Patent Publication Number: US-9900653-B2

Title: Transmission device and reception device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation of U.S. application Ser. No. 14/806,150 (U.S. Pat. No. 9,525,908) filed Jul. 22, 2015, which is a continuation of U.S. application Ser. No. 14/492,598 (U.S. Pat. No. 9,154,831) filed Sep. 22, 2014, which is a continuation of U.S. patent application Ser. No. 12/451,269 (U.S. Pat. No. 8,898,727) filed Jan. 14, 2010, which is a national phase entry under 35 U.S.C. § 371 of International Application No. PCT/JP2009/054193 filed Mar. 5, 2009, published on Sep. 11, 2009 as WO 2009/110561 A1, which claims priority from Japanese Patent Application No. JP 2008-055576 filed in the Japanese Patent Office on Mar. 5, 2008, Japanese Patent Application No. JP2008-136063 filed in the Japanese Patent Office on May 23, 2008 and Japanese Patent Application No. JP 2008-208302 filed in the Japanese Patent Office on Aug. 13, 2008; the disclosures of which are hereby incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present invention relates to a transmission device and a reception device. Specifically, the present invention relates to, in the case of including a communication unit configured to execute communication via a communication path made up of a pair of differential transmission paths included in a transmission path, a transmission device or the like configured to enable an external device to transmit a signal suitably by allowing the external device to recognize information relating to the communication unit thereof. 
     BACKGROUND ART 
     In recent years, for example, HDMI (High Definition Multimedia Interface) has come into widespread use as a communication interface for transmitting digital video signals, i.e., uncompressed (baseband) video signals (hereafter, referred to as “image data” as appropriate) and digital audio signals (hereafter, referred to as “audio data” as appropriate) along with the video signal thereof from a DVD (Digital Versatile Disc) recorder, a set top box, or another AV source (Audio Visual source) to a television receiver, a projector, or another display, at high speed. For example, description has been made in Patent Document 1 regarding the details of the HDMI standard. 
     Patent Document 1: WO 2002/078336 
     DISCLOSURE OF INVENTION 
     Technical Problem 
     With the current HDMI standard, a transmission device (source device) can determine whether or not a reception device (sink device) is an eHDMI-compatible device, according to the voltage state of the reserve line of the HDMI cable. Here, the transmission device or reception device is compatible with eHDMI means that this transmission device or reception device includes a communication unit configured to execute communication using a communication path made up of predetermined lines of the HDMI cable (e.g., a reserve line and an HPD line). 
     However, the reception device has difficulty in recognizing whether or not the transmission device is an eHDMI-compatible device. In the case that the transmission device is in a busy state, the reception device has difficulty in recognizing this busy state. Therefore, reception devices have sometimes transmitted an unnecessary signal to a transmission device incompatible with eHDMI, or a transmission device compatible with eHDMI in a busy state. 
     An object of the present invention is to allow a reception device to transmit a signal to a transmission device suitably. 
     Technical Solution 
     One concept of the present invention is a transmission device comprising: 
     a video signal transmission unit configured to transmit video signals to an external device via a transmission path with a plurality of channels using a differential signal; 
     a communication unit configured to communicate with the external device via a communication path made up of a pair of differential transmission paths included in the transmission path; 
     a function information transmission unit configured to transmit first function information indicating that the transmission device includes the communication unit to the external device via a control data line making up the transmission path; and 
     a function information reception unit configured to receive second function information indicating that the external device includes a communication unit configured to execute communication via the communication path, which is transmitted from the external device. 
     Also, another concept of the present invention is a reception device comprising: 
     a video signal reception unit configured to receive video signals from an external device via a transmission path with a plurality of channels using a differential signal; 
     a communication unit configured to communicate with the external device via a communication path made up of a pair of differential transmission paths included in the transmission path; 
     a function information transmission unit configured to transmit first function information indicating that the reception device includes the communication unit to the external device via a control data line making up the transmission path; and 
     a function information reception unit configured to receive second function information indicating that the external device includes a communication unit configured to execute communication via the communication path, which is transmitted from the external device. 
     With the present invention, the transmission device includes a video signal transmission unit configured to transmit video signals to an external device (reception device) via a transmission path with a plurality of channels using a differential signal, and is, for example, an HDMI source device. The transmission device is provided with a communication unit configured to communicate with the external device via a communication path made up of a pair of differential transmission paths included in the transmission path. For example, at least one of the pair of differential transmission paths of the communication path includes a function for notifying the connection state of the external device using a DC bias potential. For example, the pair of differential transmission paths included in the transmission path is a reserve line and an HPD line making up an HDMI cable. 
     The function information indicating that the transmission device includes the communication unit is transmitted to the external device via the control data line. For example, the control data line is the CEC line of the HDMI cable, and the function information is transmitted to the external device as a CEC signal. This function information may include information of a transmission format (application) that it (transmission device) can support itself. 
     The reception device includes a video signal reception unit configured to receive video signals from an external device (transmission device) via a transmission path with a plurality of channels using a differential signal, and is, for example, an HDMI sink device. The reception device is provided with a communication unit configured to communicate with the external device via a communication path made up of a pair of differential transmission paths included in the transmission path. For example, at least one of the pair of differential transmission paths of the communication path includes a function for notifying the connection state of the external device using a DC bias potential. For example, the pair of differential transmission paths included in the transmission path is a reserve line and an HPD line making up an HDMI cable. 
     With the reception device, the function information transmitted from the external device is received via the control data line. For example, the control data line is the CEC line of the HDMI cable, and the function information is received from the external device as a CEC signal. 
     The function information indicating that the reception device includes the communication unit is transmitted to the external device via the control data line. This function information may include the information of a transmission format (application) that it (reception device) can support itself. With the transmission device, the function information transmitted from the external device is received via the control data line. 
     Thus, in the case that the transmission device includes the communication unit, the function information indicating that the transmission device includes the communication unit is transmitted to the reception device from the transmission device, and this function information is received at the reception device. Therefore, the reception device can recognize whether or not the external device (transmission device) includes the communication unit, and accordingly, transmitting an unnecessary signal to the external device having no communication unit via the communication path can be avoided. Also, in the case that the function information includes transmission format information that the external device can support, the reception device can readily know the transmission format that the external device can support from the information thereof. 
     Also, in the case that the reception device includes the communication unit, the function information indicating that the reception device includes the communication unit is transmitted to the transmission device from the reception device, and this function information is received at the transmission device. Therefore, the transmission device can recognize whether or not the external device (reception device) includes the communication unit, and accordingly, transmit an unnecessary signal to the external device having no communication unit via the communication path can be avoided. Also, in the case that the function information includes transmission format information that the external device can support, the transmission device can readily know the transmission format that the external device can support from the information thereof. 
     With the present invention, for example, an arrangement may be made wherein the reception device includes a transmission request transmission unit configured to transmit a transmission request for the function information to the external device (transmission device), the transmission device includes a transmission request reception unit configured to receive a transmission request for the function information transmitted from the external device (reception device), and the function information transmission unit of the transmission device transmits the function information to the external device (reception device) when the transmission request reception unit receives the transmission request. In this case, the reception device can confirm whether or not the external device includes the communication unit, at arbitrary timing (e.g., at the time of power-on, at the time of input change, or the like) by transmitting a transmission request for the function information to the external device. 
     Advantageous Effects 
     The present invention allows, in the case of including a communication unit configured to execute communication via a communication path made up of a pair of differential transmission paths included in a transmission path, the external device to recognize information relating to the communication unit thereof, and the external device can transmit a signal suitably, such as avoiding transmission of unnecessary packets, or the like. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram illustrating a configuration example of an AV system serving as an embodiment of the present invention. 
         FIG. 2  is a block diagram illustrating a configuration example of a disk recorder (source device) making up the AV system. 
         FIG. 3  is a block diagram illustrating a configuration example of a television receiver (sink device) making up the AV system. 
         FIG. 4  is a block diagram illustrating a configuration example of an HDMI transmission unit (HDMI source) and an HDMI reception unit (HDMI sink). 
         FIG. 5  is a block diagram illustrating a configuration example of an HDMI transmitter and an HDMI receiver. 
         FIG. 6  is a diagram illustrating the structure of TMDS transmission data. 
         FIG. 7  is a diagram illustrating the pin array (type A) of an HDMI terminal. 
         FIG. 8  is a connection diagram illustrating a configuration example of a high-speed data line interface of the disk recorder and the television receiver. 
         FIG. 9  is a connection diagram illustrating a configuration example of the high-speed data line interface and the like of the disk recorder and the television receiver. 
         FIG. 10  is a diagram illustrating the data structure of AVI InfoFrame. 
         FIG. 11  is a diagram illustrating the structure of CEC data to be transmitted with a CEC line. 
         FIG. 12  is a diagram illustrating a structure example of a header block. 
         FIG. 13  is a diagram illustrating logical addresses to be set according to the type of each device with HDMI. 
         FIG. 14  is a sequence diagram for describing an example of use of an &lt;Exchange Supported Channels Info&gt; message. 
         FIG. 15  is a diagram illustrating a device configuration example of the AV system. 
         FIG. 16  is a sequence diagram for describing an example of use of an &lt;Active Supported Channels&gt; message. 
         FIG. 17  is a sequence diagram for describing an example of use of an &lt;Active Supported Channels&gt; message. 
         FIG. 18  is a block diagram illustrating a configuration example of the AV system. 
         FIG. 19  is a diagram for describing an example wherein an HPD signal is set to “H” by changing the voltage of a power supply line without using a &lt;Request HPD=H&gt; message. 
         FIG. 20  is a connection diagram illustrating a configuration example of the high-speed data line interface and the like of the disk recorder and the television receiver. 
         FIG. 21  is a diagram illustrating a voltage change example of the HPD line and a reserve line. 
         FIG. 22  is a block diagram illustrating a configuration example of the disk recorder and the television receiver, in the case that function information and compatible transmission format information is transmitted from the disk recorder to the television receiver, and also compatible transmission format information is transmitted from the television receiver to the disk recorder. 
         FIG. 23  is a diagram illustrating a voltage control example of the HPD line with the television receiver (sink device) side, and a voltage control example of the reserve line with the disk recorder (source device) side and the television receiver (sink device) side corresponding thereto. 
         FIG. 24  is a block diagram illustrating a configuration example of a television receiver including multiple, e.g., three HDMI terminals. 
         FIG. 25  is a diagram illustrating an operation example in the case that the sink device is multi-HDMI input. 
         FIG. 26  is a flowchart illustrating an example of a processing procedure at the time of the CPU of the television receiver (sink device) executing a detection operation as to predetermined HDMI input. 
         FIG. 27  is a diagram illustrating a voltage change example of the HPD line and the reserve line, in the case that the CPU device of the sink device determines that the source device on the partner side is an eHDMI-incompatible device. 
         FIG. 28  is a diagram for describing retry processing wherein at the time of reply from the source device having not arrived even if 100 milliseconds elapse, transmission of the function information and the like is requested as to the source device on the partner side again. 
         FIG. 29  is a flowchart illustrating an example of the processing procedure of the CPU of the disk recorder (source device). 
         FIG. 30  is a block diagram illustrating a configuration example of the disk recorder and the television receiver, in the case that function information and compatible transmission format information is transmitted from the disk recorder to the television receiver, and also compatible transmission format information is transmitted from the television receiver to the disk recorder. 
         FIG. 31  is a diagram illustrating a voltage control example of the reserve line. 
         FIG. 32  is a diagram illustrating an operation example in the case that the sink device is multi-HDMI input. 
         FIG. 33  is a flowchart illustrating, in the case of outputting a request from the sink device, an example of the processing procedure of this sink device. 
         FIG. 34  is a diagram illustrating a voltage change example of the reserve line, in the case that the CPU of the sink device determines that the source device on the partner side is an eHDMI-incompatible device. 
         FIG. 35  is a diagram for describing retry processing wherein at the time of reply from the source device having not arrived even if two seconds elapse, transmission of the function information and the like is requested as to the source device on the partner side again. 
         FIG. 36  is a flowchart illustrating an example of the processing procedure of the sink device in the case of outputting a request from the source device. 
         FIG. 37  is a flowchart illustrating an example of the processing procedure of the sink device in the case of outputting a request from the source device. 
         FIG. 38  is a flowchart illustrating an example of the processing procedure of the sink device in the case of outputting a request from the source device. 
         FIG. 39  is a block diagram illustrating another configuration example of the AV system. 
     
    
    
