Figure 6.5: Changes of memory and register for an interrupt

Interrupt Processing:

• An interrupt occurs when the processor is executing the instruction of location N.


• At that point, the value of program counter is N+1 .


• Processor services the interrupt after completion of current instruction execution.


• First, it moves the content of general registers to system stack.


• Then it moves the program counter value to the system stack.


• Top of the system stack is maintained by stack pointer.


• The value of stack pointer is modified to point to the top of the stack.


• If M elsments are moved to the system stack, the value of stack pointer is changed from T to T-M.