The signaling method between the UPS and software. When the basicSignal used, the UPS changes the voltage level of some specific pins to notify the software of what critical event occurs. Usually, the UPS will inform software when a power failure or a low battery condition occurs. On the other hand, the software can change the voltage signal of a specific pin to ask the UPS to shut down (turn off). When the smartSignal used, the UPS asks like a standard communication device (such as mouse or modem). That means the UPS and software communicate with each other using a pre-defined protocol. The protocol should include at least the following commands: - query the power status of the UPS - query the power data of the UPS - command the UPS to shut down