code: public static synchronized ModbusSlave createUDPSlave(InetAddress address, int port) throws ModbusException {
          String key = ModbusSlaveType.UDP.getKey(port);
          if (slaves.containsKey(key)) {
              return slaves.get(key);
          }
          else {
              ModbusSlave slave = new ModbusSlave(address, port, false);
              slaves.put(key, slave);
              return slave;
          }
      }
docs: Creates a UDP modbus slave or returns the one already allocated to this port
  
  @param address IP address to listen on
  @param port    Port to listen on
  @return new or existing UDP modbus slave associated with the port
  
  @throws ModbusException If a problem occurs e.g. port already in use