code: private static void extractGroupASDU(byte[] apdu, DPTXlator t)
  	{
  		if (apdu.length < 2)
  			throw new KNXIllegalArgumentException("minimum APDU length is 2 bytes");
  		t.setData(apdu, apdu.length == 2 ? 1 : 2);
  	}
docs: Extracts the service data unit of an application layer protocol data unit into a
  DPT translator.
  <p>
  The whole service data unit is taken as data for translation. If the length of the
  supplied <code>apdu</code> is 2, a compact group APDU format layout is assumed.<br>
  On return of this method, the supplied translator contains the DPT items from the
  ASDU.
  
  @param apdu application layer protocol data unit, 2 &lt;= apdu.length
  @param t the DPT translator to fill with the ASDU