     EXPLANATION OF REFERENCE NUMERALS 
       10  AV system,  11 ,  12  CDC device,  13  Non-CDC device,  11   a ,  11   b ,  12   a ,  13   a  HDMI terminal,  14 ,  15  HDMI cable,  200  AV system,  210  disk recorder,  211  HDMI terminal,  212  HDMI transmission unit,  213  high-speed data line interface,  250  television receiver,  251  HDMI terminal,  252  HDMI reception unit,  253  high-speed data line interface,  350  HDMI cable,  417  SPDIF reception circuit,  449  SPDIF transmission circuit 
     BEST MODE FOR CARRYING OUT THE INVENTION 
     Hereinafter, an embodiment of the present invention will be described with reference to the drawings.  FIG. 1  illustrates a configuration example of an AV (Audio Visual) system  200  serving an embodiment. This AV system  200  includes a disk recorder  210  serving as a source device, and a television receiver  250  serving as a sink device. With this AV system  200 , the disk recorder  210  and the television receiver  250  are eHDMI-compatible devices. Here, to be an eHDMI-compatible device means to include a communication unit configured to execute communication using a communication path with a reserve line and an HPD line making up an HDMI cable. 
     The disk recorder  210  and the television receiver  250  are connected via an HDMI cable  350 . The disk recorder  210  is provided with an HDMI terminal  211  to which an HDMI transmission unit (HDMITX)  212  and a high-speed data line interface (I/F)  213  are connected. The television receiver  250  is provided with an HDMI terminal  251  to which an HDMI reception unit (HDMIRX)  252  and a high-speed data line interface (I/F)  253  are connected. One end of the HDMI cable  350  is connected to the HDMI terminal  211  of the disk recorder  210 , and the other end of this HDMI cable  350  is connected to the HDMI terminal  251  of the television receiver  250 . 
     With the AV system  200  shown in  FIG. 1 , the video signals played at the disk recorder  210  are supplied to the television receiver  250  via the HDMI cable  350 , and an image is displayed at this television receiver  250 . Also, the audio signal played at the disk recorder  210  is supplied to the television receiver  250  via the HDMI cable  350 , and audio is output from a speaker of this television receiver  250 . 
       FIG. 2  illustrates a configuration example of the disk recorder  210 . This disk recorder  210  includes an HDMI terminal  211 , an HDMI transmission unit  212 , a high-speed data line interface  213 , an antenna terminal  214 , a digital tuner  215 , a demultiplexer  216 , an internal bus  217 , a recording unit interface  218 , a DVD/BD drive  219 , an HDD (Hard Disk Drive)  220 , a CPU (Central Processing Unit)  221 , flash ROM (Read Only Memory)  222 , DRAM (Dynamic Random Access Memory)  223 , an Ethernet interface (Ethernet I/F)  224 , a network terminal  225 , a DTCP (Digital Transmission Content Protection) circuit  226 , an MPEG decoder  227 , a graphics generating circuit  228 , a video output terminal  229 , and an audio output terminal  230 . Note that “Ethernet” is a registered trademark. 
     The HDMI transmission unit (HDMI source)  212  transmits baseband video (image) and audio data from the HDMI terminal  211  by communication conforming to HDMI. The details of this HDMI transmission unit  212  will be described later. The high-speed data line interface  213  is a bidirectional communication interface using predetermined lines making up an HDMI cable (a reserve line and an HPD line in the present embodiment). The details of this high-speed data line interface  213  will be described later. 
     The antenna terminal  214  is a terminal which inputs a television broadcast signal received at a reception antenna (not shown). The digital tuner  215  processes the television broadcast signal to be input to the antenna terminal  214  to output a predetermined transport stream. The demultiplexer  216  extracts a partial TS (Transport Stream) (TS packet of video data, TS packet of audio data) corresponding to a predetermined selected channel from the transport stream obtained at the digital tuner  215 . 
     Also, the demultiplexer  216  extracts PSI/SI (Program Specific Information/Service Information) from the transport stream obtained at the digital tuner  215 , and outputs this to the CPU  221 . With the transport stream obtained at the digital tuner  215 , multiple channels are multiplexed. Processing for extracting the partial TS of an arbitrary channel from this transport stream can be executed by obtaining the information of the packet ID (PID) of this arbitrary channel from the PSI/SI (PAT/PMT). 
     The CPU  221 , flash ROM  222 , DRAM  223 , demultiplexer  216 , Ethernet interface  224 , and recording unit interface  218  are connected to the internal bus  217 . The DVD/BD drive  219  and HDD  220  are connected to the internal bus  217  via the recording unit interface  218 . The DVD/BD drive  219  and HDD  220  record the partial TS extracted at the demultiplexer  216 . Also, each of the DVD/BD drive  219  and HDD  220  plays the partial TS recorded in a recording medium. 
     The MPEG decoder  227  obtains video data by subjecting a video PES packet making up the partial TS extracted at the demultiplexer  216 , or played at the DVD/BD drive  219  or HDD  220  to decode processing. Also, the MPEG decoder  227  obtains audio data by subjecting an audio PES packet making up this partial TS to decode processing. 
     The graphics generating circuit  228  subjects the video data obtained at the MPEG decoder  227  to graphics data convolution processing or the like as appropriate. The video output terminal  229  outputs the video data output from the graphics generating circuit  228 . The audio output terminal  230  outputs the audio data obtained at the MPEG decoder  227 . 
     The DTCP circuit  226  encrypts the partial TS extracted at the demultiplexer  216 , or the partial TS played at the DVD/BD drive  219  or HDD  220  as appropriate. Also, the DTCP circuit  226  decrypts the encrypted data supplied from the network terminal  225  or high-speed data line interface  213  to the Ethernet interface  224 . 
     The CPU  221  controls the operation of each unit of the disk recorder  210 . The flash ROM  222  executes storing of control software, and storing of data. The DRAM  223  makes up a work area of the CPU  221 . The CPU  221  renders the software and data read out from the flash ROM  222  onto the DRAM  223 , activates the software to control each unit of the disk recorder  210 . 
     The operation of the disk recorder  210  shown in  FIG. 2  will be described briefly. 
     The television broadcast signal input to the antenna terminal  214  is supplied to the digital tuner  215 . With this digital tuner  215 , the television broadcast signal is subjected to processing to extract a predetermined transport stream, and this predetermined transport stream is supplied to the demultiplexer  216 . With the demultiplexer  216 , the partial TS (TS packet of video data, TS packet of audio data) corresponding to a predetermined channel is extracted from the transport stream. This partial TS is supplied to the DVD/BD drive  219  or HDD  220  via the recording unit interface  218 , and is recorded therein based on a recording instruction from the CPU  221 . 
     Also, as described above, the partial TS extracted at the demultiplexer  216 , or the partial TS played at the DVD/BD drive  219  or HDD  220  is supplied to the MPEG decoder  227 . With this MPEG decoder  227 , the video PES packet made up of a TS packet of video data is subjected to decode processing, and video data is obtained. This video data is subjected to graphics data convolution processing or the like at the graphics generating circuit  228 , and is then output to the video output terminal  229 . Also, with the MPEG decoder  227 , the audio PES packet made up of a TS packet of audio data is subjected to decode processing, and audio data is obtained. This audio data is output to the audio output terminal  230 . 
     The video (image) data and audio data obtained at the MPEG decoder  227  corresponding to the partial TS played at the DVD/BD drive  219  or HDD  220  is supplied to the HDMI transmission unit  212 , and is transmitted to an HDMI cable connected to the HDMI terminal  211 . 
     With the high-speed data line interface  213 , an IP packet including a remote control code transmitted via the predetermined lines of the HDMI cable connected to the HDMI terminal  211  is received. This IP packet is supplied to the CPU  221  via the Ethernet interface  224 . In the case that the remote control code included in this IP packet relates to the control of the disk recorder  210 , the CPU  221  controls each unit of the disk recorder  210  based on this remote control code. 
     Also, in the event that the partial TS extracted at the demultiplexer  216 , or the partial TS played at the DVD/BD drive  219  or HDD  220  is transmitted to a network, this partial TS is encrypted at the DTCP circuit  226 , and is then output to the network terminal  225  via the Ethernet interface  224 . 
       FIG. 3  illustrates a configuration example of the television receiver  250 . This television receiver  250  includes an HDMI terminal  251 , an HDMI reception unit  252 , a high-speed data line interface  253 , an antenna terminal  257 , a digital tuner  258 , a demultiplexer  259 , an MPEG (Moving Picture Expert Group) decoder  260 , a video/graphics processing unit  261 , a panel driving circuit  262 , a display panel  263 , an audio signal processing circuit  264 , an audio amplifying circuit  265 , a speaker  266 , a DTCP circuit  267 , an internal bus  270 , a CPU  271 , flash ROM  272 , DRAM  273 , an Ethernet interface (Ethernet I/F)  274 , a network terminal  275 , a remote control reception unit  276 , and a remote control transceiver  277 . 
     The antenna terminal  257  is a terminal for inputting the television signal received at a reception antenna (not shown). The digital tuner  258  subjects the television broadcast signal input to the antenna terminal  257  to processing, and outputs the predetermined transport stream corresponding to the channel selected by the user. The demultiplexer  259  extracts the partial TS (Transport Stream) (TS packet of video data, TS packet of audio data) corresponding to the channel selected by the user from the transport stream obtained at the digital tuner  258 . 
     Also, the demultiplexer  259  extracts PSI/SI (Program Specific Information/Service Information) from the transport stream obtained at the digital tuner  258 , and outputs this to the CPU  271 . With the transport stream obtained at the digital tuner  258 , multiple channels are multiplexed. The processing for extracting the partial TS of an arbitrary channel from this transport stream at the demultiplexer  259  can be executed by obtaining the information of the packet ID (PID) of this arbitrary channel from the PSI/SI (PAT/PMT). 
     The MPEG decoder  260  subjects the video PES (Packetized Elementary Stream) packet made up of the TS packets of the video data obtained at the demultiplexer  259  to decode processing, thereby obtaining video data. Also, the MPEG decoder  260  subjects the audio PES packet made up of the TS packets of the audio data obtained at the demultiplexer  259 , thereby obtaining audio data. Note that this MPEG decoder  260  subjects the video and audio PES packets obtained by being decrypted at the DTCP circuit  267  to decode processing as appropriate, thereby obtaining video data and audio data. 
     The video/graphics processing circuit  261  subjects the video data obtained at the MPEG decoder  260  to multi screen processing, graphics data convolution processing, or the like as appropriate. The panel driving circuit  262  drives the display panel  263  based on the video data output from the video/graphics processing circuit  261 . The display panel  263  is configured of, for example, an LCD (Liquid Crystal Display), PDP (Plasma Display Panel), or the like. The audio signal processing circuit  264  subjects the audio data obtained at the MPEG decoder  260  to necessary processing such as D/A conversion or the like. The audio amplifying circuit  265  amplifies the audio signal output from the audio signal processing circuit  264 , and supplies this to the speaker  266 . 
     The DTCP circuit  267  encrypts the partial TS extracted at the demultiplexer  259  as appropriate. Also, the DTCP circuit  267  decrypts the encrypted data supplied from the network terminal  275  or high-speed data line interface  253  and  256  to the Ethernet interface  274 . 
     The CPU  271  controls the operation of each unit of the television receiver  250 . The flash ROM  272  executes storing of control software, and storing of data. The DRAM  273  makes up a work area of the CPU  271 . The CPU  271  renders the software and data read out from the flash ROM  272  onto the DRAM  273 , activates the software to control each unit of the television receiver  250 . The remote control reception unit  276  receives the remote control signal (remote control code) transmitted from the remote control transceiver  277 , and supplies this to the CPU  271 . The CPU  271 , flash ROM  272 , DRAM  273 , and Ethernet interface  274  are connected to the internal bus  270 . 
     The HDMI reception unit (HDMI sink)  252  receives baseband video (image) and audio data supplied to the HDMI terminal  251  by communication conforming to HDMI. The details of this HDMI reception unit  252  will be described later. The high-speed data line interface  253  is a bidirectional communication interface using predetermined lines making up an HDMI cable (a reserve line and an HPD line in the present embodiment). The details of this high-speed data line interface  253  will be described later. 
     The operation of the television receiver  250  shown in  FIG. 3  will be described briefly. 
     The television broadcast signal input to the antenna terminal  157  is supplied to the digital tuner  258 . With this digital tuner  258 , the television broadcast signal is subjected to processing, the predetermined transport stream corresponding to the channel selected by the user is output, and this predetermined transport stream is supplied to the demultiplexer  259 . With this demultiplexer  259 , the partial TS (TS packet of video data, TS packet of audio data) corresponding to the channel selected by the user is extracted from the transport stream, and this partial TS is supplied to the MPEG decoder  260 . 
     With the MPEG decoder  260 , the video PES packet made up of a TS packet of video data is subjected to decode processing, thereby obtaining video data. This video data is subjected to multi screen processing, graphics data convolution processing, or the like at the video/graphics processing circuit  261  as appropriate, and is then supplied to the panel driving circuit  262 . Therefore, the image corresponding to the channel selected by the user is displayed on the display panel  263 . 
     Also, with the MPEG decoder  260 , the audio PES packet made up of a TS packet of audio data is subjected to decode processing, thereby obtaining audio data. This audio data is subjected to necessary processing such as D/A conversion or the like at the audio signal processing circuit  264 , and further, is amplified at the audio amplifying circuit  265 , and is then supplied to the speaker  266 . Therefore, the audio corresponding to the channel selected by the user is output from the speaker  266 . 
     In the event that the partial TS extracted at the demultiplexer  259  is transmitted to a network at the time of receiving the above television broadcast signal, this partial TS is encrypted at the DTCP circuit  267 , and is then output to the network terminal  275  via the Ethernet interface  274 . 
     With the remote control reception unit  276 , the remote control code (remote control signal) transmitted from the remote control transceiver  277  is received, and this remote control code is supplied to the CPU  271 . In the case that the remote control code relates to the control of the television receiver  250 , the CPU  271  controls each unit of the television receiver  250  based on this remote control code. 
     Also, with the CPU  271 , an IP packet including the remote control code supplied from the remote control reception unit  276  is generated. This IP packet is output to the HDMI terminal  251  via the Ethernet interface  274  and high-speed line interface  253 . 
     Also, this IP packet is transmitted to the network as appropriate. In this case, this IP packet is output to the network terminal  275  via the Ethernet interface  274 . Also, this IP packet is output to the HDMI terminal  251  via the Ethernet interface  274  and high-speed data line interface  253 . 
     Note that the encrypted partial TS supplied from the network terminal  275  to the Ethernet interface  274 , or supplied from the HDMI terminal  251  to the Ethernet interface  274  via the high-speed data line interface  253 , is decrypted at the DTCP circuit  267 , and is then supplied to the MPEG decoder  260 . Hereafter, the operation of the television receiver  250  is the same operation as at the time of receiving the above television broadcast signal, where an image is displayed on the display panel  263 , and audio is output from the speaker  266 . 
     Also, with the HDMI reception unit  252 , the video (image) data and audio data input to the HDMI terminal  251  via the HDMI cable is obtained. This video data and audio data is each supplied to the video/graphics processing circuit  261  and the audio signal processing circuit  264 . Hereafter, the operation of the television receiver  250  is the same operation as at the time of receiving the above television broadcast signal, where an image is displayed on the display panel  263 , and audio is output from the speaker  266 . 
       FIG. 4  illustrates a configuration example of the HDMI transmission unit (HDMI source)  212  of the disk recorder  210 , and the HDMI reception unit (HDMI sink)  252  of the television receiver  250  with the AV system  200  in  FIG. 1 . 
     The HDMI source  212  transmits the differential signals corresponding to the pixel data of uncompressed one screen worth of image to the HDMI sink  252  in one direction using multiple channels during a valid image section wherein a horizontal retrace line section and a vertical retrace line section are removed from a section from a vertical synchronizing signal to the next vertical synchronizing signal (hereafter, also referred to as “active video section” as appropriate), and also transmits the differential signals corresponding to at least audio data along with the image, control data, other auxiliary data, and the like along with the image to the HDMI sink  252  in one direction using multiple channels during a horizontal retrace line section and a vertical retrace line section. 
     That is to say, the HDMI source  212  includes a transmitter  81 . The transmitter  81  converts, for example, the pixel data of an uncompressed image to the corresponding differential signals, and serially transmits these to the HDMI sink  252  connected thereto via the HDMI cable  350  in one direction using three TMDS channels #0, #1, and #2, which are multiple channels. 
     Also, the transmitter  81  converts audio data along with an uncompressed image, and further, necessary control data, other auxiliary data, and the like into the corresponding differential signals, and serially transmits these to the HDMI sink  252  connected thereto via the HDMI cable  350  in one direction using the three TMDS channels #0, #1, and #2. 
     Further, the transmitter  81  transmits the pixel clock synchronized with the pixel data to be transmitted using the three TMDS channels #0, #1, and #2 to the HDMI sink  252  connected thereto via the HDMI cable  350  using a TMDS clock channel. Here, with one of the TMDS channel #i (i=0, 1, 2), the pixel data of 10 bits is transmitted during one clock of the pixel clock. 
     The HDMI sink  252  receives the differential signals corresponding to pixel data, transmitted from the HDMI source  212  in one direction using multiple channels during an active video section, and also receives the differential signals corresponding to audio data and control data, transmitted from the HDMI source  212  in one direction during a horizontal retrace line section and a vertical retrace line section. 
     That is to say, the HDMI sink  252  includes a receiver  82 . The receiver  82  receives the differential signals corresponding to pixel data, transmitted in one direction from the HDMI source  212  connected thereto via the HDMI cable  350  using the TMDS channels #0, #1, and #2, in sync with the pixel clock transmitted similarly from the HDM source  212  using the TMDS clock channel. 
     The transmission channels of the HDMI system made up of the HDMI source  212  and the HDMI sink  252  include, in addition to the three TMDS channels #0 through #2 serving as transmission channels for serially transmitting pixel data and audio data in one direction in sync with the pixel clock, and the TMDS clock channel serving as a transmission channel for transmitting the pixel clock, transmission channels referred to as a DDC (Display Data Channel)  83  and a CEC line  84 . 
     The DDC  83  is made up of two unshown signal lines included in the HDMI cable  350 , and is used for the HDMI source  212  reading out E-EDID (Enhanced Extended Display Identification Data) from the HDMI sink  252  connected thereto via the HDMI cable  350 . 
     That is to say, the HDMI sink  252  includes, in addition to the HDMI receiver  81 , EDID ROM (Read Only Memory)  85  which stores E-EDID that is performance information relating to the performance (configuration/capability) of itself. The HDMI source  212  reads out the E-EDID of this HDMI sink  252  from the HDMI sink  252  connected thereto via the HDMI cable  350 , via the DDC  83 , and recognizes the settings of the performance of the HDMI sink  252 , i.e., for example, the format (profile) of the image corresponding to the electronic equipment including the HDMI sink  252 , for example, RGB, YCbCr4:4:4, YCbCr4:2:2, or the like. 
     The CEC line  84  is made up of a single signal line not shown included in the HDMI cable  350 , and is used for executing the bidirectional communication of data for control between the HDMI source  212  and the HDMI sink  252 . 
     Also, the HDMI cable  350  includes a line (HPD line)  86  connected to a pin called HPD (Hot Plug Detect). A source device uses this line  86 , whereby connection of a sink device can be detected. Also, the HDMI cable  350  includes a line  87  used for supplying power from a source device to a sink device. Further, the HDMI cable  351  includes a reserve line  88 . 
       FIG. 5  illustrates a configuration example of the HDMI transmitter  81  and the HDMI receiver  82  in  FIG. 4 . 
     The transmitter  81  includes three encoders/serializers  81 A,  81 B, and  81 C corresponding to the three TMDS channels #0, #1, and #2, respectively. Each of the encoders/serializers  81 A,  81 B, and  81 C encodes image data, auxiliary data, and control data supplied thereto, converts this from parallel data to serial data, and transmits this using a differential signal. Here, in the case that the image data includes, for example, three components of R (Red), G (Green), and B (Blue), the B component is supplied to the encoder/serializer  81 A, the G component is supplied to the encoder/serializer  81 B, and R component is supplied to the encoder/serializer  81 C. 
     Also, examples of the auxiliary data include audio data and control packet, the control packet is supplied to, for example, the encoder/serializer  81 A, and the audio data is supplied to the encoders/serializers  81 B and  81 C. 
     Further, examples of the control data include a 1-bit vertical synchronizing signal (VSYNC), a 1-bit horizontal synchronizing signal (HSYNC), and 1-bit control bits CTL 0 , CTL 1 , CTL 2 , and CTL 3 . The vertical synchronizing signal and the horizontal synchronizing signal are supplied to the encoder/serializer  81 A. The control bits CTL 0  and CTL  1  are supplied to the encoder/serializer  81 B, and the control bits CTL 2  and CTL  3  are supplied to the encoder/serializer  81 C. 
     The encoder/serializer  81 A transmits the B component of image data, vertical synchronizing signal and horizontal synchronizing signal, and auxiliary data supplied thereto, in a time-sharing manner. That is to say, the encoder/serializer  81 A takes the B component of image data supplied thereto as parallel data in increments of 8 bits that are the number of fixed bits. Further, the encoder/serializer  81 A encodes the parallel data thereof to convert this into serial data, and transmits this using the TMDS channel #0. 
     Also, the encoder/serializer  81 A encodes the 2-bit parallel data of a vertical synchronizing signal and a horizontal signal supplied thereto to convert this into serial data, and transmits this using the TMDS channel #0. Further, the encoder/serializer  81 A takes the auxiliary data supplied thereto as parallel data in increments of 4 bits. Further, the encoder/serializer  81 A encodes the parallel data thereof to convert this into serial data, and transmits this using the TMDS channel #0. 
     The encoder/serializer  81 B transmits the G component of image data supplied thereto, control bits CTL 0  and CTL 1 , and auxiliary data supplied thereto in a time-sharing manner. That is to say, the encoder/serializer  81 B takes the G component of image data supplied thereto as parallel data in increments of 8 bits, this being the number of fixed bits. Further, the encoder/serializer  81 B encodes the parallel data thereof to convert this into serial data, and transmits this using the TMDS channel #1. 
     Also, the encoder/serializer  81 B encodes the 2-bit parallel data of the control bits CTL 0  and CTL 1  supplied thereto to convert this into serial data, and transmits this using the TMDS channel #1. Further, the encoder/serializer  81 B takes the auxiliary data supplied thereto as parallel data in increments of 4 bits. The encoder/serializer  81 B encodes the parallel data thereof to convert this into serial data, and transmits this using the TMDS channel #1. 
     The encoder/serializer  81 C transmits the R component of image data, control bits CTL 2  and CTL 3 , and auxiliary data supplied thereto in a time-sharing manner. That is to say, the encoder/serializer  81 C takes the R component of image data supplied thereto as parallel data in increments of 8 bits, this being the number of fixed bits. Further, the encoder/serializer  81 C encodes the parallel data thereof to convert this into serial data, and transmits this using the TMDS channel #2. 
     Also, the encoder/serializer  81 C encodes the 2-bit parallel data of the control bits CTL 2  and CTL 3  supplied thereto to convert this into serial data, and transmits this using the TMDS channel #2. Further, the encoder/serializer  81 C takes the auxiliary data supplied thereto as parallel data in increments of 4 bits. The encoder/serializer  81 C encodes the parallel data thereof to convert this into serial data, and transmits this using the TMDS channel #2. 
     The receiver  82  includes three recoveries/decoders  82 A,  82 B, and  82 C corresponding to the three TMDS channels #0, #1, and #2, respectively. Each of the recoveries/decoders  82 A,  82 B, and  82 C receive image data, auxiliary data, and control data transmitted using differential signals with the TMDS channels #0, #1, and #2. Further, each of the recoveries/decoders  82 A,  82 B, and  82 C converts the image data, auxiliary data, and control data from serial data to parallel data, further decodes this, and outputs this. 
