Necessity of Interrupts

Necessity of Interrupts

When you have one or more I/O devices connected to a microprocessor system, any one of them may demand service at any time. The microprocessor can service these devices in one of the two ways. One way is to use the polling routine. The other way is to use an interrupt. In the following section, we will see both ways.

In polling, the microprocessor's software simply checks each of the I/O devices every so often. During this check, the microprocessor tests to see if any device needs servicing.

A more desirable method would be the one that allows the microprocessor to be executing its main program and only stop to service I/O devices when it is told to do so by the device itself. In effect, the method, would provide an external asynchronous input that would inform the processor that it should complete whatever instruction that is currently being executed and fetch a new routine that will service the requesting device. Once this servicing is completed, the processor would resume exactly where it left off. This method is called interrupt method.

Review Questions

1. What are interrupts ?

2.  Explain the term polling with suitable example.