referring to the figures , exemplary embodiments of the invention will now be described . the exemplary embodiments are provided to illustrate the invention and should not be construed as limiting the scope of the invention . consider a case where a digital television ( dtv ) receives an audio / video signal via a digital satellite - broadcasting receiver . fig1 illustrates an exemplary arrangement of a signal transmitting system which includes two electronic devices , i . e ., a dss - ird ( digital satellite system integrated receiver decoder ) 11 and a digital tv ( dtv ) 12 . in this embodiment of the present invention , these devices are connected to each other by an ieee1394 digital interface cable 14 as well as an analog video / audio cable 16 . the digital interface cable 14 is based upon the ieee1394 standard for a high - performance serial bus , and provides a peer - to - peer interface between various digital peripherals with up to 63 isochronous digital communication channels . the ieee1394 digital interface 14 is capable of carrying digital video / audio signals in various digital formats , such as the dvi format and mpeg1 / 2 formats . assuming that both the dss - ird 11 and the dtv 12 are also based upon the ieee1394 standard , the digital interface cable 14 allows a digital video / audio signal from the dss - ird 11 to be transmitted to the dtv 12 . in addition to the digital interface 14 , the analog audio / video cable 16 is provided between the dss - ird 11 and the dtv 12 , because both a digital signal and an analog signal can be provided from the dss - ird 11 . the dss - ird 11 is a satellite broadcasting receiver based upon the dss standard , which is one of the standards for satellite broadcasting in the united states . according to the dss standard , an audio / video signal is digitized and coded in the mpeg2 format , which is one of the global standards for video compression . the coded signal including program - related information is transmitted in two original modes of the dss standard , i . e ., sd ( standard definition ) and hd ( high definition ). the sd mode is designed for transmitting an mpeg2 signal in a standard quality , whereas the hd mode is for high - quality transmission . since the sd mode is the dss &# 39 ; s unique mode , a dss - sd decoder is required to decode a signal transmitted in this mode . the hd mode is , on the other hand , partly based upon the atsc ( advanced television systems committee ) system , which is used for surface digital broadcasting in the united states . to decode a signal transmitted in the hd mode , an atsc decoder may be used . under such a circumstance , the dss - ird 11 will not need to have an expensive dss - hd decoder , if the dtv 12 with a built - in atsc decoder is provided with a decoding function for dss - hd signals . in this case , signals can be transmitted to the dtv 12 in different formats . namely , a dss - sd signal received at the dss - ird 11 is decoded into an analog signal in the dss - ird 11 , and then the analog signal is transmitted to the dtv 12 via the analog video / audio cable 16 . a dss - hd signal is , meanwhile , received at the dds - ird 11 and is transmitted through the digital interface cable 14 to the dtv 12 . the digital signal is then decoded in the dtv 12 into an analog signal . fig2 and 3 illustrate exemplary arrangements of the dss - ird 11 and the dtv 12 , respectively . as shown in fig2 , the dss - ird 11 includes a dss - sd / hd receiver 114 , a dss - sd decoder 116 , a digital input / output terminal 110 , and an analog output terminal 112 , and an ieee1394 interface 121 , and a memory 151 . it is noted that the dss - ird 11 does not have a dss - hd decoder but only the dss - sd decoder 116 . the memory in the present embodiment is provided in configuration rom ( read only memory ). however , one skilled in the art will recognize that other storage devices may be used . the receiver 114 , connected to an antenna 118 , is capable of receiving both dss - sd and dss - hd signals from a satellite . these digital signals received at the receiver 114 will be supplied to the digital input / output terminal 110 . in addition , the receiver 114 also provides the digital signals to the dss - sd decoder 116 , which decodes the dss - sd signal into an analog audio / video signal . when a dss - sd signal is being received , therefore , the dss - sd decoder 116 will supply to the analog output terminal 112 an analog audio / video signal , which is derived from the digital signal . as shown in fig3 , the dtv 12 has a digital input / output terminal 120 , an analog input terminal 122 , an hd decoder 124 , a monitor 126 including a display and speakers , an ieee1394 interface 141 , a switch 128 for selecting an input terminal , and a selector 130 including a controller 140 to control the switch 128 , and a memory 160 . the memory in the present embodiment is provided in configuration rom ( read only memory ). however , one skilled in the art will recognize