Question_1: The following codereads port 0x21 (interrupt mask register) of PIC (

Question

Question_1: The following codereads port 0x21 (interrupt mask register) of PIC (ProgrammableInterrupt Controller), sets the 2nd bit that is mapped to IRQ1 andwrites it back to port 0x21. As a result keyboard interrupt will bedisabled as IRQ1 is used bykeyboard.                             

; disable keyboard interrupt in PIC mask register

01        [org 0x0100]

02                   in al, 0x21                ; read interrupt mask register

03                   or al, 2                      ; set bit for IRQ1

04                   out 0x21, al            ; write back mask register

05                   mov ax, 0x4c00      ; terminate program

06                   int 0x21

Modify instruction_03 for the following:

             I.      set bit for IRQ0

          II.      set bit for IRQ6

        III.      set bits for IRQ1, IRQ3 andIRQ4

       IV.      clear bit for IRQ5

          V.      clear bits for IRQ2, IRQ5, IRQ6and IRQ7

Question_2: Suggest a reasonfor thefollowing:                                                                 

             I.      We should disable interrupts whilehooking interrupt 8h, i.e. while placing its segment and offset inthe interrupt vector table.

          II.      We need not do this for interrupt80h.

Explanation / Answer

Dear... Question 1: 1. Set bit to disable IRQ0                               IN AL, 21H                   ; Read interruptmaskregister
                              OR AL , 1                      ; set bit 1                               OUT 20H , AL               ; modify the interrupt mask register 2. Set bit to disable IRQ6                                                IN AL, 21H                   ; Read interruptmaskregister
                               OR AL , 10000000B      ; set bit 6                                OUT 21H , AL               ; modify the interrupt maskregister 2. Set bit to disable IRQ6                                                IN AL, 21H                   ; Read interruptmaskregister
                               OR AL , 10000000B      ; set bit 6                                OUT 21H , AL               ; modify the interrupt maskregister 2. Set bit to disable IRQ6                                                IN AL, 21H                   ; Read interruptmaskregister
                               OR AL , 10000000B      ; set bit 6                                OUT 21H , AL               ; modify the interrupt maskregister                                 4.   Set bit to disableIRQ5                                    IN AL, 21H                   ; Read interruptmaskregister
                              OR AL , 5                      ; set bit 1                               OUT 21H , AL               ; modify the interrupt maskregister Question 2: Inorder to hook any interrupt we need to disable remaininginterrupts.But comming to interrupt 80h as it is a defaultinterrupt handler has the irritating behavior of switching the RealTime Clock interrupt off after a time-out expires i.e doesn't needoffset in the interrupt vector table . Hope this will helpyou..

Related Questions

Navigate

• Browse (All)
• Browse Q
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.