An interrupt is a signal to the processor emitted by hardware or software indicating an event that needs immediate attention. Whenever an interrupt occurs, the controller completes the execution of the current instruction and starts the execution of an Interrupt Service Routine (ISR) or Interrupt Handler. ISR tells the processor or controller what to do when the interrupt occurs. The interrupts can be either hardware interrupts or software interrupts.
° Hardware Interrupt
A hardware interrupt is an electronic alerting signal sent to the processor from an external device, like a disk controller or an external peripheral. For example, when we press a key on the keyboard or move the mouse, they trigger hardware interrupts which cause the processor to read the keystroke or mouse position.
° Software Interrupt
A software interrupt is caused either by an exceptional condition or a special instruction in the instruction set which causes an interrupt when it is executed by the processor. For example, if the processor's arithmetic logic unit runs a command to divide a number by zero, to cause a divide-by-zero exception, thus causing the computer to abandon the calculation or display an error message. Software interrupt instructions work similar to subroutine calls.
°The state of continuous monitoring is known as polling. The microcontroller keeps checking the status of other devices; and while doing so, it does no other operation and consumes all its processing time for monitoring. This problem can be addressed by using interrupts.
°In the interrupt method, the controller responds only when an interruption occurs. Thus, the controller is not required to regularly monitor the status (flags, signals etc.) of interfaced and inbuilt devices.
