Suppose a program is running on a non-pipelined single processor computer system. The computer is connected to an external device that can interrupt the processor asynchronously. The processor needs to execute the interrupt service routine (ISR) to serve this interrupt. The following steps (not necessarily in order) are taken by the processor when the interrupt arrives: (i) The processor saves the content of the program counter. (ii) The program counter is loaded with the start address of the ISR. (iii) The processor finishes the present instruction. Which ONE of the following is the CORRECT sequence of steps?

When an asynchronous interrupt request is received by a non-pipelined processor during the execution of a program, the processor handles it in the following sequence:

1. Step (iii): The processor checks for interrupts at the end of the current instruction cycle and allows the currently executing instruction to complete.

2. Step (i): To enable resuming execution of the interrupted program later, the return address (the updated content of the Program Counter, along with processor status flags) is saved onto the stack.

3. Step (ii): The Program Counter (PC) is updated with the starting address of the Interrupt Service Routine (ISR) to begin fetching and executing ISR instructions.

Therefore, the correct chronological sequence is (iii), (i), (ii), which corresponds to option (A).

*(Note: Options C and D continue onto the next page and are omitted due to page cut-off.)*