{> Cut here. FileName= COL.PAS }

var   i,k:byte;
Const j :byte     = 0;
      dj:ShortInt = 1;

procedure vertical_retrace; assembler;
asm
  mov dx,$3da;@1:in al,dx;test al,8;jz @1;
  @2:in al,dx;test al,8;jnz @2
end;

procedure wait_line;assembler;
asm
  mov dx,$3da;@1:in al,dx;test al,1;jnz @1;
  @2:in al,dx;test al,1;jz @2
end;

procedure set_color(c,r,g,b:byte);assembler;
Asm
  mov dx,3C8h;mov al,c;out dx,al;inc dx;mov al,r;
  out dx,al;mov al,g;out dx,al;mov al,b;out dx,al
end;

begin
  Repeat
   Vertical_Retrace;
   asm cli end;
   for k:=0 to j do wait_line;
   For i:=0 to 7 do
    begin
     wait_line;
     set_color(0,0,0,i*8);
    end;
   For i:=7 downto 0 do
    begin
     wait_line;
     set_color(0,0,0,i*8);
    end;
   asm sti end;
   inc(j,dj);
   if (j>220)or(j<1) then dj:=-dj;
  Until Port[$60]=1;
end.