Скачать или смотреть Programmed Input/output transfer [EC 504 CSO] prof. Shruti Dixit

Programmable I/O is one of the I/O technique other than the interrupt-driven I/O and direct memory access (DMA). The programmed I/O was the most simple type of I/O technique for the exchanges of data or any types of communication between the processor and the external devices. With programmed I/O, data are exchanged between the processor and the I/O module. The processor executes a program that gives it direct control of the I/O operation, including sensing device status, sending a read or write command, and transferring the data. When the processor issues a command to the I/O module, it must wait until the I/O operation is complete. If the processor is faster than the I/O module, this is wasteful of processor time. The overall operation of the programmed I/O can be summaries as follow:

The processor is executing a program and encounters an instruction relating to I/O operation.
The processor then executes that instruction by issuing a command to the appropriate I/O module.
The I/O module will perform the requested action based on the I/O command issued by the processor (READ/WRITE) and set the appropriate bits in the I/O status register.
The processor will periodically check the status of the I/O module until it find that the operation is complete.