The occurrence of an interrupt fires a number of events both in processor hardware and software. The figure below displays a sequence.
The occurrence of interrupt triggers a number of events, both in processor hardware and in
software. The interrupt-driven I/O operation takes the following steps.
The I/O unit issues an interrupt signal to the processor for the exchange of data between
them.
The processor finishes the execution of the current instruction before responding to the
interrupt.
The processor sends an acknowledgment signal to the device that it issued the interrupt.
The processor transfers its control to the requested routine called “Interrupt Service
Routine (ISR)” by saving the contents of program status word (PSW) and the program
counter (PC).
The processor now loads the PC with the location of the interrupt service routine and fetches the instructions. The result is transferred to the interrupt handler program.
When interrupt processing is completed, the saved register’s value is retrieved from the
stack and restored to the register.
Finally, it restores the PSW and PC values from the stack.
Interrupt priority:
Microcomputers can transfer data to or from an external device using an interrupt through an INTR pin. When a device wants to communicate with the microcomputer, it connects to the INTR pin and makes it high or low depending on a microcomputer. The microcomputer responds by sending a signal via its pin called interrupt acknowledgment INTA.
