Abstract:
A multimedia communication apparatus, suitable for a first multimedia apparatus, is adapted to transmit or receive multimedia data and is electrically connectable to a standard connector. The standard connector may be non-reversibly or reversibly connected to a plug of a standard cable, and includes a plurality of the pins. The pins include multiple differential signal pins serving as multiple multimedia channels, a power pin serving as a power line, a first polarity pin, a first data pin and a ground pin. The multimedia communication apparatus includes a control logic and a multimedia signal processor. The multimedia signal processor transmits or receives multimedia data to/from a second multimedia apparatus through the multimedia channels, and further power handshakes or exchanges information with the second multimedia apparatus. The information is for controlling a multiplexer to switch the multimedia channels.

Description:
[0001]    This application claims the benefit of U.S. provisional application Ser. No. 62/254,729, filed Nov. 13, 2015, the subject matter of which is incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    Field of the Invention 
         [0003]    The invention relates in general to a multimedia system and associated control method, and more particularly to a multimedia system and associated control method for transmitting multimedia data over a standard cable. 
         [0004]    Description of the Related Art 
         [0005]    High Definition Multimedia Interface (HDMI™) is a trademark of HDMI Licensing, LLC, and provides an all-digital image and sound transmission interface. HDMI is applicable to set-top boxes, DVD players, personal computers, television game consoles, integrated amplifiers, digital sound systems and televisions. HDMI is capable of simultaneously transmitting non-compressed audio and video signals, and significantly simplifies installation complications of system wires as the audio and video signals used the same cable. 
         [0006]    An HDMI transceiver adopts Transition-Minimized Differential Signaling (TMDS™) technologies, and encodes audio and video signals into data packets as TMDS data, which is then transmitted through a TMDS data channel as well as a TMDS clock channel. Each TMDS data channel supports a transmission speed up to 6 Gbps. An HDMI transceiver may also learn image transmission and reception capabilities of others through Display Data Channels (DDC) by using I 2 C signals to establish a correct multimedia link. Further, HDMI at the same time selectively offers a Consumer Electronics Control (CEC) function, which supports a function of operating multiple audiovisual devices using one single remote controller through a CEC channel that a signal line provides. HDMI further provides a function of Audio Return Channel (ARC), which allows the sound played by a television channel to return to an amplifier of a sound system. 
         [0007]    Universal Serial Bus (USB) is a serial port bus standard connecting a computer system to an external device, and is also an input/output interface standard that not only is extensively applied in information communication products such as personal computers and mobile devices but also expands functions to photographing equipments, digital televisions, set-top boxes, game consoles and other related fields. In the year 2014, the USB Implementers Forum (IF) published the USB3.1 connection interface design standard, which includes USB Type-C™ (commonly referred to as Type-C). One major feature of a Type-C connector compliant to the Type-C specification is that, the upper and lower sides of the Type-C connector appear identical, in a way that the Type-C connector may be plugged in both directions, i.e., reversibly and non-reversibly connected. 
         [0008]      FIG. 1  shows pin definitions of a Type-C receptacle defined by the Type-C specification. One Type-C receptacle includes 12 pins at each of its upper and lower sides. The pins A 1 , A 12 , B 1  and B 12  serve as ground lines GND. The pins A 4 , A 9 , B 4  and B 9  serve as bus power lines VBUS. According to the Type-C specification, the pins A 6  and B 6  are positive differential signal lines D+, and the pins A 7  and B 7  are negative differential signal lines D− to serve as a USB2.0 channel for transmitting USB2.0-compatible differential signals. The pins A 2  and A 3  provide a pair of SuperSpeed differential signal lines SSTX 1 + and SSTX 1 − serving as a SuperSpeed differential signal channel SSTX 1  for transmitting digital data at a speed as high as up to 10 Gbps. The pins A 11  and A 10  provide another pair of SuperSpeed differential signal lines SSRX 2 + and SSRX 2 − serving as a SuperSpeed differential signal channel SSRX 2  for receiving digital data at a speed as high as up to 10 Gbps. Similarly, the pins B 2  and B 3  provide a pair of SuperSpeed differential signal lines SSTX 2 + and SSTX 2 − serving as a SuperSpeed differential signal channel SSTX 2 ; the pins B 11  and B 10  provide another pair of SuperSpeed differential signal lines SSRX 1 + and SSRX 1 − serving as a SuperSpeed differential signal channel SSRX 1 . 
         [0009]    The pins A 8  and B 8  are respectively sideband use signal lines SBU 1  and SBU 2  for transmitting non-USB signals. For example, they may be used to transmit analog audio signals. 
