Abstract:
A cable apparatus makes a selection between supply of an internal power to a predetermined interface device and that of an external power to the interface device in compliance with the interface standard applied to the predetermined interface device. The cable apparatus includes an internal power terminal connectable to an internal power source, a plurality of external power terminals connectable to an external power source, and a plurality of power lines connected to the internal power terminal and/or external power terminals. A power line selection controller is included to select, when an internal power is supplied from the internal power terminal, one of the power lines that allows a connection of the internal power from the internal power terminal to the plurality of external power terminals and when an external power is supplied from any one of the external power terminals, one of the power lines that allows to connect the external power from the external power terminal to the other external power terminals.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a cable apparatus for supplying power from an electronic apparatus to another electronic apparatus, and more particularly, to a cable apparatus for use in connecting a personal computer (will be referred to simply as “PC” hereinafter) to it associated peripheral devices. 
     2. Description of the Related Art 
     Generally, the computer system of a PC is configured such that the PC and its associated peripheral devices are connected to each other by a cable apparatus such as a power line via an interface for each of the peripheral devices. The computer system uses a display, keyboard, mouse, printer, modem, etc. as the peripheral devices. Recently, the video camera, electronic still camera and the like have been added to the above-mentioned PC-oriented peripheral devices. Namely, more and more kinds of peripheral devices are used with a PC. 
     The cable apparatus comprises a cable and a plug connected integrally to either end of the cable. It serves as a transmission path to convey a power and the like from a PC to each peripheral device. 
     For connection between the PC and each of its associated peripheral devices via the cable apparatus in a computer system, the PC is provided on its enclosure with many connecting terminals such as an analog RGB terminal, digital RGB terminal, etc. 
     Along with the increase in kind of the above-mentioned peripheral devices and improvement in PC performance in these years, cable apparatuses have been proposed for which plugs and receptacles have been standardized in shape as in the IEEE 1394 high-performance serial bus (will be referred to as “IEEE 1394” hereinafter) for connection of a variety of peripheral devices to a PC via a single interface. 
     The cable apparatus in conformity with the IEEE 1394 standard has been proposed for a compact design, lower cost, high versatility, etc. It comprises a cable having a power line, etc. and a small plug integrally secured to either end of the cable and having six terminals. 
     Namely, the cable apparatus conforming to the IEEE 1394 standard can connect power from a PC directly to its associated peripheral devices since it incorporates a power line. 
     Also, the interface according to the IEEE 1394 standard is characterized in that it can connect a plurality of peripheral devices to a PC and the cable can be connected to, and disconnected from, each of the peripheral devices while the latter is being energized and in operation, that is, in a hot status. 
     Next, a conventional cable apparatus will be described herebelow with reference to the accompanying drawings: 
     Referring now to FIG. 1, there is schematically illustrated in the fon-n of a block diagram a conventional cable apparatus adapted to supply both an internal power and an external power. Also, FIGS. 2A and 2B show schematic block diagrams of conventional cable apparatuses, one adapted to supply only an internal power (as in FIG. 2A) and the other adapted to supply only an external power (as in FIG.  2 B). 
     In FIG. 1, the conventional cable apparatus is generally indicated with a reference  120 . The cable apparatus  120  comprises a power supply unit  121 , Schottky diode  122 , fuses  123 ,  124  and  125 , and connectors  126 ,  127  and  128 . 
     In the cable apparatus  120 , the connectors,  126 ,  127  and  127  should desirably have a high impedance in relation to each other so that they will not influence each other. To supply and receive an external power between these connectors in case no internal power is supplied but the external power is supplied, however, the cable apparatus  120  is constructed as shown in FIG.  1 . To pass a current only when the internal power is supplied but no current when no internal power is supplied, the Schottky diode  122  is provided for each bus so that the power supply side works as an anode while each bus works as a cathode. 
     In the cable apparatus  120 , the power supply unit  121  supplies an internal power as will be described below: 
     As shown in FIG. 1, the power supply unit  121  supplies an internal power through the Schottky diode  122  to the connector  126  via the fuse  123 , connector  127  via the fuse  124 , and to the connector  128  via the fuse  125 , respectively. 
     Next, the power supply unit  121  which does not supply internal power, namely, in which an external power is supplied from the connectors, will be described below: 
     At least one (connector  126 ,  127 ,  128  for example) of the connectors  126  supplies the external power to the connector  127  via the fuses  123  and  124 , and to the connector  128  via the fuse&#39;s  123  and  125 , respectively. 
     The connectors  127  and  128  supply the external power to other connectors in the same manner as the connector  126 . The external power may be supplied to more than one of the connectors  126  to  128 . When no internal power is supplied, the connectors supply and receive an external power between them as in the above. 
     In FIG. 2A, the convention cable apparatus is generally indicated with a reference  130 . The cable apparatus  130  comprises a power supply unit  131 , fuse  132 , Schottky diodes  133 ,  134  and  135 , and connectors  136 ,  137  and  138 . 
     In the cable apparatus  130 , each of the connectors  136  to  138  has a higher impedance than the others. That is, the cable apparatus  130  is an ideal one in which an internal power can be supplied at a higher impedance at one of the connectors than the others. 
     In the cable apparatus  130 , the power supply unit  131  supplies an internal power as will be described below: 
     As shown in FIG. 2A, the power supply unit  131  supplies an internal power to the connector  136  via the fuse  132  and Schottky diode  133 , connector  137  via the fuse  132  and Schottky diode  134  and to the connector  138  via the fuse  132  and Schottky diode  135 , respectively. 
     However, when the power supply unit  131  supplies no internal power but an external power is supplied at the connectors  136 ,  137  and  138 , the power will not flow from the connectors  136 ,  137  and  138  to the fuse  132  because of the Schottky diodes  133 ,  134  and  135 , so that the connectors  136 ,  137  and  138  cannot supply and receive the external power between them. 
     Therefore, in the cable apparatus  130 , the connectors cannot supply any external power to one another. 
     Finally, a cable apparatus having no internal power source, namely, in which an external power is supplied from the connectors of the cable apparatus, will be described below: 
     In FIG. 2B, the conventional cable apparatus is generally indicated with a reference  140 . The cable apparatus  140  comprises fuses  141  and  142  and connectors  143 ,  144  and  145 . 
     In this conventional cable apparatus  140 , at least one (connector  143  for example) of the connectors  143  to  145  can supply an external power to the connector  144  via the fuse  141 , and to the connector  145  via the fuses  141  and  142 , as shown in FIG.  2 B. 
     The connectors  144  and  145  supply the external power to other connectors in the same manner as the connector  143 . The external power may be supplied to more than one of the connectors  143  to  145 . Thus in this cable apparatus  140 , no internal power can be supplied but the connectors  144  to  145  can supply and receive an external power between them. 
     Since in the cable apparatus  140 , the connectors  143  to  145  are connected to each other by means of fuses  141  and  142 , respectively, when an external power is supplied to the connectors  143 ,  144  and  145 , it can be supplied and received between the connectors and delivered from them to outside. 
     However, the conventional cable apparatuses do not strictly meet the requirements for power supply prescribed in the interface standard. In many of the conventional cable apparatuses, priority is given to reception of an external power. Thus, the conventional cable apparatuses are disadvantageous in that when an internal power is supplied, each bus will not have a high impedance in relation to each other. 
