stop=false
function roll(){
	if (!stop)
		window.scrollBy (0,1)
	if (document.body.scrollTop>=document.body.scrollHeight-document.body.clientHeight)
		window.setTimeout ('totop()',4000)		
	else
		window.setTimeout ('roll()',200)
}
function totop(){
	if (!stop)
		window.scrollTo (0,0)
	window.setTimeout ('roll()',200)
}
window.setTimeout ('roll()',2000) //Tempo em milisegundos para iniciar a rolagem