         [0010]    The pins A 5  and B 5  respectively serve as configuration channels (CC) CC 1  and CC 2 . Through the pins A 5  and A 6 , or the configuration channels CC 1  and CC 2 , the polarity of a Type-C plug may be detected, i.e., whether the Type-C plug is non-reversibly or reversibly connected to a Type-C receptacle. Further, an upstream-facing port (UFP) and a downstream-facing port (DFP) connected at two ends of a Type-C cable may determine powering capabilities of the bus power line VBUS and the ground line GND according to a voltage dividing result generated by respective pull-up and pull-down resistors. The Type-C specification also provides a Power Delivery (PD) technology. In the standard mode of the Type-C specification, electronic devices connected at the two ends of a Type-C cable are capable of converting the USB PD protocol to Bi-phase Mark Coding (BMC) signals that may be transmitted to each other through the configuration channel CC 1  or CC 2 , hence completing the handshake of power transmission of the UFP and the DFP. 
         [0011]    Many electronic devices are equipped with both a USB socket and an HDMI socket. For example, the former is for connecting to an external memory, and the latter is for connecting to a display device. Different sockets need different cables, and more cables frequently lead to messier peripheral physical cables of these electronic devices. As the transmission speed of a Type-C cable is far greater than the transmission speed of an HDMI cable, transmitting HDMI signals using a Type-C cable may be a feasible solution. Therefore, there is a need for a solution that transmits HDMI signals using a Type-C cable while maintaining numerous technologies that the Type-C specification provides. 
       SUMMARY OF THE INVENTION 
       [0012]    A control method suitable for a first multimedia apparatus is provided according to an embodiment of the present invention. The first multimedia apparatus includes a standard connector that may be non-reversibly or reversible connected to a plug of a standard cable. The standard cable includes a power line and a ground line, a first configuration channel and a second configuration channel, a multimedia channel, and a serial data line and a serial clock line. The control method includes: detecting a connection polarity of the standard cable through the first configuration channel and the second configuration channel to determine whether the standard cable is non-reversibly or reversibly connected to the standard connector; switching the serial data line and the serial clock line according to the connection polarity to establish a display data channel; power handshaking with a second multimedia apparatus through the display data channel; transmitting power with the second multimedia apparatus through the power line according to a power handshake result; and transmitting multimedia data with the second multimedia apparatus through the multimedia channel. 
         [0013]    A multimedia communication apparatus is further provided according to an embodiment of the present invention. The multimedia communication apparatus is suitable for a first multimedia apparatus and is electrically connectable to a standard connector. The standard connector may be non-reversibly and reversibly connected to a plug of a standard cable, and includes a plurality of pins. The pins include a plurality of differential signal pins, a power pin, a first polarity pin, a first data pin and a ground pin. The differential signal pins serve as a plurality of multimedia channels. The power pin serves as a power line. The multimedia communication apparatus includes a control logic and a multimedia signal processor. The control logic checks a connection polarity of the standard cable through the first polarity pin to determine whether the standard cable is non-reversibly or reversibly connected to the standard connector. The multimedia signal processor, electrically connectable to the standard connector, transmits or receives multimedia data to/from a second multimedia apparatus through the multimedia channels. The multimedia signal processor further power handshakes or exchanges information with the second multimedia apparatus though the first data pin. The information is for controlling a multiplexer to switch the multimedia channels. 
         [0014]    The above and other aspects of the invention will become better understood with regard to the following detailed description of the preferred but non-limiting embodiments. The following description is made with reference to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1  shows pin definitions of a Type-C receptacle defined by the USB Type-C specification; 
           [0016]      FIG. 2  is a multimedia system according to an embodiment of the present invention; 
           [0017]      FIG. 3  to  FIG. 5  depict three multimedia systems, respectively representing three alternate modes, according to embodiments of the present invention; 
           [0018]      FIG. 6  shows a multimedia signal source device and a multimedia signal sink device respectively exemplifying a multimedia signal source device and a multimedia signal sink device in  FIG. 2 ; 
           [0019]      FIG. 7  shows a control method suitable for the multimedia signal source device and the multimedia signal sink device in  FIG. 6 ; 
           [0020]      FIG. 8  shows another control method suitable for the multimedia signal source device and the multimedia signal sink device in  FIG. 6 ; 
           [0021]      FIG. 9  shows a multimedia signal source device and a multimedia signal sink device respectively exemplifying the multimedia signal source device and the multimedia signal sink device in  FIG. 2 ; and 
           [0022]      FIG. 10  shows a control method suitable for the multimedia signal source device and the multimedia signal sink device in  FIG. 9 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0023]    Throughout the application, the same denotations represent elements having identical or similar structures, functions and principles, and may be anticipated by one person skilled in the art based on the teaching of the application. To keep the application simple, elements of the same denotations are not repeatedly described. 