     Also, in the conventional cable apparatuses, the setting of power class conforming to the requirements in the IEEE 1394 standard are not automatically changed but the user has to change the setting using a switch on the keyboard or using GUI, a command or the like. Thus, failure to change a power class setting results in setting of a power class for supply of an external power or setting of quite a different power class setting from a required one. 
     OBJECT AND SUMMARY OF THE INVENTION 
     Accordingly the present invention has an object to overcome the above-mentioned drawbacks of the prior art by providing a cable apparatus adapted to make a selection between supply of an internal power to a predetermined interface device and that of an external power to the interface device in compliance with the interface standard applied to the predetermined interface device. 
     The above object can be attained by providing a cable apparatus comprising, according to the present invention: 
     an internal power terminal connectable to an internal power source; 
     a plurality of external power terminals connectable to an external power source; 
     a plurality of power lines connected to the internal power source and/or external power sources; and 
     a power line selection controlling means for selecting, when an internal power is supplied from the internal power terminal, one of the power line that allows to connect the internal power from the internal power terminal to the plurality of external power terminals, and when the external power is supplied from any one of the external power terminals, one of the power lines that allows to connect the external power from the external power terminal to the other external power terminals. 
     These objects and other objects, features and advantages of the present intention will become more apparent from the following detailed description of the preferred embodiments of the present invention when taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic block diagram of a conventional cable apparatus which is adapted to supply both an internal power and an external power; 
     FIGS. 2A and 2B shows schematic block diagrams of conventional cable apparatuses, one adapted to supply only an internal power and the other adapted to supply only an external power; 
     FIG. 3 is a schematic block diagram of a power supply node circuit according to the present invention; 
     FIG. 4 is a wiring diagram of a first embodiment of cable apparatus according to the present invention; 
     FIG. 5 is a wiring diagram of a power class controller used along with the first embodiment of cable apparatus according to the present invention; 
     FIG. 6 is a wiring diagram of a variant of the power class controller in FIG. 5; 
     FIG. 7 is a wiring diagram of another variant of the power class controller in FIG. 5; 
     FIG. 8 is a wiring diagram of a still another variant of the power class controller in FIG. 5; 
     FIG. 9 is a wiring diagram of a second embodiment of cable apparatus according to the present invention; and 
     FIG. 10 is a wiring diagram of a power class controller used along with the second embodiment of cable apparatus according to the present invention; 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention is applied to a power supply node circuit conforming to the IEEE 1394 standard. 
     Referring now to FIG. 3, there is schematically illustrated in the form of a block diagram an embodiment of power supply node circuit according to the present invention. The power supply node circuit is generally indicated with a reference  1 . 
     As shown in FIG. 3, the power supply node circuit comprises a power supply unit  2 , a cable apparatus  3  which is supplied with power from the cable apparatus-oriented power supply unit  2 , a power supply unit  4 , a physical interface circuit  5  (will be referred to as “PHY circuit” hereinafter) which is supplied with power from the power supply unit  4 , a grounding terminal  6  to connect the cable apparatus  3 , PHY circuit  5  to a ground potential, and a power class controller  7  which is supplied with a provider flag signal indicative of whether the cable apparatus  3  is supplied with the power from the cable apparatus-oriented cable apparatus  3  to the power supply unit  2  and also supplied with the power from the PHY circuit-oriented power supply unit  4 , to supply an output signal of a power class to the PHY circuit  5 . The power class controller  7  is also connected to the grounding terminal  6  and thus grounded by the latter. 
     FIG. 4 is a wiring diagram of a first embodiment of the cable apparatus  3  included in the embodiment of power supply node circuit I according to the present invention. 
     As will be seen from FIG. 4, the cable apparatus  3  comprises a power supply jack  11  connected to the cable apparatus-oriented power supply unit  2 , an electromagnetic interference (EMI) preventive circuit  12  connected to the power supply jack  11 , an semiconductor resistive element (will be referred to as “varistor” hereinafter)  13  connected to the EMI preventive circuit  12  to pass an overvoltage, and a positive-going resistive element  14  (will be referred to as “fuse” hereinafter) connected to the varistor  13 . 
     The cable apparatus  3  further comprises a resistor  15  connected to the fuse  14 , Schottky diodes  16 ,  17  and  18  connected at the anode thereof to the fuse  14 , a fuse  19 , a Schottky diode  20  connected at the cathode thereof to the resistor  15 , a relay circuit  21  having a terminal o connected to the resistor  15 , terminal p connected to the fuse  19 , terminal u connected to the cathode of the Schottky diode  18  and terminals q and t, and a fuse  22  connected to the terminals q and t of the relay circuit  21 . 
     Moreover, the cable apparatus  3  comprises a connector  23  connected to the cathode of the Schottky diode  16  and the fuse  22 , connector  24  connected to the cathode of the Schottky diode  17 , connector  25  connected to the cathode of the Schottky diode  18 , provider flag terminal  26  connected to a provider flag terminal  32  of the power class controller  7  shown in FIG. 5, and a grounding terminal  27  connected to the grounding terminal  6 . 
     Note that the voltage of the cable apparatus-oriented power supply unit  2  connected to the power supply jack  11  should be within the voltage range prescribed in the IEEE 1394 standard. To supply a necessary and sufficient current on which the relay circuit  21  not meeting the voltage range specified in the IEEE 1394 standard can operate, however, the resistor  15  is connected to the fuse  14  and the terminal o of the relay circuit  21 . 
     The Schottky diode  20  is provided to prevent a counter-electromotive force (CEMF) from being developed during operation of the relay circuit  21 . The CEMF will, if present, destroy or adversely affect all the circuits and devices. 
     Note that in the initial status where no internal power is supplied to the relay coil, the terminals p and u of the relay circuit  21  are electrically connected to the terminals q and t, respectively. 
     The cable apparatus  3  constructed as having been described in the foregoing functions as will be described below: 
     First, when the power supply jack  11  is plugged in the cable apparatus-oriented power supply unit  2 , a current flows to the relay coil via the power supply jack  11 , EMI preventive circuit  12  which suppresses an external electromagnetic field which will have an adverse influence on the circuits and parts of the apparatus, fuse  14  and the resistor  15 , whereby an internal power is supplied to the terminal o of the relay circuit  21  which shifts the switch from one position to another. 
     The varistor  13  connected to the EMI preventive circuit  12  which suppresses the influence of the external electromagnetic field on the apparatus circuits and parts and to the fuse  14  is provided to protect the apparatus circuits and parts from being destroyed due to a thunder or overvoltage, if applied. 
     When the power supply jack  11  is plugged in the cable apparatus-oriented power supply unit  2 , the latter supplies the internal power to the terminal p of the relay circuit  21  via the power supply jack  11 , EMI preventive circuit  12 , fuse  14 , Schottky diode  17  and the fuse  19 . 
     Also, when the power supply jack  11  is plugged in the cable apparatus-oriented power supply unit  2 , the latter supplies the internal power to the terminal u of the relay circuit  2   1  via the power supply jack  11 , EMI preventive circuit  12 , fuse  14  and the Schottky diode  18 . 
