Priority switching apparatus of input signal for a display apparatus

Abstract: An input signal from a Dsub connector and BNC connectors is selected by an analog switch (1, 2). The frequency of horizontal and vertical synchronizing signals applied from one connector end is measured by a synchronizing frequency detection circuit (4). The frequencies of horizontal and vertical synchronizing signals applied from the other connector end are converted into voltage values by F/V converters (6, 7). A microcomputer (8) determines the presence of a synchronizing signal and selects an input signal from the connector end of a high priority level set in a non-volatile memory (10).

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to priority switching apparatuses of an input signal. More particularly, the present invention relates to a priority switching apparatus of an input signal that can automatically switch among input signals applied to respective input terminals in a monitor display device including a plurality of input terminals. Description of the Background Art The spread of personal computers in these days is remarkable. The color display monitors connected to these personal computers are provided with various functions. One such function is an input switching function. BNC connectors and a Dsub connector are provided at the back side of the display. Input signals that are applied to these connectors can be switched by a switch that is provided at the front side of the display. A BNC connector is connected individually to a coaxial cable for each video signal of R, G, and B, and to horizontal and vertical synchronizing signals respectively. The Dsub connector includes a plurality of pins. The coaxial cable of each video signal of R, G, and B and horizontal and vertical synchronizing signals is connected to the pins of the Dsub connector. A system is proposed in Japanese Patent Laying-Open No. 6-51729 wherein an input signal path with a synchronizing signal is automatically detected and switched to even when a plurality of input terminals are connected. A display employing such a method can be installed in dealing rooms of banks and securities companies. The display may be used as a monitor of a word processor, and switched, if necessary, to display stock information, for example. However, a limitation exists in that the switch of the display must be effected every time to confirm whether stock information is displayed or not. In other words, a change in the signal that is not displayed cannot be identified in real time. Information cannot be obtained instantaneously when used in dealing systems and the like. In order to automatically switch the input of the display when stock information, for example, is input as input signals, the switching circuit disclosed in the aforementioned Japanese Patent Laying-Open No. 6-51729 detects the frequency of a synchronizing signal of an input signal of another terminal when the currently selected input terminal does not have a synchronizing signal, and the input signal path is automatically switched. However, the path cannot be switched to another input signal path if a synchronizing signal is applied to the selected input terminal. US-A-4,954,880 describes a colour display apparatus interfacing a CRT colour display with one of two inputs: a first input with separate signal lines for synchronizing pulses; and a second input for receiving video signals on which the synchronizing pulses are superimposed. The composite sync signal video signal input is given priority whenever present. SUMMARY OF THE INVENTION It would be desirable to provide a priority switching apparatus of an input signal to switch among inputs according to its priority by assigning a priority level to each of a plurality of input terminals. The present invention is set out in the appended claims. According to an aspect of the present invention, a priority level is defined for each of the plurality of input terminals. The input of a synchronizing signal is detected, and an input terminal of high priority is selected. Therefore, the information applied to the selected input terminal can be immediately provided on a display. According to a preferable embodiment of the present invention, a priority level is set for each input terminal by a priority level setting circuit. According to a further preferable embodiment of the present invention, a synchronizing signal is detected by detecting the frequency of the horizontal and vertical synchronizing signals. The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a block diagram of an embodiment of the present invention. Fig. 2 is a flow chart for describing a specific operation of the embodiment of the present invention. Figs. 3A and 3B are diagrams indicating the relationship between a frequency of a horizontal synchronizing signal and a converted voltage value. Figs. 4A and 4B are diagrams showing the relationship between a frequency of a vertical synchronizing signal and a converted voltage value. DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to Fig. 1, a Dsub.B signal and a BNC.B signal, a Dsub.R signal and a BNC.R signal, a Dsub.G signal and a BNC.G signal, a Dsub.H signal and a BNC.H signal, and a Dsub.V signal and a BNC.V signal are applied to an analog switch 1. The synchronizing signals, which can be used in the present invention, include a sync-on green signal having horizontal and vertical synchronizing signals added to a video signal G, a composite sync signal having a vertical synchronizing signal added to a horizontal synchronizing signal, and separate sync signals which are respectively independent horizontal and vertical synchronizing signals. Analog switch 1 responds to a switching signal 1 from a microcomputer 8 which will be described afterwards to switch between an input from BNC connectors and an input from a Dsub connector to separate an input signal into video signals R, G, B, and signals C.SYNC (Composite Sync), H.SYNC and V.SYNC. Signals C.SYNC, H.SYNC and V.SYNC are provided to a synchronizing processor 3. The Dsub connector includes fifteen, for example, input pins to which signals Dsub.B-Dsub.V are applied. Synchronizing processor 3 generates a horizontal drive signal HD and a vertical drive signal VD which are sent to a deflection system, and a horizontal synchronizing signal HS, a vertical synchronizing signal VS, and a synchronization information signal having the polarity arranged. Signals HS