         [0024]    According to an embodiment of the present invention, a multimedia signal source device and a multimedia signal sink device are connected to a cable through a Type-C connector. In an operation of a standard mode of the USB Type-C specification, the multimedia signal source device and the multimedia signal sink device transmit USB3.1-compliant signals through the Type-C connector and cable. The multimedia signal source device and the multimedia signal sink device are operable in an alternate mode to transmit HDMI signals by the Type-C cable. The multimedia signal source device includes an HDMI signal transmitter, and the multimedia signal sink device includes an HDMI signal receiver. Four pairs of SuperSpeed differential signal lines in the Type-C connector and cable respectively serve as three TMDS data channels and one TMDS clock channel to transmit TMDS data and clock. Each of the multimedia signal source device and the multimedia signal sink device similarly uses the configuration channels CC 1  and CC 2  in the Type-C connector and cable to determine the polarity of the Type-C plug connected thereto. Further, Hot Plug Detection (HPD) may also be implemented by the configuration channels CC 1  and CC 2  in the Type-C cable. In this embodiment, one of the multimedia signal source device and the multimedia signal sink device, through a display data channel (DDC) that is another data channel other than the configuration channels CC 1  and CC 2  in Type-C connector, may learn the connection polarity of the Type-C connector of the other of the multimedia signal source device and the multimedia signal sink device, so as to accordingly switch the TMDS channels and TMDS clock channel. Further, in this embodiment, through this DDC, the USB PD protocol may also be transmitted to accomplish USB PD handshaking. 
         [0025]    A special benefit is provided by using a data channel other than the configuration channels CC 1  and CC 2  as a display data channel. That is, neither of the HDMI signal transmitter and the HDMI signal receiver needs to be designed with a special input/output device for transmitting Bi-phase Mark Coding (BMC) signals, and the HDMI signal transmitter and the HDMI signal receiver can communication with each other through a normal input/output device. Under the Type-C specification, only BMC signals can be transmitted in the configuration channels CC 1  and CC 2 , and an input/output device with a special design is required because the signal swing of BMC signals is merely 1.125V. However, by adopting a data channel other than the configuration channels CC 1  and CC 2  as a display data channel, a signal having a full swing that is relatively slow in speed can be driven or received using a normal input/output device. In other words, in one embodiment of the present invention, input/output devices of the HDMI signal transmitter and signal receiver do not need to be especially designed to adapt to a Type-C connector, hence simplifying design complications. 
         [0026]      FIG. 2  shows a multimedia system according to an embodiment of the present invention. The multimedia system in  FIG. 2  includes a multimedia signal source device  102  and a multimedia signal sink device  104 , which are connected to each other through Type-C connectors  106  and  108  and a Type-C cable  110 . The multimedia signal source device  102  substantially serves as a downstream-facing port (DFP), includes an HDMI signal transmitter  112 , and provides HDMI signals to a corresponding signal channel according to the HDMI specification. The multimedia signal sink device  104  substantially serves as an upstream-facing port (UFP), includes an HDMI signal receiver  114 , and receives HDMI signals from a corresponding HDMI signal channel according to the HDMI specification. Different from the standard mode of the Type-C specification, the Type-C connectors  106  and  108  and the cable  110  in  FIG. 2  operate in an alternate mode. In another embodiment, the multimedia signal source device  102  and the multimedia signal sink device  104  may operate in the standard mode of the Type-C specification, and transmit USB signals through the Type-C connectors  106  and  108  and the cable  110 . 
         [0027]    As shown in  FIG. 2 , in the Type-C connectors  106  and  108  and the cable  110 , the four SuperSpeed differential signal channels SSTX 1 , SSR 1 , SST 2  and SSRX 2  in the original standard mode serve as three TMDS data channels Lane0, Lane1 and Lane2 and one TMDS clock channel CLK in the alternate mode. In other words, in the alternate mode, the four SuperSpeed differential signal channels SSTX 1 , SSRX 1 , SSTX 2  and SSRX 2 , instead of transmitting SuperSpeed differential signals, transmit the TMDS data and clock that the HDMI signal transmitter  112  generates based on the TMDS technology. In  FIG. 2 , the SuperSpeed differential signal channel SSTX 1  serves as the TMDS clock channel CLK, and the SuperSpeed differential signal channel SSRX 1  serves as the TMDS data channel Lane0 as an example of the embodiment, and such example is not to be construed as a limitation to the present invention. For example, in another embodiment, the SuperSpeed signal channel SSTX 1  serves as the TMDS data channel Lane0, and the SuperSpeed signal channel SSRX 1  serves as the TMDS clock channel CLK. That is to say, the correspondence of the TMDS data channels Lane0, Lane1 and Lane2 and the TMDS clock channel CLK, and the SuperSpeed signal lines SSTX 1 , SSRX 1 , SSTX 2  and SSRX 2  is not limited to that shown in  FIG. 2 , and may be determined by a system designer based on actual needs. 
