===================================
                                 <script>
                                     var stop=false;
                                     function ro()
                                     {
                                        if(stop)
                                        {
                                          return;
                                        }
                                        document.getElementById("Div1").scrollTop++;                           
                                        if(document.getElementById("Div1").scrollTop>120)
                                      {
                                          document.getElementById("Div1").scrollTop=0;
                                       }
                                      }
                                     window.setInterval(ro,100);     
                                </script>
====================================
在此基础上再追加