Code    Segment
    assume CS:Code, DS:Data, SS:Stack

Start:
    mov ax, Code
    mov DS, AX

    ; Starting coordinate set
    mov dl,100
    mov dh,100
    push dx

    mov ax, 13h
    int 10h

    mov ax, 0a000h
    mov es, ax

    mov cl,128

Draw:
    pop dx
    xor ah,ah
    mov al,dh
    push dx
    mov bx,320
    mul bx
    pop dx
    add al,dl
    jnc Pixel
    inc ah

Pixel:
    push dx ; exact pixel coordinate
    mov di,ax
    inc cl
    mov es:[di],cl

Waitfor:
    xor ah,ah
    int 16h

    cmp al,27
    jz  Program_Vege

    ; Was the pressed key a movement one?
    cmp ah,75
    jz  Lefter
    cmp ah,77
    jz  Righter
    cmp ah,72
    jz  Upper
    cmp ah,80
    jz  Downer

    jmp Waitfor

; we change the dl (x) of dh (y) corordinate according to the pressed key (inc and dec 1 and -1)
Lefter:
    pop dx
    dec dl
    cmp dl,1
    jnc Keeper
    inc dl
Righter:
    pop dx
    inc dl
    cmp dl,250
    jc  Keeper
    dec dl
Upper:
    pop dx
    dec dh
    cmp dh,1
    jnc Keeper
    inc dh
Downer:
    pop dx
    inc dh
    cmp dh,200
    jc  Keeper
    dec dh
Keeper: ; and we save the new coordinate, yay!
    push dx
    jmp Draw

Program_Vege:
    mov ax,03h
    int 10h
    pop dx
    mov ax, 4c00h
    int 21h

Code    Ends

Data    Segment

Data    Ends

Stack   Segment

Stack   Ends
    End Start