     That is to say, the recovery/decoder  82 A receives the B component of image data, vertical synchronizing signal and horizontal synchronizing signal, and auxiliary data transmitted using differential signals with the TMDS channel #0. Subsequently, the recovery/decoder  82 A converts the B component of the image data, vertical signal and horizontal signal, and auxiliary data from serial data to parallel data, decodes this, and outputs this. 
     The recovery/decoder  82 B receives the G component of image data, control bits CTL 0  and CTL 1 , and auxiliary data transmitted using differential signals with the TMDS channel #1. Subsequently, the recovery/decoder  82 B converts the G component of the image data, control bits CTL 0  and CTL 1 , and auxiliary data thereof from serial data to parallel data, decodes this, and outputs this. 
     The recovery/decoder  82 C receives the R component of image data, control bits CTL 2  and CTL 3 , and auxiliary data transmitted using differential signals with the TMDS channel #2. Subsequently, the recovery/decoder  82 C converts the R component of the image data, control bits CTL 2  and CTL 3 , and auxiliary data thereof from serial data to parallel data, decodes this, and outputs this. 
       FIG. 6  illustrates an example of a transmission section (period) wherein various types of transmission data are transmitted using the three TMDS channels #0, #1, and #2 of HDMI. Note that  FIG. 6  illustrates the sections of various types of transmission data in the case that a progressive image of which the vertical×width is 720×480 pixels is transmitted with the TMDS channels #0, #1, and #2. 
     With a video field where transmission data is transmitted with the three TMDS channels #0, #1, and #2 of HDMI, there are three types of sections according to the type of transmission data; video data section (Video Data period), data island section (Data Island period), and control section (Control period). 
     Here, the video field section is a section from the leading edge (active edge) of a certain vertical synchronizing signal to the leading edge of the next vertical synchronizing signal, and is divided into a horizontal blanking period (horizontal blanking), a vertical blanking period (vertical blanking), and an active video section (Active Video) which is the video field section from which the horizontal blanking period and the vertical blanking period are removed. 
     The video data section is assigned to the active video section. During this video data section, the data of 720 pixels×480 lines worth of valid pixels (Active pixel) making up one screen worth of uncompressed image data is transmitted. 
     The data island section and the control section are assigned to the horizontal blanking period and the vertical blanking period. During this data island section and the control section, auxiliary data (Auxiliary data) is transmitted. 
     That is to say, the data island section is assigned to a portion of the horizontal blanking period and the vertical blanking period. During this data island section, of the auxiliary data, data not relating to control, e.g., a packet of audio data or the like is transmitted. 
     The control section is assigned to another portion of the horizontal blanking period and the vertical blanking period. During this control section, of the auxiliary data, data relating to control, e.g., the vertical synchronizing signal and horizontal synchronizing signal, control packet, or the like is transmitted. 
     Here, with the current HDMI, the frequency of the pixel clock transmitted with the TMDS clock channel is, for example, 165 MHz, and in this case, the transmission rate of the data island section is approximately 500 Mbps. 
       FIG. 7  illustrates the pin arrays of the HDMI terminals  211  and  251 . These pin arrays are called type A (type-A). 
     Two lines which are differential lines where TMDS Data #i+ and TMDS Data #i− serving as the differential signals of the TMDS channel #i are connected to pins to which the TMDS Data #i+ is assigned (pins of which the pin numbers are 1, 4, and 7), and pins to which the TMDS Data #i− is assigned (pins of which the pin numbers are 3, 6, and 9). 
     Also, the CEC line  84 , where the CEC signal which is data for control is transmitted, is connected to a pin of which the pin number is 13, and a pin of which the pin number is 14 is an empty (reserved) pin. Also, a line where an SDA (Serial Data) signal such as an E-EDID signal or the like is transmitted is connected to a pin of which the pin number is 16, and a line where an SCL (Serial Clock) signal that is a clock signal used for synchronization at the time of transmission/reception of the SDA signal is transmitted is connected to a pin of which the pin number is 15. The above DDC  83  is made up of a line where the SDA signal is transmitted, and a line where the SCL signal is transmitted. 
     Also, an HPD line  86  used for a source device detecting connection of a sink device as described above is connected to a pin of which the pin number is 19. Also, a line  87  used for supplying power as described above is connected to a pin of which the pin number is 18. 
       FIG. 8  illustrates a configuration example of the high-speed data line interface  213  of the disk recorder  210 , and the high-speed data line interface  253  of the television receiver  250 . These interface  213  and  253  make up a communication unit configured to execute LAN (Local Area Network) communication. This communication unit executes bidirectional communication using, of the multiple lines making up the HDMI cable  350 , a pair of differential lines, and with the present embodiment, a reserve line (Ether− line) corresponding to an empty (reserve) pin (pin  14 ), and an HPD line (Ether+ line) corresponding to the HPD pin (pin  19 ). 
     The disk recorder  210  includes a LAN signal transmission circuit  411 , a terminating resistor  412 , an AC coupling capacitances  413  and  414 , a LAN signal reception circuit  415 , and a subtraction circuit  416 , which make up the high-speed data line interface  213 . 
     A series circuit of the AC coupling capacitance  413 , terminating resistor  412 , and AC coupling capacitance  414  is connected between the pin  14  and pin  19  of the HDMI terminal  211 . A mutual connection point P 1  of the AC coupling capacitance  413  and the terminating resistor  412  is connected to the positive output side of the LAN signal transmission circuit  411 , and is also connected to the positive input side of the LAN signal reception circuit  415 . Also, a mutual connection point P 2  of the AC coupling capacitance  414  and the terminating resistor  412  is connected to the negative output side of the LAN signal transmission circuit  411 , and is also connected to the negative input side of the LAN signal reception circuit  415 . The input side of the LAN signal transmission circuit  411  is supplied with a transmission signal (transmission data) SG 411 . 
     Also, the positive side terminal of the subtraction circuit  416  is supplied with the output signal SG 412  of the LAN signal reception circuit  415 , and the negative side terminal of this subtraction circuit  416  is supplied with a transmission signal (transmission data) SG 411 . With this subtraction circuit  416 , the transmission signal SG 411  is subtracted from the output signal SG 412  of the LAN signal reception circuit  415 , and a reception signal (reception data) SG 413  is obtained. 
     The television receiver  250  includes a LAN signal transmission circuit  441 , a terminating resistor  442 , an AC coupling capacitances  443  and  444 , a LAN signal reception circuit  445 , and a subtraction circuit  446 , which make up the high-speed data line interface  253 . Also, the television receiver  250  includes pull-up resistors  447  and  448 . 
     A series circuit of the AC coupling capacitance  443 , terminating resistor  442 , and AC coupling capacitance  444  is connected between the pin  14  and pin  19  of the HDMI terminal  251 . A mutual connection point P 3  of the AC coupling capacitance  443  and the terminating resistor  442  is connected to the positive output side of the LAN signal transmission circuit  441 , and is also connected to the positive input side of the LAN signal reception circuit  445 . Also, a mutual connection point P 4  of the AC coupling capacitance  444  and the terminating resistor  442  is connected to the negative output side of the LAN signal transmission circuit  441 , and is also connected to the negative input side of the LAN signal reception circuit  445 . The input side of the LAN signal transmission circuit  441  is supplied with a transmission signal (transmission data) SG 417 . 
     Also, the positive side terminal of the subtraction circuit  446  is supplied with the output signal SG 418  of the LAN signal reception circuit  445 , and the negative side terminal of this subtraction circuit  446  is supplied with a transmission signal (transmission data) SG 417 . With this subtraction circuit  446 , the transmission signal SG 417  is subtracted from the output signal SG 418  of the LAN signal reception circuit  445 , and a reception signal (reception data) SG 419  is obtained. 
     The pin  19  of the HDMI terminal  251  is connected to a power supply line (+5.0V) via a pull-up resistor  447 . Also, this television receiver  250  is an eHDMI-compatible device, and accordingly, the pin  14  of the HDMI terminal  251  is connected to the power supply line (+5.0V) via the pull-up resistor  448 . 
     A reserve line  501  and an HPD line  502  included in the HDMI cable  350  make up a differential twist pair. The source side edge  511  of the reserve line  501  is connected to the  14  pin of the HDMI terminal  211 , and the sink side edge  521  of this reserve line  501  is connected to the  14  pin of the HDMI terminal  251 . Also, the source side edge  512  of the HPD line  502  is connected to the  19  pin of the HDMI terminal  211 , and the sink side edge  522  of this HPD line  502  is connected to the  19  pin of the HDMI terminal  251 . 
     Next, the operation of LAN communication with the high-speed data line interfaces  213  and  253  configured as described above will be described. 
     With the disk recorder  210 , the transmission signal (transmission data) SG 411  is supplied to the input side of the LAN signal transmission circuit  411 , and the differential signals corresponding to the transmission signal SG 411  (positive output signal, negative output signal) are output from this LAN signal transmission circuit  411 . Subsequently, the differential signals output from the LAN signal transmission circuit  411  are supplied to the connection points P 1  and P 2 , and are transmitted to the television receiver  250  via the pair line of the HDMI cable  350  (reserve line  501 , HPD line  502 ). 
     Also, with the television receiver  250 , the transmission signal (transmission data) SG 417  is supplied to the input side of the LAN signal transmission circuit  441 , and the differential signals corresponding to the transmission signal SG 417  (positive output signal, negative output signal) are output from this LAN signal transmission circuit  441 . Subsequently, the differential signals output from the LAN signal transmission circuit  441  are supplied to the connection points P 3  and P 4 , and are transmitted to the disk recorder  210  via the pair line of the HDMI cable  350  (reserve line  501 , HPD line  502 ). 
     Also, with the disk recorder  210 , the input side of the LAN signal reception circuit  415  is connected to the connection points P 1  and P 2 , and accordingly, an addition signal is obtained from the transmission signal corresponding to the differential signal (current signal) output from the LAN signal transmission circuit  411 , and the reception signal corresponding to the differential signal to be transmitted from the television receiver  250  as described above, as the output signal SG 412  of this LAN signal reception circuit  415 . With the subtraction circuit  416 , the transmission signal SG 411  is subtracted from the output signal SG 412  of the LAN signal reception circuit  415 . Therefore, the output signal SG 413  of this subtraction circuit  416  corresponds to the transmission signal (transmission data) SG 417  of the television receiver  250 . 
     Also, with the television receiver  250 , the input side of the LAN signal reception circuit  445  is connected to the connection points P 3  and P 4 , and accordingly, an addition signal is obtained from the transmission signal corresponding to the differential signal (current signal) output from the LAN signal transmission circuit  441 , and the reception signal corresponding to the differential signal to be transmitted from the disk recorder  210  as described above, as the output signal SG 418  of this LAN signal reception circuit  445 . With the subtraction circuit  446 , the transmission signal SG 417  is subtracted from the output signal SG 418  of the LAN signal reception circuit  445 . Therefore, the output signal SG 419  of this subtraction circuit  446  corresponds to the transmission signal (transmission data) SG 411  of the disk recorder  210 . 
     Thus, bidirectional LAN communication can be executed between the high-speed data line interface  213  of the disk recorder  210 , and the high-speed data line interface  253  of the television receiver  250 . 
     Note that, with the television receiver  250 , the pin  19  of the HDMI terminal  251  is connected to the power supply line (+5.0V). Therefore, when the television receiver  250  is connected to the disk recorder  210  via the HDMI cable  350 , the voltage Vhpd at the pin  19  of the HDMI terminal  211  increases. Accordingly, with the disk recorder  210 , whether or not the television receiver  250  has been connected to the disk recorder  210  via the HDMI cable  350  can be detected by monitoring the voltage Vrsv at the pin  19  of the HDMI terminal  211 . 
     Also, with the television receiver  250 , the pin  14  of the HDMI terminal  251  is connected to the power supply line (+5.0V). Therefore, when the television receiver  250  is connected to the disk recorder  210  via the HDMI cable  350 , the voltage Vhpd at the pin  14  of the HDMI terminal  211  increases. Accordingly, with the disk recorder  210 , whether or not the television receiver  250  is an eHDMI-compatible device can be recognized by monitoring the voltage Vhpd at the pin  14  of the HDMI terminal  211 . 
     With the present embodiment, the television receiver  250  can recognize that the disk recorder  210  is an eHDMI-compatible device. The technique thereof will be described below. 
     For example, when the television receiver  250  is connected to the disk recorder  210  via the HDMI cable  350 , the disk recorder  210  transmits function information indicating that it itself is an eHDMI-compatible device, i.e., includes a communication unit (high-speed data line interface  213  or the like) using a communication path made up of the reserve line and the HPD line of the HDMI cable  350 , to the television receiver  250 . Also, the disk recorder  210  includes transmission format (application) information that the disk recorder  210  can support in this function information. 
     Here, the transmission format information is information regarding whether supporting only the SPDIF (Sony Philips Digital InterFace) signal, or supporting only the Ethernet signal, or supporting both of the SPDIF signal and the Ethernet signal. 
     Now, the SPDIF signal will be described briefly. This SPDIF signal is a signal to be transmitted with the SPDIF standard. The SPDIF standard is an interface standard used for transmitting digital audio signals in real time. The SPDIF signal is subjected to biphase mark modulation, and accordingly, includes a clock component within the signal thereof. 
     Note that the configuration example of the above  FIG. 8  illustrates the case where only the Ethernet signal is supported. In the case of also supporting the SPDIF signal, the configuration example thereof is such as shown in  FIG. 9 . The television receiver  250  includes a SPDIF transmission circuit  449 . The SPDIF signal output from this SPDIF transmission circuit  449  is transmitted to the disk recorder  210  side with the same phase by adders  451  and  452  using the reserve line and the HPD line making up the HDMI cable  350 . Here, the SPDIF transmission circuit  449  makes up, in the same way as with the high-speed data line interface  253 , a communication unit configured to execute communication using a communication path made up of the reserve line and the HPD line. 
     Also, the disk recorder  210  includes a SPDIF reception circuit  417 . The SPDIF signal transmitted with the same phase from the television receiver  250  side with the reserve line and the HPD line making up the HDMI cable  350  is added at the adder  421 , and is supplied to the SPDIF reception circuit  417 . Here, the SPDIF reception circuit  417  makes up, in the same way as with the high-speed data line interface  213 , a communication unit configured to execute communication using a communication path made up of the reserve line and the HPD line. 
     Note that, in the case of supporting only the SPDIF signal, with the configuration example shown in  FIG. 9 , the configuration is changed by removing the high-speed data interfaces  213  and  253  therefrom. 
     For example, the disk recorder  210  inserts the above function information during the blanking period of the video signal to be transmitted to the television receiver  250  with the above TMDS channel, thereby transmitting this function information to the television receiver  250 . Here, the disk recorder  210  uses, for example, the AVI (Auxiliary Video Information) InfoFrame packet of the HDMI to insert the above function information during the blanking period of the video signal. 
     This AVI InfoFrame packet is disposed during the above data island section.  FIG. 10  illustrates the data structure of the AVI InfoFrame packet. With HDMI, according to this AVI InfoFrame packet, auxiliary information relating to an image can be transmitted from a source device to a sink device. 
     With the present embodiment, the function information is disposed, such as shown in the data structure of the AVI InfoFrame in  FIG. 10 , in one bit of E1 at the fourth byte (Data Byte 1), and two bits of E2 and E3 at the eighth byte (Data Byte 5) in a hierarchical manner. 
     E1 that is 1-bit data is data for identifying whether or not an eHDMI-compatible device including a communication unit (high-speed data line interface  213 , SPDIF reception circuit  417 ) configured to execute communication via a communication path made up of the reserve line and the HPD line of the HDMI cable  350 . Here, when E1=0, this indicates not being eHDMI-compatible, and when E1=1, this indicates being eHDMI-compatible. 
     Also, E2 and E3 that are 2-bit data are bit data for identifying whether supporting only the SPDIF signal, supporting only the Ethernet signal, or supporting both the SPDIF signal and the Ethernet signal. For example, when E2=1, and E3=0, this indicates supporting only the SPDIF signal, and when E2=0, and E3=1, this indicates supporting only the Ethernet signal, and when E2=1, and E3=1, this indicates supporting both of the SPDIF signal and the Ethernet signal. 
     In the case that the disk recorder  210  inserts the function information during the blanking period of the video signal to be transmitted to the television receiver  250  with the TMDS channel as described above, thereby transmitting this function information to the television receiver  250 , the television receiver  250  receives this function information by extracting the above function information from the blanking period of the video signal received from the disk recorder  210  with the TMDS channel. 
     Note that the above description has shown the case where the function information is inserted during the blanking period of a video signal using the AV InfoFrame packet. Though detailed description will be omitted, the function information may be inserted during the blanking period of a video signal even using other packets such as a GCP packet or the like. 
     Also, for example, the disk recorder  210  transmits the above function information to the television receiver  250  via the CEC line  84  which is the control data line of the HDMI cable  350 . In this case, the television receiver  250  receives the function information from the disk recorder  210  via the CEC line  84 . 
     The television receiver  250  receives the function information as described above, whereby whether or not the disk recorder  210  is an eHDMI-compatible device can be recognized, and in the case of an eHDMI-compatible device, the transmission format (application) that the disk recorder  210  can support can be recognized. Note that, as described above, in the case that the function information is transmitted from the disk recorder  210  to the television receiver  250 , the HDMI transmission unit  212  of the disk recorder  210  makes up a function information transmission unit, and the HDMI reception unit  252  of the television receiver  250  makes up a function information reception unit. 
     Note that the above description has shown the case where the television receiver  250  is connected to the disk recorder  210  via the HDMI cable  350 , the disk recorder  210  automatically transmits the function information to the television receiver  250 . However, an arrangement may be made wherein a transmission request for this function information is transmitted from the television receiver  250  side to the disk recorder  210 , and when receiving this transmission request, the disk recorder  210  transmits the function information to the television receiver  250 . 
     For example, when the television receiver  250  executes switching of HDMI input at the time of power-on, or the like, the television receiver  250  transmits this transmission request to the disk recorder  210  via the CEC line  84 . In this case, the HDMI reception unit  253  of the television receiver  250  makes up a function information requesting unit, and the HDMI transmission unit  213  of the disk recorder  210  makes up a transmission request reception unit. 
     Thus, in the case that the television receiver  250  transmits a transmission request to the disk recorder  210 , the television receiver  250  can confirm at arbitrary timing (e.g., at the time of power-on, at the time of input switching, or the like) whether or not the disk recorder  210  is an eHDMI-compatible device, and further the transmission format (application) that the disk recorder  210  can support can be confirmed. 
     The above description has shown an example wherein the function information is transmitted from the disk recorder  210  to the television receiver  250 . Conversely, it can be conceived that the function information is transmitted from the television receiver  250  to the disk recorder  210 , in the same way as described above. In this case, the function information cannot be transmitted by inserting this during the blanking period of a video signal, but the function information can transmit via the CEC line  84  which is the control data line. In this case, the HDMI transmission unit  212  of the disc recorder  210  makes up a function information reception unit, and the HDMI reception unit  252  of the television receiver  250  makes up a function information transmission unit. 
     Now, transmission/reception of the function information using the CEC line (CEC channel) will be described. With this CEC line, transmission of control data can be executed bidirectionally between a source device and a sink device. With the present invention, the above function information is transmitted from a source device to a sink device, or from a sink device to a source device as the CEC (Consumer Electronics Control) data or CDC (Capability Discovery Channel) data. 
       FIG. 11  illustrates the structure of CEC data to be transmitted with the CEC line. With the CEC line, one block made up of 10-bit data is transmitted for 4.5 milliseconds. A start bit is disposed at the head, subsequently thereto, a header block is disposed, and thereafter, an arbitrary number (n) of data blocks including desired data to be transmitted are disposed. The function information is included in the data blocks. 
       FIG. 12  is a diagram illustrating a structure block of the header block. With the header block, the logical address (Logical Address) of a source (Initiator), and the logical address (Logical Address) of a destination (Destination) are disposed. Each logical address is set according to the type of each device. 
       FIG. 13  illustrates logical addresses to be set according to the type of each device. As shown in  FIG. 13, 16  types of address values from “0” to “15” are set for each type of device. With the logical address of a source (Initiator) and the logical address of a destination (Destination) making up the header block in  FIG. 12 , the corresponding address values are disposed with four bits. 
     Next, the CDC data will be described. The CDC is defined so as to have the same physical layer as the CEC, but so as to have a logical layer different from the CEC. The structure of the CDC data is not shown in the drawing, but is of the same data structure as the data structure of the CEC shown in  FIG. 11 , wherein a start bit is disposed at the head, subsequently thereto, a header block is disposed, and thereafter, an arbitrary number (n) of data blocks including desired data to be transmitted are disposed. 
     Also, the structure of the header block of the CDC data is not shown in the drawing, but is the same as the header block of the CEC data shown in  FIG. 12  structurally. However, “15” is constantly used as the logical address of a source (Initiator), and the logical address of a destination (Destination) making up the header block, regardless of the type of device. That is to say, with regard to a source (Initiator), unknown (Unregistered) is used, and with regard to a destination (Destination), broadcast (Broadcast) is used. 
     Thus, with the transmission of the CDC data, “15” is used as the logical addresses (Logical Address) of an initiator and a destination to be disposed in the head block, and accordingly, the logical address of each device does not have to be obtained. The message according to the CDC data (CDC message) is a broadcast message of which the initiator is unknown for the CEC, and accordingly, from which device to which device this message is addressed is not known. 
     Therefore, with the CDC message, in order to identify a physical connection path, the physical addresses (Physical Address) of a source (Initiator) and a destination (Target) are included without fail in a message to be disposed in the data block. That is to say, at the time of transmission of the CDC message, logical addresses are not used, and physical addresses are used. 
     With the CEC, a message to the effect that &lt;Feature Abort&gt;“it is incompatible” cannot be returned regarding broadcast messages. Therefore, this situation is taken into consideration, and accordingly, let us say that a message is returned without fail as the CDC. 
     [CDC Message] 
     Here, as command messages to be disposed in the data block of the CDC data, an &lt;Exchange Supported Channels Info&gt; message, and an &lt;Activate Supported Channels&gt; message are defined. The &lt;Exchange Supported Channels Info&gt; message is a message used at the time of exchanging the function information between two devices. Also, the &lt;Activate Supported Channels&gt; message is a message used at the time of confirming a channel (transmission format) to be activated actually between two devices, and starting communication. Each message has a data structure such as the following. 
     
