var scrollSpeed =1;   // number of pixels to change every frame
  var scrollDepth =100; // height of your display box
  var scrollHeight=0;   // this will hold the height of your content
  var scrollDelay=50;  // delay between movements.

  var scrollPos=scrollDepth; // current scroll position
  var scrollMov=scrollSpeed; // for stop&start of scroll

  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; 
  }
  
  function scrMove() { scrollMov=scrollSpeed; }
  function scrStop() { scrollMov=0; }