A drive system for driving large capacity motors includes a motor and a variable frequency drive which accepts input from a three-phase power source. The conversion circuit is able to troubleshoot the communication signals between the indoor unit and outdoor unit of an air-conditioner. Each C3 code contains a plurality of P codes and Q codes. A second confidence value is determined for the second recognition result. A first inverter stage is coupled to a common gate of the first transistor stack. The security arrangements prevent an unauthorized or suspicious USB device from communicating with the host system, detect suspicious activity originating from a device which is already communicating with the host system and may provide notification to a user.