       
         
           
               
             
               
                 TABLE 1 
               
               
                   
               
             
            
               
                 &lt;Exchange Supported Channels Info&gt; 
               
            
           
           
               
               
               
               
            
               
                 [Physical Address] 
                 2 
                 bytes 
                 PA of Initiator 
               
               
                 [Physical Address] 
                 2 
                 bytes 
                 PA of Target 
               
               
                 [Supported Channels] 
                 1 
                 byte 
               
               
                 [Audio Return Channel] 
                 1 
                 bit 
                 if initiator supports this channel, set this “1”, else “0”. 
               
               
                 [Ethernet Channel] 
                 1 
                 bit 
                 if initiator supports this channel, set this “1”, else “0”. 
               
               
                 [reserved] 
                 6 
                 bits (=000000) 
               
            
           
           
               
            
               
                 &lt;Activate Supported Channels&gt; 
               
            
           
           
               
               
               
               
            
               
                 [Physical Address] 
                 2 
                 bytes 
                 PA of Initiator 
               
               
                 [Physical Address] 
                 2 
                 bytes 
                 PA of Target 
               
               
                 [Supported Channels] 
                 1 
                 byte 
               
               
                 [Audio Return Channel] 
                 1 
                 bit 
                 if initiator wants to activate this channel, set this “1”. 
               
               
                   
                   
                   
                 if initiator wants to de-activate this channel, set this “0”. 
               
               
                 [Ethernet Channel] 
                 1 
                 bit 
                 if initiator wants to activate this channel, set this “1”. 
               
               
                   
                   
                   
                 if initiator wants to de-activate this channel, set this “0”. 
               
               
                 [reserved] 
                 6 
                 bits (=000000) 
               
               
                   
               
            
           
         
       
     
