Abstract: A high-definition multimedia interface (HDMI) extender compatible with high-bandwidth digital content protection (HDCP) has a data receiver for receiving video/audio data and a data transmitter for transmitting the video/audio data to a display device. An Ethernet cable consisting of eight cores is connected between the data receiver and the data transmitter. When either the video/audio data or the display device complies with the HDCP, a voltage signal with level variation is transmitted between the data receiver and the data transmitter through the Ethernet cable to permit the display device to display the video/audio data.