     Also, when the power supply jack  11  is plugged in the cable apparatus oriented power supply unit  2 , the latter supplies the internal power to the terminal a of the connector  23  via the power supply jack  11 , EMI preventive circuit  12 , fuse  14  and the Schottky diode  16 , to the terminal a of the connector  24  via the power supply jack  11 , EMI preventive circuit  12 , fuse  14  and the Schottky diode  17 , and to the terminal a of the connector  25  via the power supply jack  11 , EMI preventive circuit  12 , fuse  14  and the Schottky diode  18 , respectively. 
     In this case, the relay circuit  21  has the relay coil thereof energized with the supplied internal power to shift each of the switches from one position to another for the terminals p and u to be electrically connected to the terminals r and s, respectively. As the switches are thus shifted, the terminals a of the connectors  23 ,  24  and  25  of each bus, respectively, are not electrically connected to the power supply jack  11  via the relay circuit  21 . That is to say, the internal power from the power supply jack  11  is supplied to the terminals a of the connectors  23 ,  24  and  25  only via the Schottky diodes  16 ,  17  and  18 . 
     When the power supply jack  11  is not plugged in the cable apparatus-oriented power supply unit  2 , the latter will not supply the internal power to each terminal of the relay circuit  21  along the same route as in the above. 
     In this case, since no internal power is supplied to the relay coil of the relay circuit  21 , the switches are kept initially closed so that the terminals p and u are electrically connected to the terminals  9  and t, respectively. Since the switches remain in their initial status, the terminals a of the connectors  23 ,  24  and  25  of each bus are electrically connected to the terminals a of the connectors  23 ,  24  and  25 . 
     When the connector  23 , for example, is supplied with an external power, it delivers the external power at the terminal . thereof to the terminal a of the connector  24  via the fuse  22 , terminals q and p of the relay circuit  21  and the fuse  19 , and to the terminal a of the connector  25  via the fuse  22 , terminals t and u of the relay circuit  21 , respectively. 
     Thus, when supplied with an external power, each of the connectors  23 ,  24  and  25  can supply and receive the external power between them and further deliver it to outside. 
     Therefore, the connectors  23 ,  24  and  25  can supply and receive a power between predetermined interface devices. 
     FIG. 5 is a wiring diagram of the power class controller  7 , showing in detail the construction thereof. 
     As shown in FIG. 5, the power class controller  7  comprises a power terminal  31  connected to the PHY circuit-oriented power supply unit  4 , a provider flag terminal  32  connected to the provider flag terminal  26  shown in FIG. 4, a power class output terminal group  33  connected to the PHY circuit  5 , and a grounding terminal  34  connected to the grounding terminal  6 . 
     The power class controller  7  further comprises resistors  35 ,  36  and  37  connected to the provider flag terminal  32  and also connected in parallel to each other, a Zener diode  38  connected at the cathode thereof to the provider flag terminal  32 , and a capacitor  39  connected to the provider flag terminal  32  and also connected in parallel to the Zener diode  38  to kill any noise produced by the Zener diode  38  in operation. It should be noted that this circuit section of the power class controller  7  will be referred to hereinafter as a malfunction preventive circuit A which prevents the power class controller  7  from being caused to malfunction by a leakage current from the Schottky diodes  16 ,  17  and  18  when the external power is connected to the connectors, namely, to assure the positive operation of the power class controller  7 . 
     It should be noted that the Zener voltage of the Zener diode  38  should be higher than the voltage dropped across the resistors  35 ,  36  and  37  while being lower than the lowest voltage prescribed in the IEEE 1394 standard or a voltage of the cable apparatus-oriented power supply unit  2 . 
     In addition, the power class controller  7  comprises a transistor  40  connected at the base thereof to the anode of the Zener diode  38  and capacitor  39  and at the emitter thereof to the grounding terminal  34 , a resistor  41  connected to the power terminal  31  and collector of the transistor  40 , a transistor  42  connected at the base thereof to the resistor  41  and at the emitter thereof to the grounding terminal  34 , and a resistor  43  connected to the power terminal  31  and collector of the transistor  42 . It should be noted that this circuit section of the power class controller  7  will be referred to hereinafter as a theoretical value generation circuit B which generates a theoretical value for a power class. 
     Moreover, the power class controller  7  has jumpers  44 ,  45  and  46  connected to the power terminal  31 , a jumper  47  connected to the jumper  44  and resistor  41 , a jumper  48  connected to the jumper  45  and a jumper  50  also connected to the resistor  43 , a jumper  49  connected to the jumper  46  and a jumper  51  also connected to the resistor  43 , and wires  52 ,  53  and  54  connected to the power class output terminal group  33  and also connected in parallel to each other. 
     It should be noted that this circuit section of the power class controller  7  will be referred to hereinafter as a power class setting circuit C which sets a power class in compliance with the IEEE 1394 standard. 
     To use a power class setting in a fixed manner or to cope with changes of all power class settings, the power class setting circuit C is adapted such that is can be short-circuited to a logic power source and grounding terminal and provider flags H and L can be input to the power terminal  31 , power class output terminal  33  and grounding terminal  34 . 
     The cable apparatus functions depending upon a power class setting conforming to the IEEE 1394 standard as will be described below: 
     When a power class of “000” is set, the cable apparatus is supplied with neither internal power nor external power. 
     When a power class of “001” is set, the cable apparatus is supplied with an internal power of at least 15 W. 
     When a power class of “010” is set, the cable apparatus is supplied with an internal power of at least 30 W. 
     When a power class of “011” is set, the cable apparatus is supplied with an internal power of at least 45 W. 
     When a power class of “100” is set, the cable apparatus is supplied with no internal power but with an external power. In this case, the cable apparatus operates on the external power supplied over the bus and consumes a maximum of 1 W of the external power. 
     When a power class of “101” is set, the cable apparatus is supplied with no internal power but with an external power. In this case, the cable apparatus operates on the external power supplied over the bus and consumes a maximum of 1 W of the external power. To activate a link, an additional power of 2 W is required. 
     When a power class of “101” is set, the cable apparatus is supplied with no internal power but with an external power. In this case, the cable apparatus operates on the external power supplied over the bus and consumes a maximum of 1 W of the external power. To activate the link, an additional power of 5 W is required. 
     When a power class of “111” is set, the cable apparatus is supplied with no internal power but with an external power. In this case, the cable apparatus operates on the external power supplied over the bus and consumes a maximum of 1 W of the external power. To activate the link, an additional power of 9 W is required. 
     Four “installed” or “not-installed” states of the components including from the transistor  40  to the jumper  51  of the power class controller  7  will be described below. Note that the “installed” status of a component means that the component is in operation while the “not-installed” status of a component means that the component is not in operation. 
     When the cable apparatus-oriented power supply unit  2  can supply the terminals a of the connectors  23 ,  24  and  25  with an internal power of 15 W, the output of the power class output terminal group  33  is set for an output “001”. 
     When the transistor  40 , resistor  41 , transistor  42 , resistor  43 , and jumpers  48  and  51  are in the installed status while the jumpers  44  to  47  and jumpers  49  and  50  are in the not-installed status, the power class controller  7  will set the power class of “001” for the power class output terminal group  33  to supply a power class output which will allow the cable apparatus-oriented power supply unit  2  to supply an internal power of 15 W to the terminals a of the connectors  23 ,  24  and  25 . 