     The &lt;Exchange Supported Channels Info&gt; message will be described. This &lt;Exchange Supported Channels Info&gt; message has data of five bytes of a first byte through a fifth byte. The physical address (Physical Address) of a source (Initiator) is disposed in the first and second byte, and the physical address (Physical Address) of a destination (Target) is disposed in the third and fourth bytes. 
     Also, the function information of the source (Initiator) is disposed in the fifth byte. This function information is information indicating that it itself is an eHDMI-compatible device, and includes a channel that it itself can support, i.e., the information of a transmission format (application) that the it can support itself. 
     One bit of the fifth byte, e.g., the seventh bit (most significant bit) indicates that it itself is an eHDMI-compatible device, and whether or not supporting the transmission format (application) of the above SPDIF signal, i.e., whether or not supporting the [Audio Return Channel]. One bit of the fifth byte is set to “1” when supporting this, and is set to “0” when not supporting this. 
     Also, another one bit of the fifth byte, e.g., the sixth bit indicates that it itself is an eHDMI-compatible device, and whether or not supporting the transmission format (application) of the Ethernet signal, i.e., whether or not supporting the [Ethernet Channel]. Another one bit of the fifth byte is set to “1” when supporting this, and is set to “0” when not supporting this. 
     Also, the remaining six bits of the fifth byte, e.g., the fifth bit through the zero&#39;th bit are set to reserved bits, and are all set to “0”. 
     Next, the &lt;Activate Supported Channels&gt; message will be described. This &lt;Activate Supported Channels&gt; message includes data of five bytes of the first byte through the fifth byte. The physical address (Physical Address) of a source (Initiator) is disposed in the first and second byte, and the physical address (Physical Address) of a destination (Target) is disposed in the third and fourth bytes. 
     Also, the information of a channel (transmission format) that the source (Initiator) asks for activation is disposed in the fifth byte. One bit of the fifth byte, e.g., the seventh bit indicates whether or not it itself asks for communication of the SPDIF signal, i.e., activation of the channel of the [Audio Return Channel]. One bit of this fifth byte is set to “1” when asking for activation, and is set to “0” when not asking for activation. 
     Also, another one bit of the fifth byte, e.g., the sixth bit indicates whether or not it itself asks for communication of the Ethernet signal, i.e., activation of the channel of the [Ethernet Channel]. Another one bit of the fifth byte is set to “1” when asking for activation, and is set to “0” when not asking for activation. 
     Also, the remaining six bits of the fifth byte, e.g., the fifth bit through the zero&#39;th bit are set to reserved bits, and are all set to “0”. 
     The rule of the above &lt;Exchange Supported Channels Info&gt; message and &lt;Activate Supported Channels&gt; message are defined such as the following. That is to say, when a certain CDC device broadcasts the &lt;Exchange Supported Channels Info&gt; message, the CDC device having the physical address of a destination included in the message thereof broadcasts the &lt;Exchange Supported Channels Info&gt; message including the information (parameters) of itself. 
     Also, when a certain CDC device broadcasts the &lt;Activate Supported Channels&gt; message, the CDC device having the physical address (Physical Address) of a destination included in the message thereof broadcasts the &lt;Activate Supported Channels&gt; message including the information (parameters) of itself. Further, with the function information exchanged with the &lt;Exchange Supported Channels Info&gt; message, of the channels of the [Audio Return Channel] and the [Ethernet Channel], when there is a channel (transmission format) supported by both, communication by the channel thereof can be executed between two devices. 
     Note that the CDC device means an eHDMI-compatible device that can support CDC data &lt;Exchange Supported Channels Info&gt; message, &lt;Activate Supported Channels&gt; message, and the like. On the other hand, the Non-CDC device means an eHDMI-compatible device that cannot support CDC data &lt;Exchange Supported Channels Info&gt; message, &lt;Activate Supported Channels&gt; message, and the like. 
     [Exchange Sequence] 
     Next, an example of use of the &lt;Exchange Supported Channels Info&gt; message will be described with reference to the sequence diagram in  FIG. 14 . Note that this case assumes an AV system  10  of the device configuration shown in  FIG. 15 . That is to say, the AV system  10  is configured of CDC devices  11  and  12 , and a Non-CDC device  13 . The HDMI terminal  11   a  of the CDC device  11 , and the HDMI terminal  12   a  of the CDC device  12  are connected via an HDMI cable  14 . Also, the HDMI terminal  11   b  of the CDC device  11 , and the HDMI terminal  13   a  of the Non-CDC device  13  are connected via an HDMI cable  15 . Also, the physical address (Physical Address) of the CDC device  11  is [0.0.0.0], the physical address (Physical Address) of the CDC device  12  is [1.0.0.0], and the physical address (Physical Address) of the Non-CDC device  13  is [2.0.0.0]. 
     Returning to  FIG. 14 , (a) the CDC device  11  broadcasts the &lt;Exchange Supported Channels Info&gt; message to exchange the function information with the CDC device  12 . The physical address of the source (Initiator) is set to [0.0.0.0], and the physical address of the destination (Target) is set to [1.0.0.0], which are included in the &lt;Exchange Supported Channels Info&gt; message. Also, the CDC device  11  includes the function information of itself in the &lt;Exchange Supported Channels Info&gt; message. For example, this &lt;Exchange Supported Channels Info&gt; message indicates that both channels of the [Audio Return Channel] and the [Ethernet Channel] are supported. 
     (b) The CDC device  12  broadcasts the &lt;Exchange Supported Channels Info&gt; message since the physical address of a destination included in the &lt;Exchange Supported Channels Info&gt; message broadcasted from the CDC device  11  is the physical address [1.0.0.0] of itself. The physical address of the source (Initiator) is set to [1.0.0.0], and the physical address of the destination (Target) is set to [0.0.0.0], which are included in the &lt;Exchange Supported Channels Info&gt; message. Also, the CDC device  12  includes the function information of itself in the &lt;Exchange Supported Channels Info&gt; message. For example, this &lt;Exchange Supported Channels Info&gt; message indicates that both channels of the [Audio Return Channel] and the [Ethernet Channel] are supported. 
     Thus, the &lt;Exchange Supported Channels Info&gt; message is transmitted/received between the CDC device  11  and the CDC device  12 , whereby the mutual function information, i.e., information indicating whether or not an eHDMI-compatible device, and whether or not the [Audio Return Channel] or [Ethernet Channel] is supported, is exchanged. 
     (C) The CDC device  11  broadcasts the &lt;Exchange Supported Channels Info&gt; message to exchange the function information with the Non-CDC device  13 . The physical address of the source (Initiator) is set to [0.0.0.0], and the physical address of the destination (Target) is set to [2.0.0.0], which are included in the &lt;Exchange Supported Channels Info&gt; message. Also, the CDC device  11  includes the function information of itself in the &lt;Exchange Supported Channels Info&gt; message. For example, this &lt;Exchange Supported Channels Info&gt; message indicates that both channels of the [Audio Return Channel] and the [Ethernet Channel] are supported. 
     (d) The Non-CDC device  13  does not react at all even if the physical address of a destination included in the &lt;Exchange Supported Channels Info&gt; message broadcasted from the CDC device  11  is the physical address [2.0.0.0] of itself. In this case, with a 2-second limiting rule, when there has been no reaction even if two seconds elapses, the CDC device  11  recognizes that the Non-CDC device  13  does not support both channels of the [Audio Return Channel] and the [Ethernet Channel]. 
     [Active/Inactive Sequence] 
     Next, an example of use of the &lt;Active Supported Channels&gt; message will be described with reference to the sequence diagram in  FIG. 16 . Note that this case assumes a case where, with the AV system  10  having the device configuration shown in  FIG. 15 , as described above, communication is executed between the CDC device  11  and the CDC device  12  which have exchanged the function information using the &lt;Exchange Supported Channels Info&gt; message. 
     (a) The CDC device  11  broadcasts the &lt;Active Supported Channels&gt; message to confirm the channel (transmission format) to be asked for activation actually so as to start communication with the CDC device  12 . The physical address of the source (Initiator) is set to [0.0.0.0], and the physical address of the destination (Target) is set to [1.0.0.0], which are included in this &lt;Active Supported Channels&gt; message. Also, the CDC device  11  disposes the information of the channel (transmission format) which it itself asks for activation, in this &lt;Active Supported Channels&gt; message. For example, this &lt;Active Supported Channels&gt; message indicates that activation for both channels of the [Audio Return Channel] and the [Ethernet Channel] is requested. 
     (b) The CDC device  12  broadcasts the &lt;Active Supported Channels&gt; message since the physical address of the destination included in the &lt;Active Supported Channels&gt; message broadcasted from the CDC device  11  is the physical address [1.0.0.0] of itself. The physical address of the source (Initiator) is set to [1.0.0.0], and the physical address of the destination (Target) is set to [0.0.0.0], which are included in this &lt;Active Supported Channels&gt; message. Also, the CDC device  12  disposes the information of the channel (transmission format) wherein it itself agrees with the request for activation, in this &lt;Active Supported Channels&gt; message. For example, this &lt;Active Supported Channels&gt; message indicates that the request for activation of both channels of the [Audio Return Channel] and the [Ethernet Channel] is approved. 
     Thus, the &lt;Active Supported Channels&gt; message is transmitted/received between the CDC device  11  and the CDC device  12 , whereby both of the CDC device  11  and the CDC device  12  confirm the channel (transmission format) which can be shared and activated, and communication is started. With the example in  FIG. 16 , both of the CDC device  11  and the CDC device  12  can activate the [Audio Return Channel] and the [Ethernet Channel], and accordingly, both channels (transmission formats) are activated, and communication is started. 
     (c) Subsequently, for example, in the case of intending to stop the communication of the [Ethernet Channel] to execute Ethernet communication via a network terminal, the CDC device  12  broadcasts the &lt;Active Supported Channels&gt; message. The physical address of the source (Initiator) is set to [1.0.0.0], and the physical address of the destination (Target) is set to [0.0.0.0], which are included in this &lt;Active Supported Channels&gt; message. Also, this &lt;Active Supported Channels&gt; message indicates that the channel (transmission format) which the CDC device  12  itself asks for activation is the channel of the [Audio Return Channel], and the channel of the [Ethernet Channel] is removed. 
     (d) The CDC device  11  broadcasts the &lt;Active Supported Channels&gt; message since the physical address of the destination included in the &lt;Active Supported Channels&gt; message broadcasted from the CDC device  12  is the physical address [0.0.0.0] of itself. The physical address of the source (Initiator) is set to [0.0.0.0], and the physical address of the destination (Target) is set to [1.0.0.0], which are included in this &lt;Active Supported Channels&gt; message. Also, the CDC device  11  disposes the information of the channel (transmission format) wherein it itself agrees with the request for activation in this &lt;Active Supported Channels&gt; message. For example, this &lt;Active Supported Channels&gt; message indicates that the request for activation of the channel of the [Audio Return Channel] is approved. 
     Thus, the &lt;Active Supported Channels&gt; message is transmitted/received between the CDC device  11  and the CDC device  12 , whereby both of the CDC device  11  and the CDC device  12  reconfirm the channel (transmission format) which can be shared and activated, communication with the channel of the [Ethernet Channel] is stopped, and only communication with the channel of the [Audio Return Channel] is continued. 
     Next, another example of use of the &lt;Active Supported Channels&gt; message will be described with reference to the sequence diagram in  FIG. 17 . Note that this case assumes a case where, with the AV system  10  having the device configuration shown in  FIG. 15 , as described above, communication is executed between the CDC device  11  and the CDC device  12  which have exchanged the function information using the &lt;Exchange Supported Channels Info&gt; message. 
     (a) The CDC device  11  broadcasts the &lt;Active Supported Channels&gt; message to confirm the channel (transmission format) to be asked for activation actually so as to start communication with the CDC device  12 . The physical address of the source (Initiator) is set to [0.0.0.0], and the physical address of the destination (Target) is set to [1.0.0.0], which are included in this &lt;Active Supported Channels&gt; message. Also, the CDC device  11  disposes the information of the channel (transmission format) which it itself asks for activation, in this &lt;Active Supported Channels&gt; message. For example, this &lt;Active Supported Channels&gt; message indicates that activation for both channels of the [Audio Return Channel] and the [Ethernet Channel] is requested. 
     (b) The CDC device  12  broadcasts the &lt;Active Supported Channels&gt; message since the physical address of the destination included in the &lt;Active Supported Channels&gt; message broadcasted from the CDC device  11  is the physical address [1.0.0.0] of itself. The physical address of the source (Initiator) is set to [1.0.0.0], and the physical address of the destination (Target) is set to [0.0.0.0], which are included in this &lt;Active Supported Channels&gt; message. Also, the CDC device  12  disposes the information of the channel (transmission format) wherein it itself agrees with the request for activation, in this &lt;Active Supported Channels&gt; message. For example, this &lt;Active Supported Channels&gt; message indicates that the request for activation of the channel of the [Audio Return Channel] is approved. 
     Thus, the &lt;Active Supported Channels&gt; message is transmitted/received between the CDC device  11  and the CDC device  12 , whereby both of the CDC device  11  and the CDC device  12  confirm the channel (transmission format) which can be shared and activated, and communication is started. With the example in  FIG. 16 , the CDC device  11  asks for activation of both channels of the [Audio Return Channel] and the [Ethernet Channel], but the CDC device  12  agrees with activation of only the channel of the [Audio Return Channel], and accordingly, only the channel of the [Audio Return Channel] is activated, and communication is started. 
     Note that transmission/reception of the above &lt;Active Supported Channels&gt; message is executed, for example, after exchange of the function information is executed using the &lt;Exchange Supported Channels Info&gt; message, and both of the functions are known each other. Thereafter, transmission/reception of the &lt;Active Supported Channels&gt; message is executed at arbitrary timing, such as at the time of change of the desired channel for communication, or the like. 
     [Improvement of Validity of CDC Message] 
     As described above, the physical addresses (Physical Address) of the source (Initiator) and the destination (Target) are arranged to be included in the CDC message without fail. For example, in the case that a sink device includes multiple HDMI terminals, with a source device connected to a predetermined port (HDMI terminal) where the HPD signal is “L”, the physical address (Physical Address) thereof is unfixed. Thus, when the physical address is unfixed, the validity of the above CDC message decreases. Therefore, in such a case, an example wherein improvement of the validity of the CDC message is realized will be described below. 
     Example 1 
     With this example 1, a direct mode (Direct Mode) bit is provided to the &lt;Active Supported Channels&gt; message and the &lt;Exchange Supported Channels Info&gt; message, thereby realizing improvement of the validity of the CDC message. In this case, the &lt;Exchange Supported Channels Info&gt; message and the &lt;Active Supported Channels&gt; message have a data structure, for example, such as shown in the following. 
     
       
         
           
               
             
               
                 TABLE 2 
               
               
                   
               
             
            
               
                 &lt;Exchange Supported Channels Info&gt; 
               
            
           
           
               
               
               
               
            
               
                 [Physical Address] 
                 2 
                 bytes 
                 PA of Initiator 
               
               
                 [Physical Address] 
                 2 
                 bytes 
                 PA of Target 
               
               
                 [Supported Capabilities] 
                 1 
                 byte 
               
               
                 [Direct Mode] 
                 1 
                 bit 
                 if initiator supports communication in HPD = L set this “1”, else “0”. 
               
               
                 [Audio Return Channel] 
                 1 
                 bit 
                 if initiator supports Audio Return Channel, set this “1”, else “0”. 
               
               
                 [Ethernet Channel] 
                 1 
                 bit 
                 if initiator supports Ethernet Communication, set this “1”, else “0”. 
               
               
                 [reserved] 
                 5 
                 bits (=00000) 
               
            
           
           
               
            
               
                 &lt;Activate Supported Channels&gt; 
               
            
           
           
               
               
               
               
            
               
                 [Physical Address] 
                 2 
                 bytes 
                 PA of Initiator 
               
               
                 [Physical Address] 
                 2 
                 bytes 
                 PA of Target 
               
               
                 [Supported Capabilities] 
                 1 
                 byte 
               
               
                 [Direct Mode] 
                 1 
                 bit 
                 indicate Direct Mode (1) or not (0) 
               
               
                 [Audio Return Channel] 
                 1 
                 bit 
                 if initiator wants to activate Audio Return Channel, set this “1”. 
               
               
                   
                   
                   
                 if initiator wants to de-activate Audio Return Channel, set this “0”. 
               
               
                 [Ethernet Channel] 
                 1 
                 bit 
                 if initiator wants to activate Ethernet Communication, set this “1”. 
               
               
                   
                   
                   
                 if initiator wants to de-activate Ethernet Communication set this “0”. 
               
               
                 [reserved] 
                 5 
                 bits (=00000) 
               
               
                   
               
            
           
         
       
     
     The &lt;Exchange Supported Channels Info&gt; message will be described. This &lt;Exchange Supported Channels Info&gt; message includes data of five bytes of the first byte through the fifth byte. The physical address (Physical Address) of a source (Initiator) is disposed in the first and second bytes, and the physical address (Physical Address) of a destination (Target) is disposed in the third and fourth bytes. 
     Also, the function information of the source (Initiator) is disposed in the fifth byte. This function information has information indicating that it itself supports the direct mode. Also, this function information has information indicating that it itself is an eHDMI-compatible device, and includes the information of the channel that it can support itself. That is to say, one bit of the fifth byte, for example, the seventh bit indicates whether or not supporting the direct mode. One bit of this fifth byte is set to “1” when supporting the direct mode, and is set to “0” when not supporting the direct mode. 
     Also, another one bit of the fifth byte, for example, the sixth bit indicates that it itself is an eHDMI-compatible device, and supports the above SPDIF signal, i.e., whether or not supporting the [Audio Return Channel]. Another bit of the fifth byte is set to “1” when supporting the [Audio Return Channel], and is set to “0” when not supporting the [Audio Return Channel]. 
     Also, another one bit of the fifth byte, for example, the fifth bit indicates that it itself is an eHDMI-compatible device, and whether or not supporting the above Ethernet signal, i.e., whether or not supporting the [Ethernet Channel]. Another bit of the fifth byte is set to “1” when supporting the [Ethernet Channel], and is set to “0” when not supporting the [Ethernet Channel]. Also, the remaining five bits of the fifth byte, e.g., the fourth bit through the zero&#39;th bit are set to reserved bits, and are all set to “0”. 
     Next, the &lt;Active Supported Channels&gt; message will be described. This &lt;Active Supported Channels&gt; message includes data of five bytes of the first byte through the fifth byte. The physical address (Physical Address) of a source (Initiator) is disposed in the first and second bytes, and the physical address (Physical Address) of a destination (Target) is disposed in the third and fourth bytes. Also, information indicating whether or not this message is a message according to the direct mode, and the information of a channel (transmission format) which the source (Initiator) asks for activation, is disposed in the fifth byte. 
     That is to say, one bit of the fifth byte, e.g., the seventh bit indicates whether or not this message is a message according to the direct mode. This one bit of the fifth byte is set to “1” at the time of a message according to the direct mode, and is set to “0” at the time of not a message according to the direct mode but a common message. Another one bit of the fifth byte, e.g., the sixth bit indicates whether or not it itself asks for communication of the SPDIF signal, i.e., activation of the channel of the [Audio Return Channel]. This other one bit of the fifth byte is set to “1” when asking for activation, and is set to “0” when not asking for activation. 
     Also, another one bit of the fifth byte, e.g., the fifth bit indicates whether or not it itself asks for communication of the Ethernet signal, i.e., activation of the channel of the [Ethernet Channel]. This other one bit of the fifth byte is set to “1” when asking for activation, and is set to “0” when not asking for activation. Also, the remaining five bits of the fifth byte, e.g., the fourth bit through the zero&#39;th bit are set to reserved bits, and are all set to “0”. 
     As described above, in the case that a direct mode bit is provided to each message, for example, the following operation is executed. That is to say, at the time of exchange of the function information according to the &lt;Active Supported Channels&gt; message, confirmation is made whether or not supporting communication with the HPD signal as “L”, i.e., the direct mode. Subsequently, in the case that support for the direct mode has been confirmed, transmission/reception of the &lt;Exchange Supported Channels Info&gt; message is executed in the direct mode. 
     The source (Initiator) is allowed to transmit the CDC message in the direct mode between two CDC devices which support the direct mode. The source (Initiator) does not transmit the same CDC message to other CDC devices, and also the destination (Target) does not transfer the received CDC message to other CDC devices. 
     For example, let us consider a configuration example of an AV system  20  such as shown in  FIG. 18 . A CDC device  21  which is a source (Initiator) includes three ports  21   a  through  21   c . A CDC device  22  which is a destination (Target) includes four ports  22   a  through  22   d . The port  21   a  of the CDC device  21 , and the port  22   a  of the CDC device  22  which is the destination (Target) are connected. 
     In this case, in the event that the CDC device  21  which is the source (Initiator) transmits the CDC message to the CDC device  22  which is the destination (Target), this CDC device  22  outputs the CDC message to the port  21   a , but does not output the same CDC message to the other ports  21   b  and  21   c . Also, the CDC device  21  which is the source (Initiator) does not transfer the CDC message transmitted to the port  22   a  in the direct mode to the other ports  22   b  through  22   d.    
     As described above, the CDC device which supports the direct mode has a function for subjecting the CDC message to filtering. However, the method of filtering is an issue of processing within a device, and accordingly, there is no need to be defined as a transmission standard. 
     As described above, the direction mode is provided, whereby transmission/reception of the CDC message can be executed between two CDC devices alone, and accordingly, even if the HPD signal is “L”, and the physical address (Physical Address) of a source device side is unfixed, the validity of the CDC message is not deteriorated. 
     Example 2 
     With this Example 2, in addition to the &lt;Active Supported Channels&gt; message and the &lt;Exchange Supported Channels Info&gt; message, a &lt;Request HPD=H&gt; message for requesting that the HPD signal is set to “H” is added, a source device is allowed to read the physical address (Physical Address) of itself from a sink device, thereby realizing improvement of the validity of the CDC message. The &lt;Request HPD=H&gt; message has a data structure, for example, such as shown in the following. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 3 
               