         [0028]    As shown in  FIG. 2 , the multimedia signal source device  102  includes pull-down resistors  120  and  122 , which are respectively connected to the pins A 5  and B 5  on the Type-C connector  106 , i.e., the configuration channels CC 1  and CC 2 . The multimedia signal sink device  104  includes pull-up resistors  124  and  126 , which are respectively connected to the pins A 5  and B 5  on the Type-C connector  108 , i.e., the configuration channels CC 1  and CC 2 . The HMDI signal transmitter  112  may identify the connection polarity of the Type-C connector  106  through the pins A 5  and B 5  on the Type-C connector  106  to learn whether the Type-C cable  110  is non-reversibly or reversibly connected. The HDMI signal receiver  114  may identify the connection polarity of the Type-C connector  108  through the pins A 5  and B 5  on the Type-C connector  108 . 
         [0029]    In the Type-C specification, depending on the connection polarity of a Type-C plug plugged in a Type-C receptacle, one of the pins A 5  and B 5  on the Type-C connector  106  is shorted to one of the pins A 5  and B 5  on the Type-C connector  108  through the Type-C cable  110 , whereas the other of the pins A 5  and B 5  on the Type-C connector  106  remains open-circuit with the other of the pins A 5  and B 5  on the Type-C connector  108 . In other words, the Type-C cable  110  physically provides only one configuration channels. For example, in a connection polarity combination of a Type-C plug and a Type-C receptacle, the Type-C cable  110  causes the pin A 5  on the Type-C connector  106  to be electrically shorted to the pin A 5  on the Type-C, whereas the pin B 5  on the Type-C connector  106  and the pin B 5  on the Type-C connector  108  are kept open-circuit. The HDMI signal transmitter  112  may detect the potential on the pins A 5  and B 5  to learn the connection polarity of the Type-C connector  106  with a normal input/output device. For example, if the HDMI signal transmitter  112  discovers that the potential of the pin A 5  on the Type-C connector  106  starts rising and the potential of the pin B 5  on the Type-C connector  106  is kept at 0V, it means that the pin A 5  on the Type-C connector  106  is connected to the HDMI signal receiver  114  through the Type-C cable  110 , and the pin B 5  on the Type-C connector  106  is not. Thus, it may be determined that the connection polarity of the Type-C connector  106  is non-reversible. Similarly, the HDMI signal receiver  114  may also use a normal input/output device to detect the potential on the pins A 5  and B 5  on the Type-C connector  108  to learn the connection polarity of the Type-C connector  108 . For example, if the HDMI signal receiver  114  discovers that the potential of the pin B 5  on the Type-C connector  108  starts falling and the potential of the pin A 5  on the Type-C connector  108  is kept at a high voltage of 5V, it means that the pin B 5  on the on the Type-C connector  108  is connected to the HDMI signal transmitter  112  through the Type-C cable  110 , but the pin A 5  on the on the Type-C connector  108  is not. Thus, it may be determined that the connection polarity of the on the Type-C connector  108  is reversible. 
         [0030]    Similarly, when the multimedia signal source device  102  and the multimedia signal sink device  104  are initially electrically connected through the Type-C cable  110 , the potential of one of the configuration channels CC 1  and CC 2  is changed. Thus, the HDMI signal transmitter  112  may perform hot-plug detection (HPD) through the pins A 5  and B 5  on the Type-C connector  106 . Similarly, the HDMI signal receiver  114  may perform HPD through the pins A 5  and B 5  on the Type-C connector  108 . 
         [0031]    In the alternate mode in  FIG. 2 , the sideband use signal lines SBU 1  and SBU 2  are used as display data channels under the HDMI specification to transmit I 2 C signals to allow the HDMI signal receiver  114  and the HDMI signal transmitter  112  to learn the multimedia transmission and reception capabilities of each other. One of the sideband use signal lines SBU 1  and SBU 2  serves as a serial data line (SDA) and the other serves as a serial clock line (SCL), so that an instruction of the display data channel may be transmitted. Through the display data channel, the HDMI signal transmitter  112  may read the Extended Display Identification DATA (EDID) stored in the HDMI signal receiver  114  to determine types and formats of signals that the HDMI signal receiver  114  supports. For example, the HDMI signal transmitter  112  may learn the resolution that the HDMI signal receiver  114  is capable of outputting. 
         [0032]    As shown in  FIG. 2 , in the alternate mode, the two differential signal lines (one connected to the pins A 7  and B 7  of the Type-C connector, and the other connected to the pins A 6  and B 6  of the Type-C connector) originally for USB2.0 channels serve as ARC and CEC of the HMDI specification. 
         [0033]    The HDMI signal transmitter  112  and the HDMI signal receiver  114  may provide PD handshaking. In the alternate mode in  FIG. 2 , through the display data channel, i.e., the sideband use signal lines SBU 1  and SBU 2 , the HDMI signal transmitter  112  and the HDMI signal receiver  114  may handshake for the required power specification to be supplied using I 2 C signals. In  FIG. 2 , the HDMI signal transmitter  112  learns the power specification the HDMI signal receiver  114  requires, and then the multimedia signal source device  102  controls a DC-to-DC power converter  111  to power the multimedia signal sink device  104  through the bus power line VBUS. In another scenario, through the PD handshaking of the display data channel, the multimedia signal sink device  104  may also control a DC-to-DC power converter  113  to power the multimedia signal source device  102  through the bus power line VBUS. 
