; disable keyboard interrupt in PIC mask register 01 [org 0x0100] 02 in al, 0x21
ID: 3612236 • Letter: #
Question
; 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
I need more help in part III IV and V.
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 answer for
Question 1:
IN AL, 21H ; Read interrupt mask register
OR AL , 1 ; set bit 1
OUT 20H, AL ; modify the interrupt mask register
IN AL, 21H ; Read interrupt mask register
OR AL , 10000000B ; set bit 6
OUT 21H, AL ; modify the interrupt mask register
IN AL, 21H ; Read interrupt mask register
OR AL , 5 ; set bit 1
OUT 21H, AL ; modify the interrupt mask register
And answer 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 that will better answer for u
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