               
                   
                   
               
             
            
               
                   
                 
                   &lt;Request HPD = H&gt; 
                 
                 no operands 
               
               
                   
                   
               
            
           
         
       
     
     A CDC device (source device) wherein the HPD signal is “L”, and the physical address (Physical Address) of itself is unfixed, broadcasts the above &lt;Request HPD=H&gt; message. The CDC device which has received the &lt;Request HPD=H&gt; message sequentially sets the HPD signal at each port to “H” at least for a predetermined period of time, e.g., just for five minutes. The CDC device which has broadcasted the &lt;Request HPD=H&gt; message reads out the E-EDID to obtain the physical address of itself during a period while the HPD signal of the port of the CDC device (sink device) connected to itself is “H”. 
     Thus, the CDC device (source device) wherein the HPD signal is “L”, and the physical address of itself is unfixed uses the &lt;Request HPD=H&gt; message, whereby the physical address of itself can be obtained and determined, and accordingly, the validity of the CDC message can be improved. 
     Example 3 
     With this Example 3 as well, in addition to the &lt;Active Supported Channels&gt; message and the &lt;Exchange Supported Channels Info&gt; message, a &lt;Request HPD=H&gt; message for requesting that the HPD signal is set to “H” is added, a source device is allowed to read the physical address (Physical Address) of itself from a sink device, thereby realizing improvement of the validity of the CDC message. 
     In the case of the above Example 2, each CDC device which has received the &lt;Request HPD=H&gt; message sequentially sets the HPD signal at each port to “H”. Therefore, the CDC device which has output the &lt;Request HPD=H&gt; message has to wait for the HPD signal of the port of the CDC device (sink device) connected to itself to become “H”. In this case, if the hierarchy of the CDC device connected to itself is known, and only the CDC devices of this hierarchy set the HPD signal of each port to “H”, obtaining of the physical address can be executed rapidly. 
     Therefore, data for specifying the hierarchy of the physical address to be asked for setting the HPD signal to “H” is added to the &lt;Request HPD=H&gt; message of this Example 3. Also, with this Example 3, a &lt;Report HPD=H&gt; message is added. This &lt;Report HPD=H&gt; message is a CDC message that the CDC device which has set the HPD signal to “H” broadcasts, and includes the physical address of this CDC device. The &lt;Request HPD=H&gt; message and the &lt;Report HPD=H&gt; message have a data structure, for example, such as the following. 
     
       
         
           
               
             
               
                 TABLE 4 
               
               
                   
               
             
            
               
                 &lt;Request HPD = H&gt; 
               
            
           
           
               
               
               
               
               
            
               
                   
                 [Requested Layer] 
                 4 
                 bits 
                 This fields indicate PA 
               
               
                   
                   
                   
                   
                 layer of the CDC device. 
               
               
                   
                 [A of PA (A.B.C.D)] 
                 1 
                 bit 
                 request to x.0.0.0 
               
               
                   
                 [B of PA (A.B.C.D)] 
                 1 
                 bit 
                 request to z.x.0.0 
               
               
                   
                 [C of PA (A.B.C.D)] 
                 1 
                 bit 
                 request to z.z.x.0 
               
               
                   
                 [D of PA (A.B.C.D)] 
                 1 
                 bit 
                 request to z.z.z.x 
               
            
           
           
               
            
               
                 &lt;Report HPD = H&gt; 
               
            
           
           
               
               
               
               
               
            
               
                   
                 [Physical Address] 
                 2 
                 bytes 
                 PA of HPD = H 
               
               
                   
                   
               
            
           
         
       