         [0034]    In  FIG. 2 , the PD handshaking required by the PD technology is completed though an instruction of the display data channel. The instruction of the display data channel may be completed by modifying associated firmware or software stored in the HDMI signal transmitter  112  and the HDMI signal receiver  114 . Thus, the HDMI signal transmitter  112  and the HDMI signal receiver  114  can be realized by normal input/output devices instead of requiring a specially designed BMC transceiver (TRX). Such feature provides tremendous convenience in the design of the HDMI signal transmitter  112  and the HDMI signal receiver  114 . 
         [0035]    For example, the HDMI signal receiver  114  may read and write (access) registers A, B, C and D therein, and the HDMI signal receiver  112  may access the registers A, B, C and D in the HDMI signal receiver  114  through the display data channel by using I 2 C signals. The register A stores information of power that the HDMI signal transmitter  112  is capable of supplying or needs, and such information is written by the HDMI signal transmitter  112 . The register B stores information of power that the HDMI signal receiver  114  is capable of supplying or needs, and such information is written by the HDMI signal receiver  114 . If one side of the HDMI signal transmitter  112  and the HDMI signal receiver  114  needs external power, the register A or B is read to confirm whether the other side is capable of providing the required power. If the other side is capable of providing the required power, the one side that needs the external power writes the register C of the HDMI signal receiver to raise a request of asking the other side for power. The one side that provides the power may read the powering request in the register C, and starts providing power if the power supply capability of the one side providing the power is greater than or equal to the powering request of the other side, or else does not output power or only outputs the power capable of providing if the powering capability of the one side providing the power is smaller than or equal to the powering request of the other side. Further, the one side providing the power writes the information to the register D of the HDMI signal receiver  114  to allow the other side receiving the power to learn the information by reading the register D. 
         [0036]    The HDMI signal transmitter  112  and the HDMI signal receiver  114  may transmit HDMI signals through the Type-C connector  110 , and perform connection polarity detection and HPD of the Type-C connector  110  through the configuration channels CC 1  and CC 2 . It is discovered from the above description that, both of the HDMI signal transmitter  112  and the HDMI signal receiver  114  can implement the PD technology without transmitting BMC signals. 
         [0037]      FIG. 2  is an example of an alternate mode according to an embodiment of the present invention, and is not to be construed as a limitation to the present invention.  FIG. 3  to  FIG. 5  further show three alternate modes according to embodiments of the present invention. Identical or similar parts to those in  FIG. 2  are omitted herein for brevity. Each of the alternate modes in  FIG. 3  to  FIG. 5  performs connection polarity detection and HPD through the configuration channels CC 1  and CC 2 , and also performs PD handshaking through the instruction of the display data channel. 
         [0038]    In the alternate mode in  FIG. 3 , the two differential signal lines originally used as USB2.0 channels serve as SDA and SCL the display data channel requires, respectively. The sideband use signal lines SBU 1  and SBU 2  are reserved for other purposes. 
         [0039]    In the alternate mode in  FIG. 4 , the two differential signal lines originally used as USB2.0 channels serve as SDA and SCL the display data channel requires, respectively. The sideband use signal lines SBU 1  and SBU 2  serve as ARC and CEC of the HDMI specification. 
         [0040]    In the alternate mode in  FIG. 5 , the USB2.0 channel in the Type-C cable is kept unchanged and is still used for transmitting differential signals compatible with USB2.0. The sideband use signal lines SBU 1  and SBU 2  serve as display data channels of the HDMI specification. 
         [0041]    In  FIG. 6 , a multimedia signal source device  102   a  and a multimedia signal sink device  104   a  are examples for illustrating the multimedia signal source device  102  and the multimedia signal sink device  104  in  FIG. 2 . 
         [0042]    The multimedia signal source device  102   a  includes a Type-C connector  106   a  and an HDMI signal transmitter  112   a . The HDMI signal transmitter  112   a  includes an HDMI signal source  160   a , a CC control logic and Vconn switch  162   a , and multiplexers (MUX)  164   a  and  166   a . The CC control logic and Vconn switch  162   a  identifies the connection polarity on the Type-C connector  106   a  through CC 1  and CC 2 , and controls the multiplexer  164   a  to correctly transmit display data channel signals that the HDMI signal source  160   a  provides to the corresponding SDA and SCL. The HDMI signal source  160   a  provides HDMI-compliant signals to the TMDS clock channel CLK, TMDS data channels Lane0, Lane1 and Lane2 and CEC. The multiplexer  166   a  is capable of switching the TMDS clock channel CLK and the TMDS data channel Lane1, and simultaneously switching the TMDS data channels Lane0 and Lane3. How the channels are switched are determined based on the actual mapping between the channels and pins. 
