Q. Explain Processing of an Interrupt?

The interrupt is processed as:

Step 1:Number field in INT instruction is multiplied by 4 to get its entry in interrupt vector table. For instance the IVT entry for instruction INT 10h willbe found at IVT at an address 40h. In the same way entry of INT 3h will be placed at 0Ch.

Step 2: CPU locates interrupt servicing routine (ISR) whose address is storedat IVT entry of interrupt. For instance in the figure above ISR of INT10h is stored at location at a segment address F000h and an offset F065h.

Step 3: CPU loads IP CS register and IP register with this new address in IVT and transfers control to that address same as a far CALL.

Step 4: IRET (interrupt return) causes program to recommence execution at the subsequent instruction in calling program.