1. Field of the Invention
The present invention relates to a way of structuring input/output plugs and a digital interface for equipment in a communications system where a number of equipment are capable of multiplexing and transferring packets of control signals and information signals via a bus.
2. Description of the Related Art
In conventional communication systems where AV (Audio/Video) equipment such as, for example, Video Tape Recorders (hereinafter referred to as VTRs), Televisions (hereinafter referred to as TVs) etc. are connected together via analog AV signal lines and digital control signal lines, a D2B (Domestic Digital Bus) has been used. Examples of this kind of system are described in the European patents that belong to the same applicant relating to this kind of communications system.
First, a description will be given of an example of this kind of communications system with reference to FIG. 17. This communications system comprises a TV, a VTR 1, a VTR 2, a Multi Disc Player (hereinafter referred to as an MDP), and an editor. The VTR 2 is also connected to a device, which is not compliant with a digital control signal line (hereinafter referred to as a non-bus compliant device).
The AV signal input/output plug for the non-bus compliant device is connected to input/output plugs of other devices via analog AV signal lines, wherein the plugs are marked only with designation numbers P1, P2 and P3, protruding directly out from units known as switchboxes (SW box). Commands such as connection control commands are sent and received by other devices via analog AV signal lines and digital control signal lines, which are connected separately from AV signal lines. Each of the equipment is also comprised of one or more functional units, which in the case of a VTR would be (i) a deck for recording and playing back and (ii) a tuner for selecting the signal to be received, and in the case of a TV, would be (i) a monitor and (ii) an amplifier. There is also an AVC (Audio/Video Controller) for controlling the operation of all of the items of equipment, although this is not shown in the diagrams. In the following description, these functional units may also be referred to as sub-devices.
Control connection can be carried out in two ways in a communications system structured in this way. These two ways, which will be referred to as connection control method 1 and connection control method 2, will be described below in numerical order.
In connection control method 1, information pertaining to the connection structure for each device, i.e. which plug is connected to an opposite equipment and whether plugs are used for input or output, is pre-set by the user. In this way, when the equipment is receiving the connection control command, the sub-device which is to be the AV signal source is connected to an output plug being considered as the destination. Alternatively, a path may be set up within the device between the input plug of the designated number and the appropriate output plug, then a command is transmitted to the device connected to the output plug. The object is then achieved at the point in time when the command reaches the sub-device within the specific device indicated by the destination. At this time, commands are not transmitted via the control signal line when the device is a non-bus compliant device. The plug numbers for devices connected to this kind of device have to be directly specified (for example, in the case in FIG. 17, the input plug P1 for the VTR 2 is specified).
The following is a description with reference to FIG. 18 of the sequence in connection control method 1 when an MDP output is recorded on a VTR 2 as a result of instructions from an editor. FIG. 18(a) shows the communications sequence and FIG. 18(b) shows the commands.
First, the MDP receives a command giving an instruction to connect the deck output to the deck of the VTR 2 from the command master (editor) (communication 1). At this time, none of the output plugs of the MDP are connected to the VTR 2. However, the output plug P3 is connected to the input plug P1 of the VTR 2, so a command is sent to the VTR 1 via a path from the input plug P1 to the switchbox (communication 2).
When the VTR 1 receives this command, none of the output plugs are connected to the VTR 2 but the output plug P3 is connected to the input plug P1 of the TV. A command is sent via a path from the input plug P1 via the switchbox to the TV (communication 3).
When the TV receives this command, it is understood that the output plug P3 is connected to the input plug P2 of the VTR 2 and a command is sent to the VTR 2 from the input plug P2 via the deck (communication 4).
The VTR 2 then receives this command and switches the switchbox connection so as to input from the input plug P2 to the deck. Once the VTR 2 completes the process 4, the TV is notified of the process completion. Upon receiving this notification, the TV gives notification to the VTR 1 that the process 3 is completed. When the VTR 1 then receives the notification, it gives notice to the MDP that the process 2 has been completed. Upon receiving this notification, the MDP gives notice to the command master that the process is completed. These packets are omitted from the diagrams.
Here, an editor has been set up as the command master. However, rather than setting an editor up on the communications system, a structure may be adopted where the MDP and the VTR have command master functions.
In a second connection control method, an equipment being central (in the following, this is an AV center) manages all of the connection information regarding which kinds of equipment are connected together via which numbered ports in which directions. If the AV center receives a command requesting AV signal connection via the digital control signal line, it sends this command via the digital control signal line to the target device. The target device then receives this command and performs the input/output selection. At this time, it is possible to designate the sub-device by category via the initial connection request from the command master (by BS, CS etc. which are more in line with the objectives, rather than by a tuner etc.). However, at the time of a connection request, only designation of its own plug is available because of it is only aware of its own plug structure.
The following is a description with reference to FIG. 19 of the sequence in a connection control method 2 when a TV is taken-as an AV center and output from an MDP is recorded by a VTR 2. Here, FIG. 19(a) shows the communications sequence and FIG. 19(b) shows the commands.
First, the TV receives a command from the command master instructing it to connect the MDP deck output to the deck of the VTR 2 (communication 1). The TV then receives this command and sends a command to the MDP to the effect that the output for the deck sub-device is to be outputted from the output plug P3 (communication 2).
If the MDP receives this command, the switchbox is switched so that the deck output is connected to the output plug P3 and notification of the completion of the switching process is then sent to the TV. If the TV then receives this information, a command is sent from the input plug P1 via the output plug P3 to the VTR 1 (communication 3).
If the VTR 1 receives this command, the switchbox is switched so that a connection is made from the input plug P1 to the output plug P3 and notification of completion of the switching process is sent to the TV. If the TV then receives this notification, a command is sent from the input plug P2 to the deck to be inputted to the VTR 2 (communication 4).
Providing the VTR 2 receives this command, the switchbox is switched so as to input from the input plug P2 to the deck. The TV is then notified when the switching process is complete.
If the TV then receives notification of completion from the VTR 2, notification of completion of the connection is sent to the command master.
However, with connection control method 1, the digital control signal line becomes congested as a result of commands being transmitted between the equipment, which neighbor each other. An infinite loop may be formed depending on the settings of the equipment in the connection line. It is also necessary to know the structure of the equipment, which command master intends to control and the structure of the connections among the equipment in the overall system, so as to designate the plug numbers.
Also, in connection control method 2, no matter how simple a connection is made between a plug and the equipment to which the plug is connected, this may not be achieved without a request being made to the AV center. Further, designation can be made using the sub-device category at the time of a connection request, but plug designation can only be achieved for the equipment's own plugs, for which the structure is known.
It is therefore apparent that connection control of a variety of AV signals by holding connection information for input/output-plugs as interfaces with external equipment is not ideal. It is therefore the object of the present invention to provide a communications system capable of resolving these kinds of problems.