1.  Field of the Invention
This invention relates to a monitor apparatus for an audio-visual system, and more particularly to a monitor apparatus by which selection of one of displayed programs and selection of an operation mode of an audio-visual unit connected thereto can be performed using a pointing device while the screen is watched.  The present invention further relates to a display apparatus by which a controlling menu for selection of a program is displayed on a television receiver or a monitor unit of an audio-visual system. 
2.  Description of the Related Art
Audio-visual systems generally have such a configuration as shown in FIG.  20.  Referring to FIG.  20, the audio-visual system includes an audio-visual monitor unit 171 and three audio-visual units including a video tape recorder (VTR) 173, a laser disk player (LDP) 175 and a video tape recorder 176 integrated with a camera (such video tape recorder will be hereinafter referred to as camcorder).  The video tape recorder 173 is connected to a first audio-visual terminal a of the audio-visual monitor unit 171 by way of an audio-visual cable 178; the laser disk player 175 is connected to a second audio-visual terminal b of the monitor unit 171 by way of another audio-visual cable 180; and the camcorder 176 is connected to a third audio-visual terminal c of the monitor unit 171 by way of a further audio-visual cable 181, so that video signals and audio signals of the video tape recorder 173, the laser disk player 175 and the camcorder 176 may be inputted to the monitor unit 171. 
In the audio-visual system, when a broadcast of, for example, the sixth channel is to be received by means of a tuner of the video tape recorder 173 and displayed on the audio-visual monitor unit 171, the user will first manually operate a remote control unit (not shown) of the video tape recorder 173 to set the tuner of the video tape recorder 173 to the sixth channel.  Then, the user will manually operate a remote control unit (not shown) of the monitor unit 171 to select the first audio-visual input terminal a of the monitor unit 171 while watching the screen of the monitor unit 171. 
With the audio-visual system described above, however, since only characters representing the name of a selected one of the audio-visual input terminals a to c of the monitor unit 171 are displayed on the screen of the monitor unit 171 like "Video 1", even if the user watches the screen of the monitor unit 171, the user cannot know the image of which audio-visual unit the screen displays.  Accordingly, the user must always be aware which audio-visual units are connected to the individual audio-visual input terminals of the monitor unit 171. 
With the conventional audio-visual system, however, selection of an audio-visual unit and selection of a channel are performed separately and are not handled in the same hierarchy.  Further, since only characters representing the name of a selected one of the audio-visual input terminals are displayed on the screen of the monitor unit while the names of the audio-visual units connected to the audio-input terminals of the monitor unit are not displayed, the user must always be aware of the audio-visual units connected to the audio-input terminals of the monitor unit.  Accordingly, the conventional audio-visual system is not superior in user interface. 
A modified audio-visual system is also known and shown in FIG.  21.  The audio-visual system shown is different from the audio-visual system shown in FIG.  20 in that it additionally includes an audio-visual (AV) selector 172.  An output of the audio-visual selector 172 is connected, for example, to the first audio-visual input terminal a of the monitor unit 171 by way of an audio-visual cable 177.  The audio-visual system further includes a tuner 174 as an additional audio-visual unit.  The audio-visual units, that is, the video tape recorder 173, the tuner 174, the laser disk player 175 and the camcorder 176, are connected to input terminals of the audio-visual selector 172 by way of audio-visual cables 178, 179, 180 and 181, respectively.  One of the audio-visual units 173 to 176 is selected by the audio-visual selector 172, and a video signal and an audio signal of the selected audio-visual unit are inputted to the first audio-visual input terminal a of the monitor unit 171. 
In the present audio-visual system, when, for example, a reproduction program of the laser disk player 175 is to be displayed on the monitor unit 171, the audio-visual selector 172 will first be manually operated to set so that the output of the laser disk player 175 may be selected.  Then, the remote control unit (not shown) of the monitor unit 171 will be manually operated to select the first audio-visual input terminal a while watching the screen of the monitor unit 171.  Then, a remote control unit of the laser disk player 175 will be manually operated to set the laser disk player 175 to a reproduction mode. 
With the conventional audio-visual system described above, however, since only characters representing the name of an audio-visual input terminal and an operation mode of the audio-visual unit are displayed on the screen of the monitor unit 171 like "Reproduction of Video 1", even if the user watches the screen of the monitor unit, the user cannot know the image of which audio-visual unit the screen displays.  Further, since a remote control unit is provided for each of the audio-visual units which constitute the audio-visual system, the user cannot select a remote control unit unless the user is aware the image of which audio-visual unit the user watches. 
In order to solve this problem, audio-visual systems have been developed wherein manually operable keys for controlling a plurality of audio-visual units are disposed on a housing of a single remote control unit or wherein a change-over switch for audio-visual units is provided so that one manually operable key is used commonly for a plurality of audio-visual units.  However, since the problem that the audio-visual units cannot be controlled by means of the manually operable keys unless the user is aware the image of which audio-visual unit the user watches at present remains unsolved, the audio-visual system is difficult to use where it involves a large number of audio-visual units. 
Meanwhile, various displaying apparatus for displaying a control menu for a television receiver are already known.  One of the control menu displaying apparatus is shown in FIG.  22.  Referring to FIG.  22, when a power source switch not shown of a television receiver not shown is turned on, a control window 143 is displayed at a left end portion of a screen 141 of the television receiver, and icons 144 to 149 of a control menu for selecting a channel to be received are displayed in the control window 143.  If one of the icons 144 to 149 is selected in this condition using a remote control unit or a pointing device such as a mouse not shown, then a program of the selected channel is received and an image is displayed in a major area 142 of the screen 141.  During reception of a program, the control window 143 may be erased by manual operation of the remote control unit or the like to expand the area in which the image of the received program is displayed.  It is to be noted that a further area 150 below the major area 142 and the control window 143 is used to display therein, for example, a displayed condition of the received channel in the form of a caption.  Also the area 150 may be used to display part of the image of the received program therein. 
With the conventional control menu displaying apparatus, if the total number of items of programs constituting the menu is comparatively small, then all of them can be displayed in the control window 143.  However, when it is tried to select one of a large number of channels, for example, 100 channels or more such as in the case of cable television, they cannot be displayed at a time on the screen 141 at all.  In this case, such a measure as to scroll the menu in the control window is necessary.  Consequently, although those channels which are enjoyed comparatively frequently by the user of the television receiver are settled to some degree, the menu must be scrolled every time until a desired channel is displayed, and accordingly, much time is required for selection of the menu.