     The above operation will be described below with reference to FIG.  6 . The provider flag terminal  32  is supplied with an internal power from the cable apparatus-oriented power supply unit  2 . Thus, the voltage is applied to the cathode of the Zener diode  38  and the resistors  35 ,  36  and  37 . Since these resistors  35 ,  36  and  37  are adapted for a small drop of the voltage, this voltage is also applied to the anode of the Zener diode  38 . Since the transistor  40  is applied with the voltage because the anode of the Zener diode  38  is connected to the base of the transistor  40 , it is turned on. The collector of the transistor  40  will be at the same potential as the grounding terminal  34  since the transistor  40  is on. Therefore, the collector of the transistor  40  takes a potential which will be developed when the power class is set to “0”. 
     Since the transistor  40  is on, the base of the transistor  42  connected to the collector of the transistor  40  is at the same potential as the grounding terminal  34 . Thus, the transistor  42  will be off. The collector of the transistor  42  has the same potential as the power terminal  31  since the power voltage from the power terminal  31  passes through the resistor  43  because the transistor  42  is off Therefore, the collector of the transistor  42  takes a potential which will be developed when the power class is set to “1”. 
     Since the wire  52  of the power class output terminal group  33  is connected to the collector of the transistor  40 , it provides an output “0”. The wire  53  of the power class output terminal group  33  is connected to the grounding terminal  34  via the jumper  48  and thus provides an output “0”. Since the wire  54  of the power class output terminal group  33  is connected to the collector of the transistor  42  via the jumper  51 , it provides an output “1”. 
     Therefore, the power class output terminal group  33  will provide an output “001”, and thus the power class is known to be appropriately set. 
     In case the cable apparatus-oriented power supply unit  2  cannot supply an internal power of 15 W to the terminals a of the connectors  23 ,  24  and  25  depending upon whether the relevant components are in the “installed” or “not-installed” status, the power class output terminal group  33  is set for an output “100”. 
     The operation for this setting will be described with reference to FIG.  6 . When the cable apparatus-oriented power supply unit  2  can supply no internal power, the provider flag terminal  32  will not be applied with any voltage. Therefore, the cathode of the Zener diode  38  will have the same potential as the grounding terminal  34  since it is connected to the grounding terminal  34  via the resistors  35 ,  36  and  37 . The transistor  40  will be off because its base is at the same potential as the grounding terminal  34 . Therefore, the collector of the transistor  40  takes a potential which will be developed when the power class is set to “1”. 
     The base of the transistor  42  connected to the collector of the transistor  40  is at the same potential as the power terminal  31  since the power voltage from the power terminal  31  passes through the resistor  41  because the transistor  40  is off. The transistor  42  will be on since it is applied at its base with the power voltage from the power terminal  31 . Thus, the collector of the transistor  42  will be at the same potential as the grounding terminal  34 . Therefore, the collector of the transistor  42  takes a potential which will be developed when the power class is set to “0”. 
     Since the wire  52  of the power class output terminal group  33  is connected to the collector of the transistor  40 , it provides an output “1”. The wire  53  of the power class output terminal group  33  is connected to the grounding terminal  34  via the jumper  48  and thus provides an output “0”. Since the wire  54  of the power class output terminal group  33  is connected to the collector of the transistor  42  via the jumper  51 , it provides an output “0”. 
     Therefore, the power class output terminal group  33  provide an output “100”, and thus the power class is known to be appropriately set. 
     When the cable apparatus-oriented power supply unit  2  can supply an internal power of 30 W to the terminals a of the connectors  23 ,  24  and  25 , the power class output terminal group  33  is set for an output “010”. 
     When in the power class controller  7 , the transistor  40 , resistor  41 , transistor  42 , resistor  43 , and jumpers  49  and  50  are in the “installed” status while the jumpers  44  to  48  and jumper  51  are in the “not-installed” status, the power class output terminal group  33  is set for an output “010” which allows the cable apparatus-oriented power supply unit  2  to supply the internal power of 30 W to the terminals a of the connectors  23 ,  24  and  25 . 
     The above operation will be described below with reference to FIG.  7 . The provider flag terminal  32  is supplied with an internal power from the cable apparatus-oriented power supply unit  2 . Thus, the voltage is applied to the cathode of the Zener diode  38  and the resistors  35 ,  36  and  37 . Since these resistors  35 ,  36  and  37  are adapted for a small drop of the voltage, this voltage is also applied to the anode of the Zener diode  38 . Since the transistor  40  is applied with the voltage because the anode of the Zener diode  38  is connected to the base of the transistor  40 , it is turned on. The collector of the transistor  40  will be at the same potential as the grounding terminal  34  since the transistor  40  is on. Therefore, the collector of the transistor  40  takes a potential which will be developed when the power class is set to “0”. 
     Since the transistor  40  is on, the base of the transistor  42  connected to the collector of the transistor  40  is at the same potential as the grounding terminal  34 . Thus, the transistor  42  will be off The collector of the transistor  42  has the same potential as the power terminal  31  since the power voltage from the power terminal  31  passes through the resistor  43  because the transistor  42  is off. Therefore, the collector of the transistor  42  takes a potential which will be developed when the power class is set to “1”. 
     Since the wire  52  of the power class output terminal group  33  is connected to the collector of the transistor  40 , it provides an output “0”. The wire  53  of the power class output terminal group  33  is connected to the collector of the transistor  42  via the jumper  50  and thus provides an output “1”. Since the wire  54  of the power class output terminal group  33  is connected to the grounding terminal  34  via the jumper  49 , it provides an output “0”. 
     Therefore, the power class output terminal group  33  will provide an output “010”, and thus the power class is known to be appropriately set. 
     The power class controller  7  comprises resistors  35 ,  36  and  37  connected to the provider flag terminal  32  and also connected in parallel to each other, the Zener diode  38  connected at the cathode thereof to the provider flag terminal  32 , and the capacitor  39  connected to the provider flag terminal  32  and also connected in parallel to the Zener diode  38  to kill any noise developed by the Zener diode  38  in operation. It should be reminded that this circuit section of the power class controller  7  will be referred to hereinafter as a malfunction preventive circuit A which prevents the power class controller  7  from being caused to malfunction by a leakage current from the Schottky diodes  16 ,  17  and  18  when the external power is connected to the connectors, namely, to assure the positive operation of the power class controller  7 . 
     It should be noted that the Zener voltage of the Zener diode  38  should be higher than the voltage dropped across the resistors  35 ,  36  and  37  while being lower than the lowest voltage prescribed in the IEEE 1394 standard or a voltage of the cable apparatus-oriented power supply unit  2 . 
     The power class controller  7  comprises the transistor  40  connected at the base thereof to the anode of the Zener diode  38  and capacitor  39 , at the collector thereof to the resistor  41  and at the emitter thereof to the grounding terminal  34 , the resistor  41  being connected to the power terminal  31 , and the transistor  42  connected at the base thereof to the resistor  41 , at the collector thereof to the resistor  43  and at the emitter thereof to the grounding terminal  34 , the resistor  43  being also connected to the power terminal  31 . It should be noted that this circuit section of the power class controller  7  will be referred to hereinafter as a theoretical value generation circuit B which generates a theoretical value for a power class. 
