Which of the following is the correct sequence with regard to service routine?

A. Save contents of processor registers

B. Turn the interrupt facility on

C. Service the device whose flag is set

D. Check which flag is set

E. Restore contents of processor registers

Choose the correct answer from the options given below:

The correct answer is Option 4.

Key Points

• To understand the correct sequence of a service routine, it is essential to follow the logical order of operations when handling an interrupt:
  • Save contents of processor registers (A): This ensures that the current state of the processor is preserved, so it can be restored later.
  • Check which flag is set (D): Determine which device or event caused the interrupt.
  • Service the device whose flag is set (C): Perform the necessary actions to handle the interrupt.
  • Restore contents of processor registers (E): Restore the processor to its previous state.
  • Turn the interrupt facility on (B): Re-enable interrupts to allow further interrupt handling.

The correct sequence is: A, D, C, E, B.

Additional Information

• This sequence ensures that the system correctly handles the interrupt without losing any critical information or causing inconsistencies.
• Each step is crucial for maintaining the integrity of the processor state and ensuring that the system can continue to operate correctly after the interrupt is serviced.