//....................
static TextView console;

// A callback for received data must be defined
private UsbSerialInterface.UsbReadCallback mCallback = new UsbSerialInterface.UsbReadCallback() {
    @Override
    public void onReceivedData(byte[] dat) {
        String data = new String(dat);

        console.append("RECEIVED DATA: "+data+"n"); //HERE IT CRASHING

        if (data.startsWith("call ")) {
            Intent callIntent = new Intent(Intent.ACTION_CALL);
            callIntent.setData(Uri.parse("tel:"+data.split(" ")[1]));
            try {
                startActivity(callIntent);
                console.append("Calling "+data.split(" ")[1]+" ...n");
            } catch (Exception e) { console.append("ERROR: Cant call "+data.split(" ")[1]+" ...n");}
        }
    }
};

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    final Button btn = (Button) findViewById(R.id.btn);
    final TextView console = (TextView) findViewById(R.id.console);
//...............