     The power class controller  7  has the jumpers  44 ,  45  and  46  connected to the power terminal  31 , a jumper  47  connected to the jumper  44  and resistor  41 , a jumper  48  connected to the jumper  45  and a jumper  50  connected to the resistor  43 , a jumper  49  connected to the jumper  46  and a jumper  51  connected to the resistor  43 , and wires  52 ,  53  and  54  connected to the power class output terminal group  33  and also connected in parallel to each other. 
     In case the cable apparatus-oriented power supply unit  2  cannot supply an internal power of 30 W to the terminals a of the connectors  23 ,  24  and  25  depending upon whether the relevant components are in the “installed” or “not-installed” status, the power class output terminal group  33  is set for an output “100”. 
     The operation for this setting will be described with reference to FIG.  7 . When the cable apparatus-oriented power supply unit  2  can supply no internal power, the provider flag terminal  32  will not be applied with any voltage. Therefore, the cathode of the Zener diode  38  will have the same potential as the grounding terminal  34  since it is connected to the grounding terminal  34  via the resistors  35 ,  36  and  37 . The transistor  40  will be off because its base is at the same potential as the grounding terminal  34 . Therefore, the collector of the transistor  40  takes a potential which will be developed when the power class is set to “1”. 
     The base of the transistor  42  connected to the collector of the transistor  40  is at the same potential as the power terminal  31  since the power voltage from the power terminal  31  passes through the resistor  41  because the transistor  40  is off. The transistor  42  will be on since it is applied at its base with the power voltage from the power terminal  31 . Thus, the collector of the transistor  42  will be at the same potential as the grounding terminal  34 . Therefore, the collector of the transistor  42  takes a potential which will be developed when the power class is set to “0”. 
     Since the wire  52  of the power class output terminal group  33  is connected to the collector of the transistor  40 , it provides an output “1”. The wire  53  of the power class output terminal group  33  connected to the collector of the transistor  42  via the jumper  50  provides an output “0”. Since the wire  54  of the power class output terminal group  33  is connected to the grounding terminal  34  via the jumper  49 , it provides an output “0”. 
     Therefore, the power class output terminal group  33  provide an output “100”, and thus the power class is known to be appropriately set. 
     When the cable apparatus-oriented power supply unit  2  can supply an internal power of 45 W to the terminals a of the connectors  23 ,  24  and  25 , the power class output terminal group  33  is set for an output “011”. 
     When in the power class controller  7 , the transistor  40 , resistor  41 , transistor  42 , resistor  43 , and jumpers  50  and  51  are in the “installed” status while the jumpers  44  to  49  are in the “not-installed” status, the power class output terminal group  33  is set for an output “011” which allows the cable apparatus-oriented power supply unit  2  to supply the internal power of 45 W to the terminals a of the connectors  23 ,  24  and  25 . 
     The above operation will be described below with reference to FIG.  8 . The provider flag terminal  32  is supplied with an internal power from the cable apparatus-oriented power supply unit  2 . Thus, the voltage is applied to the cathode of the Zener diode  38  and the resistors  35 ,  36  and  37 . Since these resistors  35 ,  36  and  37  are adapted for a small drop of the voltage, this voltage is also applied to the anode of the Zener diode  38 . Since the transistor  40  is applied with the voltage because the anode of the Zener diode  38  is connected to the base of the transistor  40 , it is turned on. The collector of the transistor  40  will be at the same potential as the grounding terminal  34  since the transistor  40  is on. Therefore, the collector of the transistor  40  takes a potential which will be developed when the power class is set to “0”. 
     Since the transistor  40  is on, the base of the transistor  42  connected to the collector of the transistor  40  is at the same potential as the grounding terminal  34 . Thus, the transistor  42  will be off. The collector of the transistor  42  has the same potential as the power terminal  31  since the power voltage from the power terminal  31  passes through the resistor  43  because the transistor  42  is off. Therefore, the collector of the transistor  42  takes a potential which will be developed when the power class is set to “1”. 
     Since the wire  52  of the power class output terminal group  33  is connected to the collector of the transistor  40 , it provides an output “0”. The wire  53  of the power class output terminal group  33  connected to the collector of the transistor  42  via the jumper  50  provides an output “1”. Since the wire  54  of the power class output terminal group  33  is connected to the collector of the transistor  42  via the jumper  51 , it provides an output “1”. 
     Therefore, the power class output terminal group  33  will provide an output “011”, and thus the power class is known to be appropriately set. 
     In case the cable apparatus-oriented power supply unit  2  cannot supply an internal power of 45 W to the terminals a of the connectors  23 ,  24  and  25  depending upon whether the relevant components are in the “installed” or “not-installed” status, the power class output terminal group  33  is set for an output “100”. 
     The operation for this setting will be described with reference to FIG.  8 . When the cable apparatus-oriented power supply unit  2  can supply no internal power, the provider flag terminal  32  will not be applied with any voltage. Therefore, the cathode of the Zener diode  38  will have the same potential as the grounding terminal  34  since it is connected to the grounding terminal  34  via the resistors  35 ,  36  and  37 . The transistor  40  will be off because its base is at the same potential as the grounding terminal  34 . Therefore, the collector of the transistor  40  takes a potential which will be developed when the power class is set to “1”. 
     The base of the transistor  42  connected to the collector of the transistor  40  is at the same potential as the power terminal  31  since the power voltage from the power terminal  31  passes through the resistor  41  because the transistor  40  is off. The transistor  42  will be on since it is applied at its base with the power voltage from the power terminal  31 . Thus, the collector of the transistor  42  will be at the same potential as the grounding terminal  34 . Therefore, the collector of the transistor  42  takes a potential which will be developed when the power class is set to “0”. 
     Since the wire  52  of the power class output terminal group  33  is connected to the collector of the transistor  40 , it provides an output “1”. The wire  53  of the power class output terminal group  33  connected to the collector of the transistor  42  via the jumper  50  provides an output “0”. Since the wire  54  of the power class output terminal group  33  is connected to the collector of the transistor  42  via the jumper  51 , it provides an output “0”. 
     Therefore, the power class output terminal group  33  provide an output “100”, and thus the power class is known to be appropriately set. 
     FIG. 9 is a wiring diagram of the second embodiment of cable apparatus included in the power supply anode circuit  1  according to the present invention. The cable apparatus is generally indicated with a reference  60 . 
     Note that the cable apparatus  60  stands for the cable apparatus  3  having been described in the foregoing with reference to FIG.  3 . 
     As shown in FIG. 9, the cable apparatus  60  comprises a power supply jack  61  connected to the cable apparatus-oriented power supply unit  2 , and a Schottky diode  62  connected at the anode thereof to the power supply jack  61 . 