that other storage devices may be used . as illustrated in fig1 , the digital input / output terminal 120 communicates with the digital input / output terminal 100 of the dss - ird 11 via the digital interface cable 14 , so that it receives both dss - sd and dss - hd signals from the dss - ird 11 . the analog input terminal 122 is connected to the analog output terminal 102 by the analog video / audio cable 16 , so that an analog audio / video signal can be received . within the dtv 12 , the hd decoder 124 decodes an incoming dss - hd signal transmitted through the digital interface cable 14 that arrives at the digital input terminal 120 and passes through the ieee1394 interface 141 . when an hd signal is transmitted from the dds - ird 11 , the hd decoder 124 will decode the digital signal into a corresponding analog audio / video signal , which will be generated on the monitor 126 , and supply it to a first terminal “ a ” of the switch 128 . an analog audio / video signal is also obtained at the analog input terminal 122 , when a dss - sd signal is being received at the dss - ird 11 . the analog audio / video signal , which is decoded by the dss - sd decoder 116 of the dss - ird 11 , is provided to a second terminal “ b ” of the switch 128 . accordingly , an analog audio / video signal will be supplied from either the terminal “ a ” or “ b ” to the monitor 126 via a third terminal “ c ” of the switch 128 . the controller 140 controls the switch 128 based upon the dtv &# 39 ; s capability of decoding an incoming digital signal . more specifically , the controller 140 monitors the output of the hd decoder 124 , and will control the switch 128 to select its first terminal “ a ” if the hd decoder 124 provides an analog audio / video signal , otherwise will direct the switch 128 to select its second terminal “ b .” each device can have a capability list . the capability list may be stored in a device &# 39 ; s memory . the memory in the present embodiment is provided in configuration rom ( read only memory ). however , one skilled in the art will recognize that other storage devices may be used to store a capability list . since configuration rom typically does not have much room to store information , e . g . 1024 bytes , keywords or brief information may be stored . therefore , to store detailed information , additional memory units can be used . such capability information may be stored using a descriptor based upon the ieee1394 standard p1212r 64 - bit fixed addressing . a descriptor is a leaf ( a contiguous information field pointed to by a configuration rom directory entry ) that provides additional information to describe an object associated with a directory entry in configuration rom . devices may inquire into the capabilities of other devices by issuing a command on the ieee1394 digital interface 14 to receive capability information . the queried device then responds to the inquiry command and will send the information to the device that issued the query command on the ieee1394 digital interface 14 . two examples of a capability list are illustrated in fig5 and 6 , for ird and dtv capabilities , respectively . in the case of dtv , since each device has a capability list , dtv can select compatible devices according to the information in their capability list . once the device is selected , the dtv establishes an isochronous connection . depending upon the selected device &# 39 ; s status , the selected device may output a signal onto the ieee1394 digital interface 14 where the dtv picks up the signal . the output signal from the selected device has a field to indicate the signal format type . the format type , which may be changed dynamically , depends on the contents or situation of the device . for example , a digital vhs can play mpeg2 , dss and analog . the dtv keeps monitoring the signal format field to determine whether to process the signal or not . this is a second stage of determination . for instance , if the signal is mpeg2 , a selector 130 enables hd decoder 124 and selects switch “ a ” to feed the signal to a monitor 126 . if the signal is analog , the selector 130 selects switch “ b .” if the signal is such that it is not compatible for this particular dtv , dv for example , then selector 130 may disable hd decoder 124 . the operation of the dtv 12 will be described with reference to fig4 . fig4 illustrates an operation of the transmission system step by step . in fig4 , the column “ situation ” shows a format of the signal transmitted from the dss - ird 11 . the column “ action by user ” indicates the action that a user of the system is taking . let us assume that the user is watching a satellite tv program received at the dss - ird 11 on the dtv 12 . the column “ signal flow ” in fig4 shows a signal flow from the dss - ird 11 to the dtv 12 and the channel through which the signal is being transmitted . based on the ieee1394 standard , the digital interface cable 14 provides up to 63 isochronous digital communication channels , and