var direction = 0;
var timer1;

function start_timer()
{
  if(direction!=0) timer1 = setInterval ('move()', 100);   
}

function stop_timer()
{
  clearInterval(timer1);
  direction = 0; 
}

function move()
{
 var obj = document.getElementById('my_scroll')
 if(direction==1)
 {
 	obj.scrollTop += 3;
 }
 else if(direction==-1)
 {
 	obj.scrollTop  -= 3;
}	

}