如何让一个DIV里面的东西一直循环下去？

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                                 <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>
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在此基础上再追加