         [0043]    The multimedia signal sink device  104   a  includes a Type-C connector  108   a  and an HDMI signal receiver  114   a . The HDMI signal receiver  114   a  includes an HDMI signal processor  180   a , a CC control logic and a Vconn switch  182   a  for identifying the connection polarity on the Type-C connector  108   a , and control a multiplexer (MUX)  184   a  to correctly connect SDA and SCL to corresponding input ports of the HDMI signal processor  180   a . The HDMI signal processor  180   a  is directly connected to the TMDS clock channel CLK, the TMDS data channels Lane0, Lane1 and Lane2, ARC and CEC. It should be noted that, the multimedia signal sink device  104   a  does not include a multiplexer that switches the TMDS clock channel CLK and the TMDS data channel Lane1, or switch the TMDS data channels Lane0 and Lane3. 
         [0044]    As shown in  FIG. 6 , due to the connection polarities on the Type-C connectors  106   a  and  108   a , the mapping of the pins of the Type-C connector  106   a  and the Type-C connector  108   a  may be changed. For example, as shown in  FIG. 6 , under one connection polarity combination, the pin A 2  of the Type-C connector  106   a  is electrically shorted to the pin A 2  of the Type-C connector  108   a . Under another connection polarity combination, the pin A 2  of the Type-C connector  106   a  is electrically shorted to the pin B 2  of the Type-C connector  108   a.    
         [0045]      FIG. 7  shows a control method suitable for the multimedia signal source device  102   a  and the multimedia signal sink device  104   a  in  FIG. 6 . 
         [0046]    In step  302 , the multimedia signal sink device  104   a  performs HPD to check through the configuration channels CC 1  and CC 2  whether the multimedia signal source device  102   a  is electrically connected to the multimedia signal sink device  104   a  through the Type-C cable. 
         [0047]    In step  304  following step  302 , after it is confirmed that the multimedia signal source device  102   a  and the multimedia signal sink device  104   a  are electrically connected, the multimedia signal sink device  104   a  supplies a safe and limited power to the multimedia signal source device  102   a  through the bus power line VBUS and the ground line GND, to provide the multimedia signal source  102   a  with limited power for logic operations. In another scenario, the multimedia source apparatus  102   a  may supply a safe and limited power to the multimedia signal sink device  104   a  through the bus power line VBUS and the ground line GND, to provide the multimedia signal sink device  104   a  with limited power for logic operations. 
         [0048]    In step  306 , through the configuration channels CC 1  and CC 2 , the CC control logic and Vconn switch  162   a  identifies the connection polarity on the Type-C connector  106   a . Meanwhile, through the configuration channels CC 1  and CC 2 , the CC control logic and Vconn switch  182   a  identifies the connection polarity on the Type-C connector  108   a.    
         [0049]    In step  308 , the CC control logic and Vconn switch  162   a  controls the multiplexer  164   a  according to the detected connection polarity on the Type-C connector  106   a  to correctly transmit the display data channel signals that the HDMI signal source  160   a  provides to corresponding SDA and SCL. Similarly, the CC control logic and Vconn switch  182   a  controls the multiplexer  184   a  according to the detected connection polarity on the Type-C connector  108   a  to correctly connect SDA and SCL to the corresponding input ports of the HDMI signal processor  180   a . Thus, the display data channels between the HDMI signal processor  180   a  and the HDMI signal source  160   a  are correctly established. 
         [0050]    In step  308 , according to the connection polarity of the Type-C connector  106   a , the multiplexer  166   a  selectively temporarily allocates the TMDS clock channel CLK, and the TMDS data channels Lane0, Lane1 and Lane2 to some pins of the Type-C connector  106   a . Taking the TMDS clock channel CLK for example, if the Type-C connector  106   a  is non-reversibly connected, the multiplexer  166   a  allocates the TMDS clock channel CLK to the pins A 2  and A 3  of the Type-C connector  106   a ; if the Type-C connector  106   a  is reversibly connected, the multiplexer  166   a  allocates the TMDS clock channel CLK to the pins B 2  and B 3  of the Type-C connector  106   a.    
         [0051]    In step  310 , the HDMI signal source  160   a  and the HDMI signal processor  180   a  perform PD handshaking through the display data channel. 
         [0052]    According to the handshake result of step  310 , in step  312 , one of the HDMI signal processor  180   a  and the HDMI signal source  160   a  controls a DC-to-DC converter to provide a sufficiently large power to allow the other of the two to be operable. 
         [0053]    With the power being ready, in step  314 , the HDMI signal source  160   a  in the multimedia signal source device  102   a  starts providing TMDS clock signals to the TMDS clock channel CLK. 