     
     The &lt;Request HPD=H&gt; message will be described. This &lt;Request HPD=H&gt; message includes data of four bits of the third bit through the zero&#39;th bit for specifying the hierarchy of the physical address. The third bit is set to “1”, and the other bits are set to “0”, thereby specifying the first hierarchy (most significant hierarchy) of the physical address. Also, the second bit is set to “1”, and the other bits are set to “0”, thereby specifying the second hierarchy, or the first and second hierarchies of the physical address. Also, the first bit is set to “1”, and the other bits are set to “0”, thereby specifying the third hierarchy, or the first through third hierarchies of the physical address. Also, the zero&#39;th bit is set to “1”, and the other bits are set to “0”, thereby specifying the fourth hierarchy, or the first through fourth hierarchies of the physical address. 
     Also, the &lt;Report HPD=H&gt; message will be described. This &lt;Report HPD=H&gt; message includes data of two bytes. The physical address of the CDC device of which the HPD signal has been set to “H”, i.e., the physical address (Physical Address) of the source (Initiator) is disposed in the two bytes thereof. 
     Example 4 
     This Example 4 is an example wherein instead of using the &lt;Request HPD=H&gt; message such as the above Example 2 and Example 3, the voltage of the power supply line is changed, thereby requesting for setting the HPD signal to “H”. Specifically, the CDC device (source device) connected to a predetermined port of the CDC device (sink device) of which the HPD signal is “L” temporarily resets the voltage of the power supply line to ground voltage such as shown in  FIG. 19( b ) , and then raises the power supply line to +5V. 
     In response to voltage change in this power supply line, the CDC device (sink device) sets the HPD signal at the predetermined port to “H” at least for a predetermined period of time, e.g., just for five minutes, such as shown in  FIG. 19( a ) . Thus, the CDC device (source device) reads out the E-EDID from the CDC device (sink device) while the predetermined port of the HPD signal is “H” to obtain the physical address of itself. 
     Thus, the CDC device (source device) wherein the HDP signal is “L”, and the physical address of itself is unfixed changes the voltage of the power supply line, whereby the physical address of itself can be obtained from the CDC device (sink device) and determined, and accordingly, the validity of the CDC message can be improved. 
     Note that, with the above description, an arrangement has been made wherein, for example, from the disk recorder  210  to the television receiver  250 , the function information is inserted and transmitted during the blanking period of a video signal, or the function information is transmitted via the CEC line  84  which is the control data line, whereby the television receiver  250  side can be allowed to recognize whether or not this disk recorder  210  is an eHDMI-compatible device. 
     However, an arrangement may be made wherein the voltage of the first line, e.g., the reserve line of the HDMI cable  350  is changed, whereby the function information, and further, compatible transmission format information can be transmitted. 
     First Example 
     The disk recorder  210  changes the voltage of the first line, e.g., the reserve line of the HDMI cable  350 , thereby notifying the television receiver  250  that it itself is an eHDMI-compatible device. 
     The television receiver  250  detects the voltage change in the reserve line, thereby obtaining the function information indicating that the disk recorder  210  is an eHDMI-compatible device. In this case, the CPU  271  of the television receiver  250  makes up a function information obtaining unit. 
     Also, the disk recorder  210  may automatically change the voltage of the reserve line at the time of the television receiver  250  being connected thereto via the HDMI cable  350 , or may change the voltage of the reserve line at timing requested from the television receiver  250  side. The disk recorder  210  determines whether or not there has been a request from the television receiver  250  side according to the voltage change of the second line, e.g., the HPD line of the HDMI cable  350 . In this case, the CPU  271  of the television receiver  250  makes up a function information requesting unit, and the CPU  221  of the disk recorder  210  makes up a voltage change detecting unit. 
     Also, the disk recorder  210  can also notify the television receiver  250  of the information of the transmission format (application) that it supports itself by changing the voltage of the reserve line in a pulse shape in addition to that it itself is an eHDMI-compatible device. Here, the transmission format information is information indicating whether or not supporting only the SPDIF signal, whether or not supporting only the Ethernet signal, whether or not supporting both of the SPDIF signal and the Ethernet signal, or the like. In this case, the CPU  271  of the television receiver  250  makes up a format information obtaining unit. 
     For example, let us define that a pulse count  1  is compatible with only the SPDIF signal, a pulse count  2  is compatible with only the Ethernet signal, and a pulse count  3  is compatible with both of the SPDIF signal and the Ethernet signal. 
     Also, for example, let us define that the pulse count  1  is compatible with eHDMI (unknown transmission format), the pulse count  2  is compatible with only the SPDIF signal, the pulse count  3  is compatible with only the Ethernet signal, and the pulse count  4  is compatible with both of the SPDIF signal and the Ethernet signal. 
     Also, for example, let us define that the pulse count  1  is compatible with eHDMI (unknown transmission format), the pulse count  2  is compatible with only the SPDIF signal, the pulse count  3  is compatible with only the Ethernet signal, the pulse count  4  is compatible with both of the SPDIF signal and the Ethernet signal, and the pulse count  5  is reserve. 
     Thus, in the case that, with the disk recorder  210  side, the voltage of the reserve line is changed in a pulse shape according to the compatible transmission format, the television receiver  250  side can obtain the information of the transmission format that the disk recorder  210  supports based on the pulse count. Note that it can be conceived that the compatible transmission format (application) is represented with the voltage level or pulse phase instead of the pulse count. 
       FIG. 20  illustrates a configuration example of the disk recorder  210  and the television receiver  250  in the case of changing the voltages of the reserve line and the HPD line, as described above. In  FIG. 20 , the portions corresponding to those in  FIG. 8  are denoted with the same reference numerals, and detailed description will be omitted. 
     With the disk recorder  210 , the pin  14  of the HDMI terminal  211  is grounded via a connection switch  418  made up of a transistor and the like. On/off of this connection switch  418  is controlled with a control signal SW 1  from the CPU  221  (see  FIG. 2 ). Thus, the television receiver  250  can be notified that the disk recorder  210  is an eHDMI-compatible device by changing the voltage of the reserve line, and also the change thereof is represented with a pulse shape, whereby the television receiver  250  can also be notified of compatible transmission format (application) information. In this case, the connection switch  418  and the CPU  221  make up a function information transmission unit and a format information transmission unit. 
     Also, with the television receiver  250 , the pin  19  of the HDMI terminal  251  is grounded via a connection switch  450  made up of a transistor and the like. On/off of this connection switch  450  is controlled with a control signal SW 2  from the CPU  271  (see  FIG. 3 ). Thus, the television receiver  250  can request the disk recorder  210  to notify information regarding whether or not this disk recorder  210  is an eHDMI-compatible device by changing the voltage of the HPD line. In this case, the connection switch  450  and the CPU  271  make up a function information requesting unit. With this television receiver  250 , the function information indicating that the disk recorder  210  is an eHDMI-compatible device, and further, compatible transmission format information, can be obtained from the voltage Vrsv of the pin  14  of the HDMI terminal  251 . 
       FIG. 21  illustrates a voltage control example of the HPD line on the television receiver (sink device)  250  side, and a voltage control example of the reserve line on the disk recorder (source device)  210  side corresponding thereto. In the case of this example, first, as shown in  FIG. 21( a ) , the connection switch  450  of the television receiver  250  is set to an on state from an off state just for a predetermined period of time, and the voltage of the HPD (eHDMMI−) line is changed from low to high. Thus, a request is executed from the television receiver  250  to the disk recorder  210  so as to notify the function information and the like. 
     On the other hand, after the voltage of the HPD line is restored to a high state, the connection switch  418  of the disk recorder  210  is set from an off state to an on state, the voltage of the reserve line is changed from high to low as shown in  FIG. 21( b ) , and the function information indicating that the disk recorder  210  is an eHDMI-compatible device is transmitted from the disk recorder  210  to the television receiver  250 . 
     Thereafter, for example, during 100 msec., the connection switch  418  of the disk recorder  210  is subjected to switching control, and the voltage of the reserve line is changed from low to high repeatedly according to the transmission format that the disk recorder  210  can support. Thus, the transmission format information that the disk recorder  210  can support is transmitted from the disk recorder  210  to the television receiver  250 . Finally, the connection switch  418  is returned to an off state. 
     As shown in  FIG. 21( b ) , the voltage of the reserve line has been changed, and accordingly, with the television receiver  250 , the voltage of the reserve line is detected, whereby function information can be obtained wherein, for example, the disk recorder  210  is an eHDMI-compatible device, and further, the pulse count is three, and accordingly, for example, the disk recorder  210  supports both of the SPDIF signal and the Ethernet signal. 
     As described above, after the function information indicating that the disk recorder  210  is an eHDMI-compatible device, the compatible transmission format information transmitted from the disk recorder  210  is confirmed at the television receiver  250 , and eHDMI transmission is started between the television receiver  250  and disk recorder  210 . 
     Second Example 
     With the above first example, the voltage of the first line, e.g., the reserve line of the HDMI cable  350  is changed, thereby transmitting function information indicating that the disk recorder  210  is an eHDMI-compatible device, and compatible transmission format information from the disk recorder  210  to the television receiver  250 . 
     With this second example, the voltage of the reserve line of the HDMI cable  350  is further changed, the information of a transmission format that the television receiver  250  can support is transmitted from the television receiver  250  to the disk recorder  210 . With this second example, detailed description regarding the portions corresponding to those in the first example will be omitted. 
     After obtaining function information indicating that the disk recorder  210  is an eHDMI-compatible device, and compatible transmission format information by detecting voltage change in the reserve line, the television receiver  250  changes the voltage of the reserve line in a pulse shape to notify the disk recorder  210  of the information of a transmission format that it itself supports. In this case, the CPU  271  of the television receiver  250  makes up a format information transmission unit. The disk recorder  210  detects voltage change in the reserve line, thereby obtaining the information of the transmission format that the television receiver  250  supports. In this case, the CPU  221  of the disk recorder  210  makes up a format information obtaining unit. 
       FIG. 22  illustrates a configuration example of the disk recorder  210  and the television receiver  250 , as described above, in the case that the function information and the compatible transmission format information is transmitted from the disk recorder  210  to the television receiver  250 , and also the compatible transmission format information is transmitted from the television receiver  250  to the disk recorder  210 . In  FIG. 22 , the portions corresponding to those in  FIG. 20  are denoted with the same reference numerals, and detailed description thereof will be omitted. 
     With the television receiver  250 , the pin  14  of the HDMI terminal  251  is grounded via a connection switch  451  made up of a transistor and the like. On/off of this connection switch  451  is controlled with a control signal SW 3  from the CPU  271 . Thus, the television receiver  250  can notify the disk recorder  210  of the information of a transmission format that it itself supports by changing the voltage of the reserve line in a pulse shape. In this case, the connection switch  451  and the CPU  271  make up a format information transmission unit. The other configurations of the television receiver  250  in  FIG. 22  are the same as those in the television receiver  250  in  FIG. 20 . 
     Note that the configuration of the disk recorder  210  in  FIG. 22  is the same as the configuration of the disk recorder  210  in  FIG. 20 . With this disk recorder  210 , the information of a transmission format that the television receiver  250  supports can be obtained from the voltage Vrsv of the pin  14  of the HDMI terminal  211 , as described above. In this case, the CPU  221  of the disk recorder  210  makes up a format information obtaining unit. 
       FIG. 23  illustrates a voltage control example of the HPD line on the television receiver (sink device)  250  side, and a voltage control example of the reserve line on the disk recorder (source device)  210  side and the television receiver (sink device)  250  side corresponding thereto. 
     In the case of this example, first, as shown in  FIG. 23( a ) , the connection switch  450  of the television receiver  250  is set to an on state from an off state just for a predetermined period of time, and the voltage of the HPD (eHDMMI−) line is changed from low to high. Thus, a request is executed from the television receiver  250  to the disk recorder  210  so as to notify the function information and the like. 
     On the other hand, after the voltage of the HPD line is restored to a high state, the connection switch  418  of the disk recorder  210  is set from an off state to an on state, the voltage of the reserve line is changed from high to low as shown in  FIG. 23( b ) , and the function information indicating that the disk recorder  210  is an eHDMI-compatible device is transmitted from the disk recorder  210  to the television receiver  250 . 
     Thereafter, for example, during 100 msec., the connection switch  418  of the disk recorder  210  is subjected to switching control, and the voltage of the reserve line is changed from low to high repeatedly according to the transmission format that the disk recorder  210  can support. Thus, the information of a transmission format that the disk recorder  210  can support is transmitted from the disk recorder  210  to the television receiver  250  (declaration of transmittable format for the source side). Finally, the connection switch  418  is returned to an off state. 
     Also, thereafter, during 100 msec, for example, the connection switch  451  of the television receiver  250  is subjected to switching control, and as shown in  FIG. 23( b ) , the voltage of the reserve line is changed from low to high repeatedly according to the transmission format that the television receiver  250  can support. Thus, the information of a transmission format that the television receiver  250  can support is transmitted from the television receiver  250  to the disk recorder  210  (declaration of a transmittable format on the sink side). Finally, the connection switch  451  is returned to an off state. 
     As described above, with the television receiver  250 , the function information indicating that the disk recorder  210  is an eHDMI-compatible device, and the compatible transmission format information transmitted from the disk recorder  210  is confirmed, and with the disk recorder  210 , the compatible transmission format information transmitted from the television receiver  250  is confirmed, and then eHDMI transmission is started between the television receiver  250  and the disk recorder  210 . 
     Now, description will be made regarding a case where the television receiver  250  includes multiple HDMI terminals (HDMI ports). The television receiver  250  shown in the above  FIG. 3  includes a single HDMI terminal.  FIG. 24  illustrates the television receiver  250  including multiple, e.g., three HDMI terminals. In this  FIG. 24 , the portions corresponding to those in  FIG. 3  are denoted with the same reference numerals, and detailed description thereof will be omitted. 
     This television receiver  250  includes HDMI terminals  251   a  through  251   c , an HDMI switcher  255 , and high-speed data line interfaces  253   a  through  253   c . The HDMI switcher  255  selectively connects the HDMI terminals  251   a  through  251   c  to the HDMI reception unit  252 . With the HDMI reception unit  252 , the data of video (image) and audio to be input via the HDMI cable is obtained at the HDMI terminal connected thereto via the HDMI switcher  255 , of the HDMI terminals  251   a  through  251   c.    
     The high-speed data line interfaces  253   a  through  253   c  are bidirectional communication path interfaces made up of predetermined lines (the reserve line and HPD line) of the HDMI cable to be connected to the above HDMI terminals  251   a  through  251   c . The high-speed data line interfaces  253   a  through  253   c  are inserted between the Ethernet interface  274  and the HDMI terminals  251   a  through  251   c . The high-speed data line interfaces  253   a  through  253   c  are configured in the same way as the high-speed data line interface  253  in  FIG. 3 . 
     The other units of the television receiver  250  in  FIG. 24  are configured in the same way as those of the television receiver  250  shown in  FIG. 3 , and execute the same operation. 
     As described above, the disk recorder  210  changes the voltage of the reserve line after receiving a transmission request (trigger) for the function information and the like from the television receiver  250  according to voltage change in the HPD line, and transmits the function information and the like to the television receiver  250 . 
     Therefore, the television receiver  250  can execute a transmission request for the function information and the like in series as to a device such as the disk recorder  210  or the like connected to each of the HDMI terminals via the HDMI cable at arbitrary timing for each HDMI terminal such as shown in  FIGS. 25( a ) through ( c ) . Thus, reduction in the number of pins of the microcomputer (CPU  271 ) is anticipated. 
     Note that, in  FIGS. 25( a ) through ( c ) , “DDC5V” denotes the voltage of the power supply line, “HPD” denotes the voltage of the HPD line, and “Rsv” denotes the voltage of the reserve line. Input  3  in  FIG. 25( c )  illustrates that the power supply source of a device has been turned on, or connection has been performed, halfway. 
     Also, “Source” denotes the function information indicating being an eHDMI-compatible device, and the compatible transmission format information to be transmitted from a source device (e.g., disk recorder  210 ) to a sink device (e.g., television receiver  250 ). Also, “Sink” denotes the compatible transmission format information to be transmitted from a sink device (e.g., television receiver  250 ) to a source device (e.g., disk recorder  210 ). 
     The flowchart in  FIG. 26  illustrates an example of a processing procedure at the time of the CPU  271  of the television receiver (sink device)  250  executing a detection operation as to predetermined HDMI input. 
     In step ST 1 , the CPU  271  starts the processing, and then proceeds to processing in step ST 2 . In this step ST 2 , the CPU  271  determines whether or not the voltage (DDC5V) of the power supply line is 5V. 
     When the voltage (DDC5V) of the power supply line is 5V, in step ST 3  the CPU  271  determines whether or not another HDMI input is currently performing a detection operation of the function information, compatible transmission format information, and the like. At the time of currently performing a detection operation of another input, in step ST 4  the CPU  271  determines whether or not detection of another input has ended. 
     At the time of detection of another input having ended, the CPU  271  proceeds to processing in step ST 5 . Note that when another input is not currently performing a detection operation, the CPU  271  immediately proceeds to the processing in step ST 5 . In this step ST 5 , the CPU  271  changes the voltage of the HPD line from low to high, and requests a source device on the partner side (disk recorder  210  or the like) of transmission of the function information and the like. 
     Next, in step ST 6 , the CPU  271  monitors the voltage of the reserve line to determine whether or not reply has been received from the source device, i.e., whether or not the function information and the like has been transmitted. When no reply has been received, in step ST 7  the CPU  271  determines whether or not 100 milliseconds have elapsed since a transmission request was performed in step ST 5 . At the time of 100 milliseconds having not elapsed, the CPU  271  returns to the processing in step ST 6 . On the other hand, at the time of 100 milliseconds having elapsed, in step ST 8  the CPU  271  determines that the source device on the partner side is an eHDMI-incompatible device. 
       FIG. 27  illustrates a voltage change example of the HPD line and the reserve line in the case of the CPU  271  determining that the source device on the partner side is an eHDMI-incompatible device. Note that  FIG. 27( a )  illustrates the voltage (DDC5V) of the power supply line,  FIG. 27( b )  illustrates the voltage of the HPD line, and  FIG. 27( c )  illustrates the voltage of the reserve line. 
     As shown in  FIG. 27( b ) , with the television receiver  250 , the voltage of the HPD line has been changed from low to high, and a transmission request for the function information and the like has been transmitted to the source device (disk recorder  210  or the like) on the partner side. However, as shown in  FIG. 27( c ) , thereafter, even if 100 milliseconds have elapsed, the voltage of the reserve line is still high, and there have been no reply from the source device. 
     Returning to the flowchart in  FIG. 26 , at the time of reply having been received in step ST 6 , in step ST 9  the CPU  271  recognizes that the source device on the partner side is an eHDMI-compatible device, and also detects the compatible transmission format of the source device on the partner side from voltage change in the reserve line. 
     Next, in step ST 10 , the CPU  271  changes the voltage of the reserve line in a pulse shape to transmit the information of a transmission format (application) that the television receiver  250  supports to the source device on the partner side. Subsequently, in step ST 11 , the CPU  271  starts transmission/reception of an eHDMI signal with the source device on the partner side. 
     With the processing of the flowchart in  FIG. 26 , at the time of reply from the source device having not been received even if 100 milliseconds have elapsed, the CPU  271  immediately determines that the source device is an eHDMI-incompatible device. However, as shown in  FIG. 28( b ) , at the time of reply from the source device having not been received even if 100 milliseconds have elapsed, the CPU  271  may execute retry processing wherein the voltage of the HPD line is changed from low to high several times (only once is shown in  FIG. 28( b ) ) to request transmission of the function information and the like, as to the partner source device (disk recorder  210  or the like). Thus, in the case that the source device has had difficulty in reply due to a busy state, a mistake of immediately determining that the source device is an eHDMI-incompatible device can be avoided. 
     Note that  FIG. 28( a )  illustrates the voltage (DDC5V) of the power supply line,  FIG. 28( b )  illustrates the voltage of the HPD line, and  FIG. 28( c )  illustrates the voltage of the reserve line.  FIGS. 28( a ) and ( c )  are the same as  FIGS. 27( a ) and ( c ) . 
     The flowchart in  FIG. 29  illustrates an example of the processing procedure of the CPU  221  of the disk recorder (source device)  210 . 
     In step ST 21 , the CPU  221  starts the processing, and then proceeds to processing in step ST 22 . In this step ST 22 , the CPU  221  determines whether or not the voltage of the reserve line is in a high state. When the voltage of the reserve line is not high, in step ST 23  the CPU  221  determines that the sink device on the partner side (television receiver  250  or the like) is an eHDMI-incompatible device. 
     When the voltage of the reserve line is high, the CPU  221  proceeds to processing in step ST 24 . In this step ST 24 , the CPU  221  determines whether or not the voltage of the HPD line has been changed from high, low, and high. At the time of such change, the CPU  221  determines that a transmission request for the function information and the like has been received from the sink device on the partner side. Subsequently, in step ST 25 , the CPU  221  changes the voltage of the reserve line to transmit the function information indicating that the source device is an eHDMI-compatible device, and the information of a compatible transmission format (application) to the sink device on the partner side. 
     Next, in step ST 26 , the CPU  221  monitors the voltage of the reserve line to determine whether or not there has been received reply from the sink device, i.e., whether or not the information of a transmission format that the sink device on the partner side can support has been transmitted. At the time of reply having not been received, in step ST 27 , the CPU  221  determines whether or not 100 milliseconds have elapsed since the function information of itself and the like was transmitted in step ST 25 . At the time of 100 milliseconds having not elapsed, the CPU  221  returns to the processing in step ST 26 . On the other hand, at the time of 100 milliseconds having elapsed, in step ST 28  the CPU  221  determines that the sink device on the partner side is an eHDMI-incompatible device, or incapable of transmission in a busy state. 
     At the time of reply having been received from the sink side in step ST 26 , in step ST 29  the CPU  221  detects the compatible transmission format of the sink device on the partner side from voltage change in the reserve line. Subsequently, in step ST 30 , the CPU  221  starts transmission/reception of an eHDMI signal with the sink device on the partner side. 
     Third Example 
     With the above first example and second example, the voltage of the second line, e.g., the HPD line of the HDMI cable  350  is changed, thereby transmitting a transmission request for the function information and the like from the television receiver (sink device)  250  to the disk recorder (source device)  210 . 
