The 1756-ESMNRM module shields the controller by blocking USB connections and SD card use indefinitely. It adds an additional layer of safety towards your application. Just one USB interface is usually furnished which may function the fallback conversation protocol. This USB interface is often utilized for Main configurations and troubleshooting. http://compactlogix02344.theideasblog.com/14530915/the-basic-principles-of-modicon-m340