then transfer data directly between device and memory without CPU intervention. Clearly, it is more suitable for devices with high data transfer rates like disk.

Data is transferred over the serial interface one bit at a time which makes it slow to use DMA.