// lauch  a view data worker
 public static void lauchViewWorker(PLC plc)
 {
     // stop present worker if exist
     stopViewWorker();
     // start a new worker
     viewWorker = new modbusWorker(plc);
 }
 public static void stopViewWorker()
 {
     if (viewWorker != null)
     {
         viewWorker.stop();
         viewWorker = null;
     }
 }