Модуль работы с видео-адаптером.

Unit Scroll;

interface

Procedure mScrollUp;               { Сдвиг экрана вверх на 1 пиксел }
Procedure mScrollDown;             { Сдвиг экрана вниз на 1 пиксел }
Procedure mScrollReset;
Procedure mWaitRetRace;            { Ожидание обратного хода луча } 

implementation

var ScrollPosition1,ScrollPosition2             :Word;

Procedure mScrollReset;Assembler;
Asm
        xor        ax,ax
        xor        bx,bx
        mov        [ScrollPosition1],ax
        mov        [ScrollPosition2],ax

        push       ax
        mov        dx, 3d4h
        mov        al, 0ch
        mov        ah, bh
        out        dx, ax

        mov        al, 0dh
        mov        ah, bl
        out        dx, ax

        pop        ax
        xchg       ah, al
        mov        al, 8
        out        dx, ax
        xchg       ah, al

End;

Procedure mScrollUp;Assembler;
Asm
        mov        ax,[ScrollPosition1]
        mov        bx,[ScrollPosition2]

        cmp        al, 15
        jnz        @NoLimit
        xor        ax, ax
        add        bx, 80
@NoLimit:
        inc        ax

        push       ax
        mov        dx, 3d4h
        mov        al, 0ch
        mov        ah, bh
        out        dx, ax

        mov        al, 0dh
        mov        ah, bl
        out        dx, ax

        pop        ax
        xchg       ah, al
        mov        al, 8
        out        dx, ax
        xchg       ah, al

        mov        [ScrollPosition1],ax
        mov        [ScrollPosition2],bx
End;

Procedure mScrollDown;Assembler;
Asm
        mov        ax,[ScrollPosition1]
        mov        bx,[ScrollPosition2]

        or         al, al
        jnz        @NoLimit2
        mov        al, 15
        sub        bx, 80
@NoLimit2:
        dec        ax

        push       ax
        mov        dx, 3d4h
        mov        al, 0ch
        mov        ah, bh
        out        dx, ax

        mov        al, 0dh
        mov        ah, bl
        out        dx, ax

        pop        ax
        xchg       ah, al
        mov        al, 8
        out        dx, ax
        xchg       ah, al

        mov        [ScrollPosition1],ax
        mov        [ScrollPosition2],bx
End;

Procedure mWaitRetRace;Assembler;
Asm
        mov        dx,03DAh
@Cikl1: in         al,dx
        test       al,08h
        jne        @Cikl1
@Cikl2: in         al,dx
        test       al,08h
        je         @Cikl2
End;

End.

Главный модуль.

Program Demo;

uses Scroll,Crt;

var A      :Word;

Begin
 mScrollReset;
 For A:=0 to 160 do
  Begin
   Delay(25);
   mScrollUp;
  End;
 For A:=0 to 160 do
  Begin
   Delay(25);
   mScrollDown;
  End;
 mScrollReset;
End.