Help with countdown timer to goto and stop

Hi I need help adding a go to and stop at frame function  to the end of this countdown script

I've tried making a script of code but keep failing. Please help

countDown1F(00,50,50000,tf1);

function countDown2F(nStart:int,nEnd:int,duration:uint,tf:TextField) {

  if (nStart>=nEnd) {

  return null;

  } else {

  var t:Timer = new Timer(duration/(nEnd-nStart),nEnd-nStart);

t.addEventListener(TimerEvent.TIMER,function(e:TimerEvent){f2(e,nEnd,tf)});

  t.dispatchEvent(new TimerEvent(TimerEvent.TIMER));

  t.start();

  }

}

function f2(e:TimerEvent,nEnd:int,tf:TextField){

}

function countDown1F(nStart:int,nEnd:int,duration:uint,tf:TextField) {

  if (nStart>=nEnd) {

  return null;

  } else {

  var t:Timer = new Timer(duration/(nEnd-nStart),nEnd-nStart);

t.addEventListener(TimerEvent.TIMER,function(e:TimerEvent){f1(e,nEnd,tf)});

  t.dispatchEvent(new TimerEvent(TimerEvent.TIMER));

  t.start();

  }

}

function f1(e:TimerEvent,nEnd:int,tf:TextField){

  tf.text = formatF( (nEnd-e.target.currentCount));

}

function formatF(n:int):String {

var min:int = Math.floor(n/60);

var sec:int = n-min*60;

var a:Array = [min.toString(),sec.toString()];

for (var i:uint=0; i<a.length; i++) {

  while (a.length<2) {

  a="0"+a;

  }

}

return a[0] + ":" + a[1];

}