         [0054]    In step  315 , the HDMI signal processor  180   a  checks whether the TMDS clock signal normally appears at the pins A 2  and A 3  of the Type-C connector  108   a , and records the checked result in a register of the HDMI signal processor  180   a . As shown in  FIG. 6 , in this alternate mode, the TMDS clock signal transmitted from the HDMI signal source  160   a , after passing through the multiplexer  166   a  and the Type-C cable that might be reversibly connected, may appear either at the pins B 2  and B 3  or the pins A 2  and A 3  of the Type-C connector  108   a . The pins A 2  and A 3  of the Type-C connector  108   a  are expectedly used as the TMDS clock channel CLK to allow the HDMI signal processor  180   a  with reception. Thus, at this point, the HDMI signal processor  180   a  may learn whether the TMDS clock channel CLK is connected by merely checking whether the TMDS clock channel normally appears in the TMDS clock channel CLK. 
         [0055]    In step  316 , the HDMI signal source  160   a  reads the checked result generated in step  315  and stored in the register to learn whether the HDMI signal processor  180   a  has correctly received the TMDS clock signal. 
         [0056]    Step  322  is performed when the HDMI signal processor  180   a  has received the TMDS clock signal through the TMDS clock channel CLK. In step  322 , the multimedia signal sink device  104   a  starts normally receiving the TMDS data and clock and plays the multimedia. 
         [0057]    When the TMDS clock signal does not appear at the pins A 2  and A 3  of the Type-C connector  108   a , the multimedia signal sink device  104  does not receive the TMDS clock signal. At this point, in an ideal situation, the TMDS clock is expectedly to appear at the pins B 2  and B 3  of the Type-C connector  108   a . Thus, step  320  is performed, in which the HDMI signal transmitter  112   a  causes the multiplexer  166   a  to swap the TMDS clock channel and the TMDS data channel Lane1, and to swap the TMDS data channels Lane0 and Lane2. As such, the TMDS clock signal should correctly appear at the pins A 2  and A 3  of the Type-C connector  108   a . The above channel swapping is an example, and the how the swapping is conducted is determined according to the actual pin definitions given by a designer. 
         [0058]    Step  323  follows step  320 . Similar to step  315 , in step  323 , it is checked whether the TMDS clock signal normally appears at the pins A 2  and A 3  of the Type-C connector  108   a , and the checked result is recorded in the register of the HDMI signal processor  180   a.    
         [0059]    Step  324  follows step  323 . Similar to step  316 , in step  324 , the HDMI signal source  160   a  reads the checked result generated in step  323  and stored in the register through the display data channel to learn whether the HDMI signal processor  180   a  has correctly received the HDMI clock signal. If so, step  322  is performed to start normally receiving the TMDS data and clock, and the multimedia is played. If not, it means that the multimedia signal source device  102   a  or the multimedia signal sink device  104   a  may contain certain issues and unexpected results have been generated. 
         [0060]    When the result in step  324  is negative, in step  326 , a physical or virtual plug event is triggered. For example, the HDMI signal processor  180   a  simultaneously pulls the pins A 5  and B 5  of the Type-C connector  108   a  to ground for a period of time and then releases the two. As such, the multimedia signal source device  102   a  deems that the Type-C cable has been virtually withdrawn and again plugged according to the detection result of the configuration channels CC 1  and CC 2 . Thus, the multimedia signal source device  102   a  may be reset to eliminate certain possible issues. 
         [0061]    Step  302  follows step  326  to re-start the entire control method. 
         [0062]    It is seen from  FIG. 6  and  FIG. 7  as well as the associated description that, when the multimedia signal source device  102   a  includes a multiplexer for switching the TMDS clock and the TMDS data channels Lane0, Lane1 and Lane2 whereas the multimedia signal sink device  104   a  does not, the TMDS clock channel CLK and the TMDS data channels Lane0, Lane1 and Lane2 may be correctly established to transmit HDMI signals. 
         [0063]    Step  316  in  FIG. 7  may check whether the TMDS clock signal normally appears to identify whether the TMDS clock channel and the TMDS data channels Lane0, Lane1 and Lane2 have been correctly established. It should be noted that, the above example is not to be construed as a limitation to the present invention. 
         [0064]    In an alternative embodiment, modifications may be made to  FIG. 7 , and the TMDS clock channel CLK and the TMDS data channels Lane0, Lane1 and Lane2 may still be correctly established. Step  314  is modified to providing TMDS data. Steps  315  and  323  are modified to that, the HDMI signal processor  180   a  checks and records whether the TMDS data correctly appears on one TMDS data channel to determine whether the TMDS clock channel CLK and the TMDS data channels Lane0, Lane1 and Lane2 have been correctly established. Steps  316  and  324  are modified to that, the HDMI signal source  160   a  learns through the display data channel whether the TMDS data normally appears on the TMDS data channel. 
