ABSTRACT
In the design of a simple computer (ASC), we assumed one input device and one
output device transferring data in and out of the accumulator using a programmed
I=O mode. An actual computer system, however, consists of several input and output devices or peripherals. Although the programmed I=O mode can be used in such an environment, it is slow and may not be suitable, especially when the machine is
used as a real-time processor responding to irregular changes in the external
environment. Consider the example of a processor used to monitor the condition
of a patient in a hospital. Although the majority of its patient data gathering
operations can be performed in a programmed I=O mode, alarming conditions such as abnormal blood pressure or temperature occur irregularly, and detection
of such events requires that the processor be interrupted by the event from its regular
activity. We discuss the general concept of interrupt processing and interrupt-driven
I=O in this chapter. The transfer of information between the processor and a peripheral consists of
the following steps:
These steps can be controlled by the processor or the peripheral or both.
Contingent upon where the transfer control is located, three modes of I=O are possible. They are
