A method of reading data related to characteristics of a video receiver by a video transmitter, the video transmitter and the receiver being connected to each other through a digital interface, the video transmitter being arranged to transmit a digital video signal with content protection, the method comprising the steps of: changing the signal level of a hot plug detect terminal of the video receiver from a low level to a high level by the video receiver when the video receiver receives power; the video transmitter starting to read data related to the characteristics of the video receiver from the video receiver, when the video transmitter detects the change in the signal level of the hot plug detect terminal of the video receiver from the low level to the high level; transmitting the digital video signal to the video receiver by the video transmitter, the digital video signal being obtained by performing a content protection process, and the format being set for the digital video signal, on the basis of the data related to the characteristics of the video receiver read by the video transmitter; if the video receiver rewrites the data related to the characteristics of the video receiver while the signal level of the hot plug detect terminal is at the high level, the video receiver transmitting a first message and subsequently a second message to the video transmitter through a bidirectional communication interface included in the digital interface, whereby reading data related to the characteristics of the video receiver by the video transmitter is prohibited in the time period between the first message and the second message; and the video transmitter performing the content protection process, and transmitting the digital video signal, on the basis of the rewritten data related to the characteristics of the video receiver after receiving the second message from the video receiver. changing the signal level of a hot plug detect terminal of the video receiver from a low level to a high level by the video receiver when the video receiver receives power; the video transmitter starting to read data related to the characteristics of the video receiver from the video receiver, when the video transmitter detects the change in the signal level of the hot plug detect terminal of the video receiver from the low level to the high level; transmitting the digital video signal to the video receiver by the video transmitter, the digital video signal being obtained by performing a content protection process, and the format being set for the digital video signal, on the basis of the data related to the characteristics of the video receiver read by the video transmitter; if the video receiver rewrites the data related to the characteristics of the video receiver while the signal level of the hot plug detect terminal is at the high level, the video receiver transmitting a first message and subsequently a second message to the video transmitter through a bidirectional communication interface included in the digital interface, whereby reading data related to the characteristics of the video receiver by the video transmitter is prohibited in the time period between the first message and the second message; and the video transmitter performing the content protection process, and transmitting the digital video signal, on the basis of the rewritten data related to the characteristics of the video receiver after receiving the second message from the video receiver.