function MM_formt(e,src,mask) {
    if(window.event) { _TXT = e.keyCode; } 
    else if(e.which) { _TXT = e.which; }
    if(_TXT > 47 && _TXT < 58) { 
  var i = src.value.length; var saida = mask.substring(0,1); var texto = mask.substring(i)
  if (texto.substring(0,1) != saida) { src.value += texto.substring(0,1); } 
     return true; } else { if (_TXT != 8) { return false; } 
  else { return true; }
    }
}