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TITLE Mod_Vekt.ASM

;==== Programmet laddar 0000:03d0 med koden f”r IRET (CF)
;==== D„refter laddas vektorn f”r INT 1Ch om fr†n default-v„rdet
;==== F000:FF53 till 0000:03D0 via INT 21h/25h
;==== OBS Innan anropet m†ste DS:DX inneh†lla nya SEGMENT-OFFSET-
;==== adressen
;----------------------------------------------------------------------

CSEG    SEGMENT
        ASSUME CS:CSEG, DS:CSEG

        ORG 100H

Start:  jmp     begin
;----------------------------------------------------------------------
;===== Koden f”r IRET skrives in p† adress 0000:03d0

Skriv_IRET PROC NEAR

        push es

        mov ax,0000h                    ;Peka p† segment 0000
        mov es,ax
        mov bx,03d0h                    ;Peka p† Offset 03d0
        mov al,0cfh                     ;Skriv kod f”r IRET

        mov es:[bx],al                  ;Verkst„ll

        pop es
        ret

Skriv_IRET ENDP
;----------------------------------------------------------------------
;==== Ladda om vektorn att peka till 0000:03d0

New_Vector PROC NEAR

        push ds

        mov ax,0000h
        mov ds,ax                       ;New Segment -> DS

        mov dx,03d0h                    ;Mew Offset -> DX

        mov al,1ch                      ;Int 1ch
        mov ah,25h                      ;Skriv ny
        int 21h

        pop ds
        ret

New_Vector ENDP
;=====================================================================
Begin:
        call Skriv_IRET
        call New_Vector
        ret
;----------------------------------------------------------------------
CSEG    ENDS
        END Start
;-----------------------------------------------------------------------
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