         [0065]      FIG. 8  shows another control method suitable for the multimedia signal source device  102   a  and the multimedia signal sink device  104   a  in  FIG. 6 . According to the connection polarity, the TMDS clock channel CLK and the TMDS data channels Lane0, Lane1 and Lane2 are switched. Compared to  FIG. 7 ,  FIG. 8  does not include steps  315  and  316  but additionally includes steps  313  and  318 . In step  313 , the HDMI signal processor  180   a  records the checked result of the connection polarity of the Type-C connector  108   a  in step  306  in its register. In step  318 , the HDMI signal transmitter  112  reads the register in the HDMI signal processor  180   a  through the display data channel to learn the connection polarity of the Type-C connector  108   a , and compares the connection polarity of the Type-C connector  108   a  with the connection polarity of the Type-C connector  106   a . For example, when both of the Type-C connectors  108   a  and  106   a  are non-reversibly connected or reversibly connected, the comparison result of step  318  is affirmative, and so step  322  directly plays the multimedia. Otherwise, the comparison result of step  318  is negative, step  320  switches the TMD clock channel CLK, and the TMDS data channels Lane0, Lane1 and Lane2. As such, the TMDS clock channel CLK and the TMDS data channels Lane0, Lane1 and Lane2 may also be correctly established. 
         [0066]    Referring to  FIG. 9 , a multimedia signal source device  102   b  and a multimedia signal sink device  104   b  are examples of the multimedia signal source device  102   a  and a multimedia signal sink device  104   a  in  FIG. 2 . Parts in  FIG. 9  that are identical or similar to those in  FIG. 6  may be understood with reference to the description associated with  FIG. 6 , and the repeated details are omitted herein for brevity. One difference of  FIG. 9  from  FIG. 6  is that, between pins A 2 , A 3 , B 10  and B 11  of the Type-C connector  106   b  and an HDMI signal source  160   b , there is no multiplexer for switching the TMDS clock channel and the TMDS data channels Lane0, Lane1 and Lane  2 . Further, compared to  FIG. 6 , the HDMI signal receiver  114   a  in  FIG. 9  additionally includes a multiplexer  186   b  for switching the TMDS clock channel and the TMDS data channels Lane0, Lane1 and Lane  2 . 
         [0067]      FIG. 10  shows a control method suitable for the multimedia signal source device  102   b  and the multimedia signal sink device  104   b  in  FIG. 9 . Parts in  FIG. 10  that are similar or identical to  FIG. 7  may be learned with reference to the description associated with  FIG. 6 , and such repeated details are omitted herein for brevity. 
         [0068]    Steps  316  and  320  in  FIG. 7  are replaced by steps  319  and  321  in  FIG. 10 . In step  319 , the checked result recorded in the register in step  315  is looked up. When the TMDS clock signal is not received by the HDMI signal processor  180   b , it means that the TMDS clock signal is expected to appear at an incorrect receiving port of the HDMI signal processor  180   b . In an ideal situation, given that the multiplexer  186   b  switches the channels, the TMDS clock signal is expected to appear in the correct corresponding port in the HDMI signal processor  180   b . Thus, in step  321 , under a condition that the HDMI signal transmitter  112   b  is not notified, the HDMI signal receiver  114   b  swaps the TMDS clock channel CLK with the TMDS data channel Lane1, and swaps the TMDS data channels Lane0 and Lane2. As such, the TMDS clock signal of the Type-C connector  108   b  should be correctly transmitted to the HDMI signal processor  180   b.    
         [0069]    It is discovered from  FIGS. 8 and 9  and associated description that, when the multimedia signal sink device  104   b  includes a multiplexer for switching the TMDS clock channel CLK and the TMDS data channels Lane0, Lane1 and Lane2, but the multimedia signal source device  102   b  does not, the TMDS clock channel CLK and the TMDS data channels Lane0, Lane1 and Lane2 can be correctly established for transmitting HDMI signals. 
         [0070]    Similar to the foregoing teaching, in  FIG. 9 , the switching basis of the multiplexer  186   b  is not limited to whether the TMDS clock signal normally appears. For example, the switching basis of the multiplexer  186   b  may be based on whether the HDMI signal processor  180   b  normally receives TMDS data from the TMDS data channel, or based on the result of the connection polarity comparison performed by the HDMI signal processor  180   b.    
         [0071]    The embodiments of the present invention achieve at least one of the following advantages. 
         [0072]    1. Given that a Type-C receptacle is provided and a Type-C cable is used, the multimedia signal source device and the multimedia signal sink device are capable of transmitting HDMI signals without involving an HDMI socket. 
         [0073]    2. Without any design of a special input/output device for transmitting BMC signals, the multimedia signal source device and the multimedia signal sink device are capable of PD handshaking. 
         [0074]    3. USB2.0 signals may be transmitted between the multimedia signal source device and the multimedia signal sink device. 
         [0075]    While the invention has been described by way of example and in terms of the preferred embodiments, it is to be understood that the invention is not limited thereto. On the contrary, it is intended to cover various modifications and similar arrangements and procedures, and the scope of the appended claims therefore should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements and procedures.