     The cable apparatus  60  further comprises a transistor  63  connected at the base thereof to an FET controller  91 , at the collector thereof to a resistor  66  and at the emitter thereof to a grounding terminal  92 , a Schottky diode  64  connected at the anode thereof to the cathode of the Schottky diode  62 , a Pch-FET  65  connected at the drain thereof to the cathode of the Schottky diode  62 and also connected in parallel to the Schottky diode  64 , a resistor  66 , a resistor  67  connected to the resistor  66 , cathode of the Schottky diode  64  and source and gate of the Pch-FET  65 , a Zener diode  68  connected at the cathode thereof to the cathode of the Schottky diode  64  and source of the Pch-FET  65  and at the anode thereof to the gate of the Pch-FET  65 , and a capacitor  69  connected to the cathode of the Schottky diode  64  and source and gate of the Pch-FET  65 . Note that the resistor  67 , Zener diode  68  and capacitor  69  are connected in parallel to each other. 
     Furthermore, the cable apparatus  60  comprises a transistor  70  connected at the base thereof to the FET controller  91 , at the collector thereof to a resistor  73  and at the emitter thereof to a grounding terminal  92 , a Schottky diode  71  connected at the anode thereof to the cathode of the Schottky diode  62 , a Pch-FET  72  connected at the drain thereof to the cathode of the Schottky diode  62  and in parallel to the Schottky diode  71 , a resistor  74  connected to the resistor  73 , cathode of the Schottky diode  71  and to the source and gate of the Pch-FET  72 , a Schottky diode  75  connected at the cathode thereof to the cathode of the Schottky diode  71  and source and gate of the Pch-FET  72 , and further at the anode thereof to the gate of the Pch-FET  72 , and a capacitor  76  connected to the cathode of the Schottky diode  71  and source and gate of the Pch-FET  72 . Note that the resistor  74 , Zener diode  75  and capacitor  76  are connected in parallel to each other. 
     In addition, the cable apparatus  60  comprises a transistor  77  connected at the base thereof to the FET controller  91 , at the collector thereof to a resistor  80  and at the emitter thereof to a grounding terminal  92 , a Schottky diode  78  connected at the anode thereof to the cathode of the Schottky diode  62 , a Pch-FET  79  connected at the drain thereof to the cathode of the Schottky diode  62  and also connected in parallel to the Schottky diode  78 , a resistor  81  connected to the resistor  80 , cathode of the Schottky diode  78  and to the source and gate of the Schottky diode  79 , a Zener diode  82  connected at the cathode thereof to the cathode of the Schottky diode  78  and source of the Pch-FET  79  and at the anode thereof to the gate of the Pch-FET  79 , and a capacitor  83  connected to the cathode of the Zener diode  78  and source and gate of the Pch-FET  79 . Note that the resistor  81 , Zener diode  82  and capacitor  83  are connected in parallel to each other. 
     Also, the cable apparatus  60  comprises a fuse  84  connected to the cathode of the Schottky diode  64  and source of the Pch-FET  65 , a fuse  85  connected to the cathode of the Schottly diode  71  and source of the Pch-FET  72 , a fuse  86  connected to the cathode of the Schottky diode  78  and source of the Pch-FET  79 , a terminal a of a connector  87  connected to the fuse  84 , a terminal a of a connector  88  connected to the fuse  85 , a terminal a of a connector  89  connected to the fuse  86 , the terminals a of the connectors  87 ,  88  and  89  being connected to a grounding terminal  92 . 
     Moreover, the cable apparatus  60  comprises a provider flag terminal  90  connected to a provider flag terminal  103  of a power class controller  100  shown in FIG. 10, an FET controller  102  connected to the FET controller  91 , the grounding terminal  92  being connected to the grounding terminal  6 . 
     The cable apparatus having the aforementioned construction functions as will be described below: 
     First, when the cable apparatus-oriented power supply unit  2  has its power supply jack  61  plugged therein, it supplies an internal power to the terminal a of the connector  87  via the power supply jack  61 , Schottky diode  62 , Schottky diode  64  and a parasitic diode of the Pch-FET  65 , and the fuse  84 . 
     At this time, the FET controller  91  will provide a low output. Therefore, the current will not flow from the base to emitter of the transistor  63  and so not from the collector to emitter of the transistor  63 . Since the current will not flow from the resistor  67  to the resistor  66 , it will not flow to the gate of the Pch-FET  65 . 
     Therefore, the current will not flow from the source to drain of the Pch-FET  65  since the latter is off. Namely, the connectors  87 ,  88  and  89  are at a high impedance when the power supply jack  61  is supplying the internal power. 
     Since the terminals a of the connectors  88  and  89  are connected to the power supply jack  61  along the similar route as in the above, when the internal power is supplied, it will be supplied along the same route as for the terminal a of the connector  87 . 
     Next, when the power supply unit  2  for the cable apparatus  60  does not have the power supply jack  61  plugged therein, it will not supply any internal power to the terminal a of the connector  87  along the same route as in the above. In this case, the cable apparatus  60  cannot be supplied with any internal power but is supplied with an external power from each of the connectors, and thus it is in such as to be able to supply and receive the external power between the connectors. Namely, the cable apparatus  60  is not supplied with any internal power from the power supply unit  2  but can be supplied with the external power from the terminal a of the connector  87 . 
     At this time, the FET controller  91  provides a high output. Thus, the current will flow from the base to emitter of the transistor  63 , and so from the collector to emitter. Since the current flows from the resistor  67  towards the resistor  66 , it will also flow to the gate of the Pch-FET  65 . 
     Therefore, the Pch-FET  65  is on, so the current will flow from the source to drain of the Pch-FET  65 . Namely, the connectors  87 ,  88  and  89  are at a low impedance in relation to each other while the internal power is being supplied through the power supply jack  61 . 
     For example when the connector  87  is supplied with an external power, it will supply the external power from the terminal a thereof to the terminal a of the connector  88  via the fuse  84 , source and drain of the Pch-FET  65 , Schottky diode  71 , parasitic diode of the Pch-FET  72  and the fuse  85 , and to the terminal a of the connector  89  via the fuse  84 , source and drain of the Pch-FET  65 , Schottky diode  78 , diode of the Pc-FET  79  and the fuse  86 , respectively. 
     The terminals a of the connectors  88  and  89  can supply and receive an external power between the connectors along the same route as in the above. So, when an external power is supplied, the external power is supplied to each of the connectors along the same route as for the terminal a of the connector  87 . 
     Thus, when an external power is supplied to each of the connectors  87 ,  88  and  89  at the terminal a thereof with an external power, it can be supplied and received between the connectors and delivered to outside from them. 
     Therefore, the connectors  87 ,  88  and  89  can supply and receive a power between predetermined interface devices, namely, between the connectors themselves. 
     Finally, the power class controller  100  will be described in further detail below with reference to FIG.  10 : 
     It should be noted that the power class controller  100  stands for the power class controller  7  having previously been described with reference to FIG.  3 . The malfunction preventive circuit A in FIG. 5 is not shown in FIG.  10 . 
     As shown in FIG. 10, the power class controller  100  comprises a power terminal  101  connected to the power supply unit  4  for the PHY circuit  5 , an FET controller  102  connected to the FET controller  91 , a provider flag terminal  103  connected to the provider flag terminal  90 , a power class output terminal group  104  connected to the PHY circuit  5 , and a grounding terminal  105  connected to the grounding terminal  6 . 
