var scrollSpeed = 0.3;   // number of pixels to change every frame
var scrollDepth = 87; // height of your display box
var scrollHeight = 0;   // this will hold the height of your content
var scrollDelay = 25;  // delay between movements.

var scrollPos=scrollDepth; 
var scrollMov=scrollSpeed; 

function doScroll() {
	if(scrollHeight==0) { 
		getHeight(); 
	}
   	scrollPos-=scrollMov;
   	
	if(scrollPos<(0-scrollHeight)) { 
		scrollPos=scrollDepth; 
	}
   	document.getElementById('scrollTxt').style.top=scrollPos+'px';
   	setTimeout('doScroll();', scrollDelay);
}
  
function getHeight() {
	scrollHeight=document.getElementById('scrollTxt').offsetHeight; 
}
  
window.onload = doScroll;