allows more than two devices to communicate with each other . these channels are denoted by “ ch63 ,” “ ch x ” and “ ch y ” in fig4 . video / audio cable 16 provides a communication channel for an analog signal . for the case of a digital signal , the channel is assigned dynamically . for the case of an analog signal , unlike the digital signal , once it is connected , there is no dynamic assignment . the columns “ ird ” and “ dtv ” indicate the operations or workings of the ird 11 and the dtv 12 , respectively . assume that the dss - ird 11 has been selected by the user to supply an input signal to the dtv 12 . the dss - ird 11 is receiving a dss - hd signal at this stage . an isochronous communication , called “ point - to - point ” connection , has been established between the dss - ird 11 and the dtv 12 . receiving a dss - hd signal , the dss - ird 11 is transmitting to the dtv 12 the digital signal in the mpeg2 - hd format through one of the digital communication channels , “ ch x ,” as illustrated by an arrow . within the dtv 12 ( refer to fig3 ), the incoming digital signal is input to the hd decoder 124 to be decoded into the analog video / audio signal , which the monitor 126 can cope with . the analog output of the hd decoder 124 is then being supplied to the terminal “ a ” of the switch 128 . since the incoming digital signal is in the hd format , which the dtv 12 is capable of decoding , the switch 128 is making a connection between its terminals “ a ” and “ c .” accordingly , the video / audio signal decoded by the hd decoder 124 is being supplied to the monitor 126 . the format that the dss - ird 11 receives has changed , and the dss - ird is now receiving a dss - sd signal . the dss - ird 11 decodes the digital signal in the mpeg2 - sd format to an analog signal using its sd - decoder 116 , and the analog signal is provided to its analog output terminal 112 , so that it is transmitted to the dtv 12 through the analog audio / video cable 16 . at the same time , the digital signal in the mpeg2 - sd format is provided to the digital input / output terminal 110 and transmitted to the dtv 12 via the digital interface cable 14 . the dtv 12 receives the digital signal in the mpeg2 - sd format and the analog signal at the digital input / output terminal 120 and the analog input terminal 122 , respectively . since the dtv 12 only has a hd decoder 124 , the digital signal is in an ineligible format . within the dtv 12 , therefore , the hd decoder 124 can no longer provide a usable signal for the monitor 126 . nevertheless , the dtv 12 examines the format of the incoming digital signal and , as it recognizes that it is receiving a digital signal , switches to the analog input terminal 122 from its digital input / output terminal 120 . more specifically , the controller 140 controls the switch 128 based upon the dtv &# 39 ; s capability of decoding an incoming digital signal . the controller 140 sends a command to the switch 128 to select the second terminal “ b .” as a result , the analog signal , which is being decoded in the dss - ird 11 and provided to the analog input terminal 122 , is directed to the monitor 126 through the connection between the terminals “ b ” and “ c .” accordingly , the video / audio signal will be provided to monitor 126 in an eligible format even after the format of the transmitted signal has changed . therefore , the user of the system does not have to manually select the input terminal . moreover , in the preferred embodiment of the present invention , the digital signal is provided to the digital input / output terminal 120 of the dtv 12 , after the switch 128 makes a connection between terminals “ b ” and “ c .” in other words , the format of the digital signal will be examined while the analog signal received at the analog input terminal 122 is being directed to the monitor 126 . the input terminal of the dtv 12 will , therefore , be switched back to its digital input / output terminal 120 when the digital signal in the dss - hd format is transmitted again . the operation explained above will be particularly effective where the format of the transmitted signal changes between digital and analog . a digital signal and an analog signal that have been recorded on a single medium are played back in a digital vhs ( dvhs ) system a dv signal is provided to a digital tv that is incapable of decoding the dv format . the present invention can also allow digital equipment to be used even if a digital signal is provided in a format that is unknown when the device is designed . the embodiments of the invention described above are , of course , subject to other variations in structure and implementation . for instance , additional devices may be inserted between various nodes , terminals , and devices in the above embodiments without materially changing their overall function . in general , the scope of the invention should be determined not by the embodiments illustrated but by the appended claims and their legal equivalents .