     The power class controller  100  further comprises resistors  150 ,  151  and  152  connected to the provider flag terminal  103  and in parallel to each other, a Zener diode  153  connected at the cathode thereof to the provider flag terminal  103 , and a capacitor  154  connected to the provider flag terminal  103  and in parallel to the Zener diode  153  and which acts to kill any noise developed by the Zener diode  153  in operation. 
     The Zener voltage of the Zener diode  153  should be higher than a voltage dropped across the resistors  150 ,  151  and  152  while being lower than the lowest one prescribed in the IEEE 1394 standard or the voltage from the cable apparatus-oriented power supply unit  2 . 
     In addition, the power class controller  100  comprises a transistor  106  connected at the base thereof to the anode of the Zener diode  153  and capacitor  154 , at the collector thereof to a resistor  107  connected to the power terminal  101 , and at the emitter thereof to the grounding terminal  105 , and a transistor  108  connected at the base thereof to the resistor  107 , at the collector thereof to a resistor  109  connected to the power terminal  101  and at the emitter thereof to the grounding terminal  105 . 
     Moreover, the power class controller  100  comprises jumpers  110 ,  111 ,  112  connected to the power terminal  101 , a jumper  113  connected to the jumper  110  and resistor  107 , a jumper  114  connected to the jumper  111  and a jumper  116  connected to the resistor  109 , a jumper  115  connected to the jumper  112  and a jumper connected to the resistor  109 , a jumper  117  connected to the resistor  109 , and wires  155 ,  156  and  157  connected to the power class output terminal group  104  and in parallel to each other. 
     Note that the PHY controller functions with a power class setting in accordance with the IEEE 1394 standard as having previously been described concerning the second embodiment of the present invention. 
     Four “installed” or “not-installed” states of the components including from the transistor  106  to the jumper  117  of the power class controller  100  will be described below. 
     When the cable apparatus-oriented power supply unit  2  can supply the terminals a of the connectors  87 ,  88  and  89  with an internal power of 15 W, the output of the power class output terminal group  104  is set for an output “001”. 
     When the transistor  106 , resistor  107 , transistor  108 , resistor  109 , and jumpers  114  and  117  are in the installed status while the jumpers  110  to  113  and jumpers  115  and  116  are in the not-installed status, the power class controller  100  will set the power class of “001” for the power class output terminal group  104  to provide a power class output which will allow the cable apparatus-oriented power supply unit  2  to supply an internal power of 15 W to the terminals a of the connectors  87 ,  88  and  89 . 
     The above operation will be described below with reference to FIG.  10 . The provider flag terminal  103  is supplied with an internal power from the cable apparatus-oriented power supply unit  2 . Thus, the voltage is applied to the cathode of the Zener diode  153  and the resistors  150 ,  151  and  152 . Since these resistors  150 ,  151  and  152  are adapted for a small drop of the voltage, this voltage is also applied to the anode of the Zener diode  153 . Since the transistor  106  is applied with the voltage because the anode of the Zener diode  153  is connected to the base of the. transistor  106 , it is turned on. The collector of the transistor  106  will be at the same potential as the grounding terminal  105  since the transistor  106  is on. Therefore, the collector of the transistor  106  takes a potential which will be developed when the power class is set to “0”. 
     Since the transistor  106  is on, the base of the transistor  108  connected to the collector of the transistor  106  is at the same potential as the grounding terminal  105 . Thus, the transistor  108  will be off. The collector of the transistor  108  has the same potential as the power terminal  101  since the power voltage from the power terminal  101  passes through the resistor  109  because the transistor  108  is off Therefore, the collector of the transistor  108  takes a potential which will be developed when the power class is set to “1”. 
     Since the wire  155  of the power class output terminal group  104  is connected to the collector of the transistor  106 , it provides an output “0”. The wire  156  of the power class output terminal group  104  is connected to the grounding terminal  105  via the jumper  114  and thus provides an output “0”. Since the wire  157  of the power class output terminal group  104  is connected to the collector of the transistor  108  via the jumper  117 , it provides an output “1”. 
     Therefore, the power class output terminal group  104  will provide an output “001”, and thus the power class is known to be appropriately set. 
     In case the cable apparatus-oriented power supply unit  2  cannot supply an internal power of 15 W to the terminals a of the connectors  87 ,  88  and  89  depending upon whether the relevant components are in the “installed” or “not-installed” status, the power class output terminal group  104  is set for an output cc “100”. 
     The operation for this setting will be described with reference to FIG.  10 . When the cable apparatus-oriented power supply unit  2  can supply no internal power, the provider flag terminal  103  will not be applied with any voltage. Therefore, the cathode of the Zener diode  153  will have the same potential as the grounding terminal  105  since it is connected to the grounding terminal  105  via the resistors  150 ,  151  and  152 . The transistor  106  will be off because its base is at the same potential as the grounding terminal  105 . Therefore, the collector of the transistor  106  takes a potential which will be developed when the power class is set to “1”. 
     The base of the transistor  108  connected to the collector of the transistor  106  is at the same potential as the power terminal  101  since the power voltage from the power terminal  101  passes through the resistor  107  because the transistor  106  is off. The transistor  108  will be on since it is applied at its base with the power voltage from the power terminal  101 . Thus, the collector of the transistor  108  will be at the same potential as the grounding terminal  105 . Therefore, the collector of the transistor  108  takes a potential which will be developed when the power class is set to “0”. 
     Since the wire  155  of the power class output terminal group  104  is connected to the collector of the transistor  106 , it provides an output “1”. The wire  156  of the power class output terminal group  104  is connected to the grounding terminal  105  via the jumper  114  and thus provides an output “0”. Since the wire  157  of the power class output terminal group  104  is connected to the collector of the transistor  108  via the jumper  117 , it provides an output “0”. 
     Therefore, the power class output terminal group  104  provide an output “100”, and thus the power class is known to be appropriately set. 
     When the power supply unit  2  for the cable apparatus  60  can supply an internal power of 30 W to the terminals a of the connectors  87 ,  88  and  89 , the power class output terminal group  104  is set for an output “010”. 
     When in the power class controller  100 , the transistor  106 , resistor  107 , transistor  108 , resistor  109 , and jumpers  115  and  116  are in the “installed” status while the jumpers  110  to  114  and jumper  117  are in the “not-installed” status, the power class output terminal group  104  is set for an output “010” which allows the cable apparatus-oriented power supply unit  2  to supply the internal power of 30 W to the terminals a of the connectors  87 ,  88  and  89 . 
     The above operation will be described below with reference to FIG.  10 . The provider flag terminal  103  is supplied with an internal power from the cable apparatus-oriented power supply unit  2 . Thus, the voltage is applied to the cathode of the Zener diode  153  and the resistors  150 ,  151  and  152 . Since these resistors  150 ,  151  and  152  are adapted for a small drop of the voltage, this voltage is also applied to the anode of the Zener diode  153 . Since the transistor  106  is applied with the voltage because the anode of the Zener diode  153  is connected to the base of the transistor  106 , it is turned on. The collector of the transistor  106  will be at the same potential as the grounding terminal  105  since the transistor  106  is on. Therefore, the collector of the transistor  106  takes a potential which will be developed when the power class is set to “0”. 
