function abre_janela(width, height, nome, scrollbars) 
  {
   var top; var left;
   top = ( (screen.height/2) - (height/2) )
   left = ( (screen.width/2) - (width/2) )
   window.open('',nome,'width='+width+',height='+height+',scrollbars='+scrollbars+',toolbar=no,location=no,status=no,menubar=no,resizable=no,left='+left+',top='+top);
  }

  function semtab() { checatab=false; }
  function comtab() { checatab=true; }
  checatab=true;
  
  function muda(field1,field2,tamanho) {
    var elem1 = document.getElementById(field1);
    var elem2 = document.getElementById(field2);

    if ((elem1.value.length == tamanho) && (checatab) ) {
       elem2.focus();
       checatab=false;
    }
  }