     With this third example, this transmission request is performed by changing the voltage of the first line, e.g., the reserve line of the HDMI cable  350 , in the same way as with the case of transmission of the function information, compatible transmission format information, and the like. Also, with this third example, a transmission request for the function information and the like can be output from both of the television receiver  250  and the disk recorder  210 . With this third example, detailed description will be omitted regarding the portions corresponding to those in the first example or second example. 
     The request side (sink device or source device) requests the reply side (source device or sink device) of transmission (start of condition transmission) of the function information indicating that the reply side is an eHDMI-compatible device by changing the voltage of the first line, e.g., the reserve line of the HDMI cable  350 . Here, the CPU of the request side makes up a function information requesting unit. 
     Next, the reply side monitors the voltage of the reserve line, and at the time of transmission (start of condition transmission) of the function information being requested from the request side, in the case that it itself is an eHDMI-compatible device, the reply side changes the voltage of the reserve line of the HDMI cable  350 , thereby transmitting the function information (reply of being capable of condition transmission) to the request side. The request side monitors the voltage of the reserve line to obtain the function information transmitted from the reply side. In this case, the reply side makes up a voltage change detecting unit and a function information transmission unit. Also, the request side makes up a function information obtaining unit. 
     Next, the request side changes the voltage of the reserve line in a pulse shape, thereby transmitting the transmission format information that the request side supports to the reply side. The reply side monitors the voltage of the reserve line to obtain the transmission format information that the request side supports. In this case, the request side makes up a format information transmission unit, and the reply side makes up a format information obtaining unit. 
     Next, the reply side changes the voltage of the reserve line in a pulse shape, thereby transmitting the transmission format information that the reply side supports to the request side. The request side monitors the voltage of the reserve line to obtain the transmission format information that the reply side supports. In this case, the reply side makes up a format information transmission unit, and the request side makes up a format information obtaining unit. 
       FIG. 30  illustrates a configuration example of the disk recorder  210  and the television receiver  250  in the case that the function information and the compatible transmission format information is transmitted from the disk recorder  210  to the television receiver  250 , and also the compatible transmission format information is transmitted from the television receiver  250  to the disk recorder  210 . In this  FIG. 30 , the portions corresponding to those in  FIG. 22  are denoted with the same reference numerals, and detailed description thereof will be omitted. 
     With the television receiver  250 , a transmission request for the function information is performed by changing the voltage of the first line, e.g., the reserve line of the HDMI cable  350 , thereby eliminating the necessity of the connection switch  450  of the television receiver  250 . The other configurations of the television receiver  250  in this  FIG. 30  are the same as those of the television receiver  250  in  FIG. 22 . Note that the configuration of the disk recorder  210  in  FIG. 30  is the same as the configuration of the disk recorder  210  in  FIG. 22 . 
       FIG. 31  illustrates a voltage control example of the reserve line.  FIG. 31( a )  illustrates the voltage of the HPD line,  FIG. 31( b )  illustrates the voltage of the reserve line. The voltage of the HPD line is still kept high. 
     In the case of this example, first, the connection switch on the request side (the connection switch  451  at the time of the television receiver  250  being the request side, and the connection switch  418  at the time of the disk recorder  210  being the request side) is set to an on state from an off state just for a predetermined period of time, and such as shown in  FIG. 31( b ) , the voltage of the reserve (eHDMMI−) line is changed form low to high. Thus, transmission of the function information (start of condition transmission) indicating that the reply side is an eHDMI-compatible device is requested from the request side to the reply side. 
     Thereafter, after elapse of the maximum two seconds, the connection switch on the reply side (the connection switch  418  at the time of the disk recorder  210  being the reply side, and the connection switch  451  at the time of the television receiver  250  being the reply side) is set to an on state from an off state just for a predetermined period of time, and as shown in  FIG. 31( b ) , the voltage of the reserve (eHDMMI+) line is changed form low to high. Thus, the function information (reply of being transmittable) indicating that the reply side is an eHDMI-compatible device is transmitted from the reply side to the request side. 
     Thereafter, for example, since 100 milliseconds elapsed, for example, during 100 milliseconds, the connection switch on the request side is subjected to switching control, and the voltage of the reserve line is changed from low to high repeatedly according to the transmission format that the request side can support. Thus, the information of a transmission format that the request side can support is transmitted from the request side to the reply side (declaration of a transmittable format on the request side). 
     Also, thereafter, for example, during 100 milliseconds, the connection switch on the reply side is subjected to switching control, and the voltage of the reserve line is changed from low to high repeatedly according to the transmission format that the reply side can support. Thus, the information of a transmission format that the reply side can support is transmitted from the reply side to the request side (declaration of a transmittable format on the reply side). 
     As described above, the function information indicating that the reply side is an eHDMI-compatible device, and the compatible transmission format information, transmitted from the reply side, is confirmed at the request side, and also the compatible transmission format information transmitted from the request side is confirmed at the reply side, following which eHDMI transmission is started between the request side and the reply side. 
     Now, description will be made regarding a case where a sink device includes multiple HDMI terminals (HDMI ports) (see the television receiver  250  in  FIG. 24 ). 
     As described above, after transmission of the function information from the reply side (reply of being capable of condition transmission), the request side changes the voltage of the reserve line to transmit the compatible transmission format information to the reply side. 
     Therefore, a sink device of multi-input (television receiver  250 ) can control the transmission timing of the function information (reply of being transmittable) even in the event that transmission of the function information (start of condition transmission) is requested from a source device at arbitrary timing for each HDMI terminal, and transmission/reception of the compatible transmission format information at each HDMI terminal can be executed in accordance with the processing situation of itself. 
     Note that, in  FIGS. 32( a ) through ( c ) , “DDC5V” denotes the voltage of the power supply line, “HPD” denotes the voltage of the HPD line, and “Rsv” denotes the voltage of the reserve line. Input  2  in  FIG. 32( b )  illustrates that the power supply source of a device has been turned on, or connection has been performed, halfway. 
     The flowchart in  FIG. 33  illustrates, in the case that a request is output from a sink device, an example of the processing procedure of the CPU (hereafter, referred to as “CPUsi”) of this sink device. 
     In step ST 41 , the CPUsi starts the processing, and thereafter, proceeds to processing in step ST 42 . In this step ST 42 , the CPUsi determines whether or not the voltage (DDC5V) of the power supply line is 5V. 
     When the voltage (DDC5V) of the power supply line is 5V, in step ST 43  the CPUsi determines whether or not another HDMI input is currently performing a detection operation of the function information, compatible transmission format information, and the like. At the time of currently performing a detection operation of another input, in step ST 44  the CPUsi determines whether or not detection of another input has ended. 
     At the time of detection of another input having ended, the CPUsi proceeds to processing in step ST 45 . Note that when another input is not currently performing a detection operation, the CPUsi immediately proceeds to the processing in step ST 45 . In this step ST 45 , the CPUsi changes the voltage of the reserve line from low to high, and requests a source device of transmission of the function information (start of condition transmission). 
     Next, in step ST 46 , the CPUsi monitors the voltage of the reserve line to determine whether or not reply has been received from the source device, i.e., whether or not the function information (reply of being transmittable) has been transmitted. When no reply has been received, in step ST 47  the CPUsi determines whether or not two seconds have elapsed since a transmission request was performed in step ST 45 . In the event of two seconds having not elapsed, the CPUsi returns to the processing in step ST 46 . On the other hand, at the time of two seconds having elapsed, in step ST 48  the CPUsi determines that the source device on the partner side is an eHDMI-incompatible device. 
       FIG. 34  illustrates a voltage change example of the reserve line in the case that determination is made that the source device on the partner side is an eHDMI-incompatible device. Note that  FIG. 25( a )  illustrates the voltage (DDC5V) of the power supply line,  FIG. 34( b )  illustrates the voltage of the HPD line, and  FIG. 34( c )  illustrates the voltage of the reserve line. 
     As shown in  FIG. 34( c ) , with the sink device, the voltage of the reserve line has been changed from low to high, and a transmission (start of condition transmission) request for the function information has been transmitted to the source device on the partner side. However, as shown in  FIG. 34( c ) , thereafter, even if two seconds have elapsed, the voltage of the reserve line is still high, and there have been no reply from the source device. 
     Returning to the flowchart in  FIG. 33 , at the time of reply having been received in step ST 46 , in step ST 49  the CPUsi changes the voltage of the reserve line to transmit the information of a transmission format (application) that the sink device supports to the source device on the partner side. 
     Next, in step ST 50 , the CPUsi monitors the voltage of the reserve line. Subsequently, the CPUsi detects the compatible transmission format of the source device on the partner side from voltage change in the reserve line. Subsequently, in step ST 51 , the CPUsi starts transmission of an eHDMI signal with the source device on the partner side. 
     With the processing of the flowchart in  FIG. 33 , at the time of reply from the source device having not been received even if two seconds have elapsed, the CPUsi immediately determines that the source device is an eHDMI-incompatible device. However, as shown in  FIG. 35( c ) , at the time of reply from the source device having not been received even if two seconds have elapsed, the CPUsi may execute retry processing wherein the voltage of the reserve line is changed from low to high several times (only once is shown in  FIG. 35( c ) ) to output a transmission request (condition transmission start request) of the function information to the source device on the partner side. Thus, in the case that the source device has had difficulty in reply due to a busy state, a mistake of immediately determining that the source device is an eHDMI-incompatible device can be avoided. 
     Note that  FIG. 35( a )  illustrates the voltage (DDC5V) of the power supply line,  FIG. 35( b )  illustrates the voltage of the HPD line, and  FIG. 35( c )  illustrates the voltage of the reserve line.  FIGS. 35( a ) and ( b )  are the same as  FIGS. 34( a ) and ( b ) . 
     The flowchart in  FIG. 36  illustrates an example of the processing procedure of the CPUsi of the sink device in the case that a request is output from the source device. 
     In step ST 61 , the CPUsi starts the processing, and then proceeds to processing in step ST 62 . In this step ST 62 , the CPUsi determines whether or not the voltage (DDC5V) of the power supply line is 5V. 
     When the voltage (DDC5V) of the power supply line is 5V, in step ST 63  the CPUsi monitors the voltage of the reserve line to detect change of low to high. Subsequently, the CPUsi determines that a request of transmission (start of condition transmission) of the function information from the source side, and proceeds to processing in step ST 64 . In this step ST 64 , the CPUsi determines whether or not another HDMI input is currently performing a detection operation of the function information, the compatible transmission format information, and the like. 
     At the time of currently performing a detection operation of another input, in step ST 65  the CPUsi determines whether or not two seconds has elapsed since change in voltage of low to high of the reserve line was detected in step ST 63 . At the time of two seconds having not elapsed, the CPUsi returns to the processing in step ST 64 . At the time of two seconds having elapsed, in step ST 66  the CPUsi gives up transmission of the function information (reply of being transmittable). Note that in the case of intending to execute transmission of the function information (reply of being transmittable), a request for transmission (start of condition transmission) of the function information is output from the sink side again. 
     When another input is not currently performing a detection operation in step ST 64 , the CPUsi proceeds to processing in step ST 67 . In this step ST 67 , the CPUsi changes the voltage of the reserve line from low to high to transmit the function information (reply of being transmittable) to the source device. Subsequently, in step ST 68 , the CPUsi monitors the voltage of the reserve line to detect the compatible transmission format of the source device on the partner side from change in voltage of the reserve line. 
     Next, in step ST 69 , the CPUsi changes the voltage of the reserve line in a pulse shape to transmit the information of the transmission format (application) that the sink device supports to the source device on the partner side. Subsequently, in step ST 70 , the CPUsi starts transmission/reception of an eHDMI signal with the source device on the partner side. 
     The flowchart in  FIG. 37  illustrates an example of the processing procedure of the CPUso of the source device in the case of outputting a request from the source device. 
     In step ST 81 , the CPUso starts the processing, and then proceeds to processing in step ST 82 . In this step ST 82 , the CPUso determines whether or not the voltage of the reserve line is in a high state. When the voltage of the reserve line is not high, in step ST 83  the CPUso determines that the sink device on the partner side is an eHDMI-incompatible device. 
     When the voltage of the reserve line is high, the CPUso proceeds to processing in step ST 84 . In this step ST 84 , the CPUso determines whether or not the voltage of the reserve line is still high. When the voltage of the reserve line is not still high, the CPUso proceeds to processing in step ST 85 . In this step ST 85 , the CPUso determines whether or not the voltage of the reserve line restores to high after a predetermined period of time. When not restoring to high, the CPUso determines that connection has been separated. On the other hand, when restoring to high, the CPUso determines that a request has occurred from the sink device, and proceeds to processing in step ST 104  of the later-described flowchart in  FIG. 38 . 
     When the voltage of the reserve line is still high in step ST 84 , the CPUso proceeds to processing in step ST 88 . In this step ST 88 , the CPUso changes the voltage of the reserve line from low to high to request transmission (start of condition transmission) of the function information. 
     Next, in step ST 89 , the CPUso monitors the voltage of the reserve line to determine whether or not reply has arrived from the sink device, i.e., whether or not the function information (reply of being transmittable) has been transmitted. At the time of reply having not been transmitted, in step ST 90  the CPUso determines whether or not two seconds have elapsed since transmission was requested in step ST 88 . At the time of two seconds having not elapsed, the CPUso returns to the processing in step ST 89 . On the other hand, at the time of two seconds having elapsed, in step ST 91 , the CPUso determines that transmission to the sink device on the partner side is impossible, and returns to the processing start in step ST 81 . 
     At the time of reply having arrived in step S 89 , in step ST 92  the CPUso changes the voltage of the reserve line in a pulse shape to transmit the information of the transmission format (application) that the source device supports to the sink device on the partner side. 
     Next, in step ST 93 , the CPUso monitors the voltage of the reserve line. Subsequently, the CPUso detects the compatible transmission format of the sink device on the partner side from change in voltage of the reserve line. Subsequently, in step ST 94 , the CPUso starts transmission/reception of an eHDMI signal with the sink device on the partner side. 
     With the processing of the flowchart in  FIG. 37 , at the time of reply from the sink device having not arrived even after elapse of two seconds, the CPUso immediately determines that transmission is impossible. However, at the time of reply from the sink device having not arrived even after elapse of two seconds, the CPUso may execute retry processing wherein the voltage of the reserve line is changed from low to high several times to output a transmission request (condition transmission start request) of the function information to the sink device on the partner side. Thus, in the case that the sink device has had difficulty in reply due to a busy state, a mistake of immediately determining that transmission is impossible can be avoided. 
     The flowchart in  FIG. 38  illustrates an example of the processing procedure of the CPUso of the source device in the case that a request is output from the sink device. 
     In step ST 101 , the CPUso starts the processing, and then proceeds to processing in step ST 102 . In this step ST 102 , the CPUso determines whether or not the voltage of the reserve line is in a high state. When the voltage of the reserve line is not high, in step ST 103  the CPUso determines that the sink device on the partner side is an eHDMI-incompatible device. 
     When the voltage of the reserve line is high, the CPUso proceeds to processing in step ST 104 . In this step ST 104 , the CPUso monitors the voltage of the reserve line to detect change of low to high. In this case, the CPUso detects a transmission request (condition transmission start request) of the function information from the sink device. 
     Next, in step ST 105 , the CPUso changes the voltage of the reserve line from low to high to transmit the function information (reply of being transmittable) to the sink device on the partner side. Subsequently, in step ST 106 , the CPUso monitors the voltage of the reserve line to detect the compatible transmission format of the sink device on the partner side from change in voltage of the reserve line. 
     Next, in step ST 107 , the CPUso changes the voltage of the reserve line in a pulse shape to transmit the information of the transmission format that the source device supports to the sink device on the partner side. Subsequently, in step ST 108 , the CPUso starts transmission/reception of an eHDMI signal with the sink device on the partner side. 
     As described above, with the AV system  200  shown in  FIG. 1 , the disk recorder  210  notifies the television receiver  250  of the information indicating that it itself is an eHDMI-compatible device, and the information of the transmission format (application) supported, when the television receiver  250  is connected thereto via the HDMI cable  350 , or when a transmission request is received from the television receiver  250 . 
     On the other hand, for example, as shown in  FIG. 39 , with an AV system  200 A wherein an eHDMI-incompatible disk recorder  210 A and the television receiver  250  are connected with the HDMI cable  350 , the above function information and transmission format information are not notified from the disk recorder  210 A to the television receiver  250 . 
     Therefore, the television receiver  250  can recognize whether or not the disk recorder  210  includes communication units (high-speed data interface, SPDIF reception circuit), i.e., whether or not the disk recorder  210  is an eHDMI-compatible device, and accordingly, an unnecessary signal can be prevented from being transmitted to the disk recorder  210 A which is an eHDMI-incompatible device via the communication path made up of the reserve line and the HPD line. 
     Also, the television receiver  250  can obtain from the disk recorder  210  which is an eHDMI-compatible device the information of the transmission format that this disk recorder  210  supports, and accordingly, compatibility with the SPDIF signal and the Ethernet signal of this disk recorder  210  can be readily known. 
     Note that, as described in the above embodiment, the function information is notified from the disk recorder  210  which is an eHDMI-compatible device to the television receiver  250 , which indicates that the disk recorder  210  is an eHDMI-compatible device. After recognizing that the disk recorder  210  is an eHDMI-compatible device, the television receiver  250  can execute transmission of the Ethernet signal or SPDIF signal via the communication path made up of the reserve line and the HPD line of the HDMI cable  350 . 
     However, there is a case where the disk recorder  210  intentionally determines to shut off communication with the communication units (high-speed data line interface  213 , SPDIF reception circuit  417 ). For example, this case is a case where the network terminal  225  is connected to a network, and communication using this network is prioritized, or a case where the power of the CPU  221  is shifted to another process within the device, or the like. For example, the CPU  221  determines whether or not communication by the communication units is thus shut off. Here, the CPU  221  makes up a shutoff determining unit. 
     When determining to shut off communication by the above communication units, the disk recorder  210  transmits communication information indicating shutoff of communication to the television receiver  250 . For example, the disk recorder  210  inserts the above communication information during the blanking period of a video signal to be transmitted to the television receiver  250  using the above TMDS channel in the same way as the above function information, thereby transmitting this communication information to the television receiver  250 . Here, the disk recorder  210  inserts the above communication information during the blanking period of a video signal, for example, using the AVI InfoFrame packet of HDMI, a GCP packet, or the like. 
     In the case that the disk recorder  210  inserts the communication information during the blanking period of a video signal to be transmitted to the television receiver  250  using the TMD channel as described above, thereby transmitting this communication information to the television receiver  250 , the television receiver  250  extracts the above communication information from the blanking period of the video signal received from the disk recorder  210 , thereby receiving this communication information. 
     Also, for example, the disk recorder  210  transmits the above communication information to the television receiver  250  via the CEC line  84  which is the control data line of the HDMI cable  350 . In this case, the television receiver  250  receives the communication information from the disk recorder  210  via the CEC line  84 . 
     The television receiver  250  can recognize that the disk recorder  210  is in a communication shutoff state by receiving the communication information such as described above. Thus, the television receiver  250  can prevent transmission of an unnecessary signal to the disk recorder  250  wherein communication using the communication units is shut off, via the above communication path. Note that, as described above, in the case that the communication information is transmitted from the disk recorder  210  to the television receiver  250 , the HDMI transmission unit  212  of the disk recorder  210  makes up an information transmission unit, and the HDMI reception unit  252  of the television receiver  250  makes up an information reception unit. 
     Note that, with the above description, the communication information is transmitted from the disk recorder  210  to the television receiver  250 , thereby enabling shutoff of communication by the communication units of the disk recorder  210  to be recognized at the television receiver  250  side. However, the disk recorder  210  can notify the television receiver  250  that the disk recorder  210  is in a communication shutoff state, by changing the voltage of the first line, e.g., the reserve line of the HDMI cable  350 . In this case, the disk recorder  210  sets the connection switch  418  (see  FIG. 20 ) from an off state to an on state to decrease the voltage of the reserve line. 
     The television receiver  250  can obtain the communication information indicating shutoff of communication by the communication units of the disk recorder  210  by detecting change in voltage of the reserve line. In this case, the CPU  271  of the television receiver  250  makes up an information obtaining unit. The television receiver  250  can recognize, as described above, that the disk recorder  210  shuts off communication by the communication units, by detecting the voltage of the reserve line to obtain the communication information. Thus, the television receiver  250  can prevent an unnecessary signal from being transmitted to the disk recorder  210  in a communication shutoff state via the above communication path. 
     Note that, with the above embodiment, description has been made assuming that the interface conforming to the HDMI standard is used as a transmission path for connecting each device, but the present invention may be applied to other similar transmission standards. Also, as an example, the disk recorder has been used as a source device, and the television receiver has been used as a sink device, but the present invention may be applied similarly to a case where other transmission device and reception device are used. Also, the above embodiment has illustrated a case where electronic devices are connected with the HDMI cable, but the present invention may be applied similarly to a case where electronic devices are connected wirelessly. 
     INDUSTRIAL APPLICABILITY 
     The present invention allows a signal to be transmitted suitably from a reception device to a transmission device, and may be applied to an AV system or the like wherein a source device and a sink device are connected via an HDMI cable.