     Since the transistor  106  is on, the base of the transistor  108  connected to the collector of the transistor  106  is at the same potential as the grounding terminal  105 . Thus, the transistor  108  will be off The collector of the transistor  108  has the same potential as the power terminal  101  since the power voltage from the power terminal  101  passes through the resistor  109  because the transistor  108  is off Therefore, the collector of the transistor  108  takes a potential which will be developed when the power class is set to “1”. 
     Since the wire  155  of the power class output terminal group  104  is connected to the collector of the transistor  106 , it provides an output “0”. The wire  156  of the power class output terminal group  104  is connected to the collector of the transistor  108  via the jumper  116  and thus provides an output “1”. Since the wire  157  of the power class output terminal group  104  is connected to the grounding terminal  105  via the jumper  115 , it provides an output “0”. 
     Therefore, the power class output terminal group  104  will provide an output “010”, and thus the power class is known to be appropriately set. 
     In case the power supply unit  2  for the cable apparatus  60  cannot supply an internal power of 30 W to the terminals a of the connectors  87 ,  88  and  89  depending upon whether the relevant components are in the “installed” or “not-installed” status, the power class output terminal group  104  is set for an output “100”. 
     The operation for this setting will be described with reference to FIG.  10 . When the power supply unit  2  for the cable apparatus  60  can supply no internal power, the provider flag terminal  103  will not be applied with any voltage. Therefore, the cathode of the Zener diode  153  will have the same potential as the grounding terminal  105  since it is connected to the grounding terminal  105  via the resistors  150 ,  151  and  152 . The transistor  106  will be off because its base is at the same potential as the grounding terminal  105 . Therefore, the collector of the transistor  106  takes a potential which will be developed when the power class is set to “1”. 
     The base of the transistor  108  connected to the collector of the transistor  106  is at the same potential as the power terminal  101  since the power voltage from the power terminal  101  passes through the resistor  107  because the transistor  106  is off. The transistor  108  will be on since it is applied at its base with the power voltage from the power terminal  101 . Thus, the collector of the transistor  108  will be at the same potential as the grounding terminal  105 . Therefore, the collector of the transistor  108  takes a potential which will be developed when the power class is set to “0”. 
     Since the wire  155  of the power class output terminal group  104  is connected to the collector of the transistor  106 , it provides an output “1”. The wire  156  of the power class output terminal group  104  connected to the collector of the transistor  108  via the jumper  116  provides an output “0”. Since the wire  157  of the power class output terminal group  104  is connected to the grounding terminal  105  via the jumper  115 , it provides an output “0”. 
     Therefore, the power class output terminal group  104  provide an output “100”, and thus the power class is known to be appropriately set. 
     When the cable apparatus-oriented power supply unit  2  can supply an internal power of 45 W to the terminals a of the connectors  87 ,  88  and  89 , the power class output terminal group  104  is set for an output “011”. 
     When in the power class controller  100 , the transistor  106 , resistor  107 , transistor  108 , resistor  109 , and jumpers  116  and  117  are in the “installed” status while the jumpers  110  to  115  are in the “not-installed” status, the power class output terminal group  104  is set for an output of “011” which allows the cable apparatus-oriented power supply unit  2  to supply the internal power of 45 W to the terminals a of the connectors  87 ,  88  and  89 . 
     The above operation will be described below with reference to FIG.  10 . The provider flag terminal  103  is supplied with an internal power from the cable apparatus-oriented power supply unit  2 . Thus, the voltage is applied to the cathode of the Zener diode  153  and the resistors  150 ,  151  and  152 . Since these resistors  150 ,  151  and  152  are adapted for a small drop of the voltage, this voltage is also applied to the anode of the Zener diode  153 . Since the transistor  106  is applied with the voltage because the anode of the Zener diode  153  is connected to the base of the transistor  106 , it is turned on. The collector of the transistor  106  will be at the same potential as the grounding terminal  105  since the transistor  106  is on. Therefore, the collector of the transistor  106  takes a potential which will be developed when the power class is set to “0”. 
     Since the transistor  106  is on, the base of the transistor  108  connected to the collector of the transistor  106  is at the same potential as the grounding terminal  105 . Thus, the transistor  108  will be off. The collector of the transistor  108  has the same potential as the power terminal  101  since the power voltage from the power terminal  101  passes through the resistor  109  because the transistor  108  is off Therefore, the collector of the transistor  108  takes a potential which will be developed when the power class is set to “1”. 
     Since the wire  155  of the power class output terminal group  104  is connected to the collector of the transistor  106 , it provides an output “0”. The wire  156  of the power class output terminal group  104  connected to the collector of the transistor  108  via the jumper  116  provides an output “1”. Since the wire  157  of the power class output terminal group  104  is connected to the collector of the transistor  108  via the jumper  117 , it provides an output “1”. 
     Therefore, the power class output terminal group  104  will provide an output “011”, and thus the power class is known to be appropriately set. 
     In case the cable apparatus-oriented power supply unit  2  cannot supply an internal power of 45 W to the terminals a of the connectors  87 ,  88  and  89  depending upon whether the relevant components are in the “installed” or “not-installed” status, the power class output terminal group  104  is set for an output “100”. 
     The operation for this setting will be described with reference to FIG.  10 . When the cable apparatus-oriented power supply unit  2  can supply no internal power, the provider flag terminal  103  will not be applied with any voltage. Therefore, the cathode of the Zener diode  153  will have the same potential as the grounding terminal  105  since it is connected to the grounding terminal  105  via the resistors  150 ,  151  and  152 . The transistor  106  will be off because its base is at the same potential as the grounding terminal  105 . Therefore, the collector of the transistor  106  takes a potential which will be developed when the power class is set to “1”. 
     The base of the transistor  108  connected to the collector of the transistor  106  is at the same potential as the power terminal  101  since the power voltage from the power terminal  101  passes through the resistor  107  because the transistor  106  is off The transistor  108  will be on since it is applied at its base with the power voltage from the power terminal  101 . Thus, the collector of the transistor  108  will be at the same potential as the grounding terminal  105 . Therefore, the collector of the transistor  108  takes a potential which will be developed when the power class is set to “0”. 
     Since the wire  155  of the power class output terminal group  104  is connected to the collector of the transistor  106 , it provides an output “1”. The wire  156  of the power class output terminal group  104  is connected to the collector of the transistor  108  via the jumper  116  and thus provides an output “0”. Since the wire  157  of the power class output terminal group  104  is connected to the collector of the transistor  108  via the jumper  117 , it provides an output “0”. 
     Therefore, the power class output terminal group  104  provides an output “100”, and thus the power class is known to be appropriately set. 
     Note that the power class controller  100  will provide a signal of a power setting result from the power class output terminal group  104  to the PHY circuit  5  which will in turn control the power supply unit  4  for the PHY circuit  5  based on the result of power class setting. 
     As having been described in the foregoing, the cable apparatus according to the present invention can make a selection between supply of an internal power to a predetermined interface device and that of an external power to the interface device in compliance with the interface standard applied to the predetermined interface device. 
     Thus, the cable apparatus according to the present invention can provide a highly effective power saving since it is adapted such that the power is consumed only when an internal power is supplied via the power line while no power is consumed when an external power is supplied via the power line.