1.6 - פסיקות - פתרון

תרגיל 1 – ‎print_A.asm

IDEAL
MODEL small
STACK 100h

CODESEG
start:
    mov ah, 02h      ; DOS - single character
    mov dl, 'A'
    int 21h

    mov ax, 4C00h    ; standard exit
    int 21h
END start

---

תרגיל 2 – ‎echo_char.asm

IDEAL
MODEL small
STACK 100h

CODESEG
start:
    mov ah, 01h      ; DOS: character input
    int 21h          ; AL ← the character

    mov ah, 0Eh      ; BIOS TTY output
    mov bh, 0
    mov bl, 7
    int 10h          ; displays AL

    mov ax, 4C00h
    int 21h
END start

---

תרגיל 3 – ‎print_string.asm

IDEAL
MODEL small
STACK 100h

DATASEG
msg db 'Hello, DOS!$',0

CODESEG
start:
    mov ax, @data
    mov ds, ax

    mov dx, offset msg
    mov ah, 09h
    int 21h           ; print

    mov ax, 4C00h
    int 21h
END start

---

תרגיל 4 – ‎read_and_print.asm

IDEAL
MODEL small
STACK 100h

DATASEG
buffer db 19          ; max length (up to 19)
       db 0           ; DOS will write the actual length here
       db 19 dup (0)  ; space for the letters
dollar db '$',0       ; used as terminator

CODESEG
start:
    mov ax, @data
    mov ds, ax

    ; --- read ---
    mov dx, offset buffer
    mov ah, 0Ah
    int 21h

    ; --- add '$' at the end ---
    mov bl, [buffer+1]   ; length that was typed
    mov bh, 0
    mov si, offset buffer
    add si, 2
    add si, bx           ; SI points after the characters
    mov byte ptr [si], '$'

    ; --- print ---
    mov dx, offset buffer+2
    mov ah, 09h
    int 21h

    mov ax, 4C00h
    int 21h
END start

---

תרגיל 5 – ‎custom_int60.asm

IDEAL
MODEL small
STACK 100h

DATASEG
old_off dw ?
old_seg dw ?

CODESEG
start:
    cli                     ; safety
    ; --- saving the old Vector ---
    mov ax, 0
    mov es, ax              ; ES=0000h -> IVT
    mov bx, 60h
    shl bx, 2               ; BX = 60h*4 = 0180h
    mov ax, word ptr es:[bx]
    mov old_off, ax
    mov ax, word ptr es:[bx+2]
    mov old_seg, ax

    ; --- installing a new Handler ---
    mov ax, seg myHandler
    mov word ptr es:[bx+2], ax
    mov ax, offset myHandler
    mov word ptr es:[bx], ax
    sti

    ; --- calling INT 60h twice ---
    int 60h
    int 60h

    ; --- restoring the old Vector ---
    cli
    mov ax, old_seg
    mov word ptr es:[bx+2], ax
    mov ax, old_off
    mov word ptr es:[bx], ax
    sti

    ; exit
    mov ax, 4C00h
    int 21h

; ----- Handler: prints '*' -----
myHandler:
    push ax
    mov  ah, 0Eh
    mov  al, '*'
    mov  bh, 0
    mov  bl, 7
    int  10h
    pop  ax
    iret
END start