Write down the lines of in-line assembly code that load the vector for the Port

Question

Write down the lines of in-line assembly code that load the vector for the Port H Interrupt into the vector table. The name given of the interrupt service routine is Keypad_handler

Explanation / Answer

; OUTINT.ASM ; Forever Young Software ; Copyright 1997 ; All rights reserved ; Version 1.00b .model tiny .186 org 100h start: jmp short InstallIt ;******************************************************************* ;;;; our interrupt code and data goes here .algnw ; lets align it on the next word boundary OurStart: cli push ds ; save data seg push cs ; point ds to cs pop ds or ah,ah ; if ah = 0 then service 0 je short Service0 cmp ah,01 ; if ah = 1 then service 1 je short Service1 cmp ah,02 ; if ah = 2 then service 2 je short Service2 JustExit: pop ds ; else just return sti iret ; our service #0 (ah = 00h) Service0: mov dx,00h ; do something simple for example jmp short JustExit ; our service #1 (ah = 01h) Service1: mov dx,01h ; do something simple for example jmp short JustExit ; our service #2 (ah = 02h) Service2: mov dx,02h ; do something simple for example jmp short JustExit ; other services go here OurEnd: ;;;; end of our interrupt code and data ;******************************************************************* InstallIt: mov si,offset StartIt ; display start up string call prtstring ; xor bx,bx ; make es:bx point to 0000:00D0h mov es,bx ; mov bx,00D0h ; mov cx,204 ; 256 interrupts (00-FF)(-34h) MainLoop: mov si,es:[bx] ; get interrupt vector address inc bx ; offset first (little endian) inc bx ; mov ax,es:[bx] ; segment second (little endian) inc bx ; inc bx ; cmp ax,0F000h ; if segment => F000h then in ROM-BIOS jae short NotIRET ; (if in BIOS then skip it) push es ; mov es,ax ; see if IRET mov dl,es:[si] ; pop es ; cmp dl,0CFh ; is it IRET je short FndOne ; if so, then not used NotIRET: inc byte CIntVNum ; inc for next time loop MainLoop ; mov si,offset NoFndOneS ; didn't find one call prtstring jmp short DoneErr FndOne: mov si,offset FndOneS call prtstring mov ax,bx sub ax,04 ; backup to first of vector call prthex mov si,offset IntNumS call prtstring mov al,CIntVNum ; display current int number call prthexs ; mov dl,'h' ; print 'h' mov ah,02 ; int 21h ; push cs pop ds mov al,CIntVNum ; vector to change mov ah,25h mov dx,offset cs:OurStart int 21h mov ah,62h ; get and free environment block int 21h ; mov es,bx ; mov ax,es:[2Ch] ; mov es,ax ; mov ah,49h ; int 21h ; mov dx,offset cs:OurEnd ; offset of end of our code shr dx,04 ; div by 16 (make it a paragraph #) inc dx ; just in case add dx,16 ; The PSP mov ax,3100h ; service number and RC = 0 int 21h ; TSR service DoneErr: mov ah,4Ch ; exit to DOS (no TSR) int 21h ; prtstring proc near uses ax dx si ps1: mov dl,[si] ; Get character inc si ; Point to next one or dl,dl ; End of string? jz short ps2 ; Yes, so exit mov ah,02h ; Output a character int 21h jmp short ps1 ; Keep doing it ps2: ret prtstring endp PrtHexs proc near uses ax bx dx cx mov bx,offset Hex push ax shr al,04h xlatb mov dl,al mov ah,02 int 21h pop ax and al,0Fh xlatb mov dl,al mov ah,02 int 21h ret PrtHexs endp PrtHex proc near uses ax bx cx dx mov bx,offset Hex mov cx,04h HexLoop: push ax mov al,ah shr al,04h xlatb mov dl,al mov ah,02 int 21h pop ax shl ax,04h loop HexLoop ret PrtHex endp CIntVNum db 34h ; starting with int 34h StartIt db 13,10,'Interrupt Install Util Version 01.00b' db 13,10,'Forever Young Software(r) (C)opyright 1984-2000',13,10 db 13,10,' Finding unused Interrupt vector number... (starting with 34h)',13,10,0 NoFndOneS db 13,10,"****Didn't find an unused interrupt vector number***" FndOneS db 13,10,' Found an unused interrupt at: 0000:',0 IntNumS db 13,10,' Interrupt number: ',0 Hex db '0123456789ABCDEF' .end start

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