and VS and the synchronization information signal are applied to a synchronizing frequency detection circuit 4. Synchronizing frequency detection circuit 4 measures the frequencies of signals HS and VS to provide the frequency detecting signal to microcomputer 8. Signals Dsub.G and BNC.G, signals Dsub.H and BNC.H, and signals Dsub.V and BNC.V are also applied to an analog switch 2. Analog switch 2 responds to a switching signal 2 from microcomputer 8 to switch between the inputs from the BNC connector and the Dsub connector to generate and provide to a synchronizing processor 5 signals C'SYNC, H'SYNC and V'SYNC. Synchronizing processor 5 generates a horizontal synchronizing signal H'S and a vertical synchronizing signal V'S which are applied to F/V converters 6 and 7, respectively. F/V converters 6 and 7 set equal the respective pulse widths of signals H'S and V'S to integrate the pulses for conversion into a DC voltage. The DC voltage is applied to an A/D port of microcomputer 8. Microcomputer 8 determines change in the frequency according to a detection signal from synchronizing frequency detection circuit 4 and the voltage values applied from F/V converters 6 and 7. A switch 9 for setting the priority level and a non-volatile memory 10 for storing the current selected state of an input signal are connected to microcomputer 8. Switch 9 can be selectively set using on screen display. A specific operation of the embodiment of the present invention will be described hereinafter with reference to Figs. 1-4. Microcomputer 8 provides switching signals 1 and 2 to select a port (input terminal) stored in non-volatile memory 10 at step (abbreviated as "SP" in the figure) SP1 of Fig. 2. It is assumed that analog switch 1 selects the Dsub connector end by switching signal 1, and analog switch 2 selects the BNC connector end by switching signal 2. Signal C.SYNC or signals H.SYNC and V.SYNC are generated according to a signal from the Dsub connector selected by analog switch 1 to be provided to synchronizing processor 3. Synchronizing processor 3 provides signals HD, VD, HS, VS, and a synchronization information signal according to an input synchronizing signal. Signals HS and VS and the synchronous information signal are applied to synchronizing frequency detection circuit 4. Microcomputer 8 causes synchronizing frequency detection circuit 4 to detect the synchronizing signal in response to the current selection of a signal from the Dsub connector at step SP2. When the synchronizing signal is detected at step SP3, it is determined whether a priority level is set for the Dsub connector at step SP4. It is determined that a priority level is set if switch 9 is closed. When microcomputer 8 determines that a priority level is set, it is determined whether the priority level of the selected Dsub connector is high or not at step SP5. If the priority level is high, control proceeds to step SP6 where the currently selected information is stored in non-volatile memory 1. The operation of steps SP1-SP6 is executed repeatedly thereafter. If it is determined that the priority level is not high at step SP5, control proceeds to steps SP7 where the input signal of the BNC connector which is the opposite port is measured. More specifically, analog switch 2 selects a signal of the BNC connector end, which is applied to synchronizing processor 5. Signals H'S and V'S provided from synchronizing processor 5 are integrated by F/V converters 6 and 7. Here, the relationship between the frequencies of signals H'S and V'S and the voltage value is as shown in Figs. 3A, 3B, 4A and 4B. As shown in Fig. 3A, the frequency of a horizontal synchronizing signal corresponds to 20kHz-100kHz. Conversion of these frequencies into voltage values is shown in Fig. 3B. Referring to Fig. 4A, the frequency of a vertical synchronizing signal corresponds to 40Hz-160Hz. Conversion of these frequencies into voltage values is shown in Fig. 4B. When microcomputer 8 determines that there is an input signal from the opposite port, i.e., from the BNC connector, at step SP8, control proceeds to step SP9 where the input of the BNC connector end is selected by analog switch 1 and the input signal of the Dsub connector end is selected by analog switch 2. According to an embodiment of the present invention, determination and switching of a signal can be effected instantaneously since the frequencies of synchronizing signals of two systems are continuously monitored. Unnecessary switching will not be carried out since the frequencies of the horizontal and vertical synchronizing signals can be measured. An intelligent control is possible since switching is not forced by means of hardware. Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the scope of the present invention being limited only by the terms of the appended claims.

Claims: A priority switching apparatus for switching among input signals applied to a plurality of input terminals, said switching apparatus comprising: synchronizing signal detection means (4) for detecting a synchronizing signal, when included, in an input signal applied to said plurality of input terminals, and switching means (1, 2) responsive to the detection of a synchronizing signal by said synchronizing signal detection means for selecting an input terminal to which said synchronizing signal is applied, and providing an input signal applied to that input terminal, characterised in that said switching means is responsive to the detection of a high priority level, which is selectable for each of said plurality of input terminals, to select an input terminal for which said high priority level is selected. A priority switching apparatus according to claim 1, further comprising priority level setting means (9) for setting a priority level for said input terminals. A priority switching apparatus according to claim 1 or 2, further comprising a non-volatile memory for storing information identifying the input terminal for which the input signal is currently provided. A priority switching apparatus according to claim 1, 2 or 3, wherein said synchronizing signal detection means detects a frequency of horizontal and vertical synchronizing signals. A priority switching apparatus according to any preceding claim, wherein said input terminals comprise a BNC connector and a Dsub connector. A method of selecting an input signal of an image to be displayed on a display device having a plurality of selectable signal input paths, comprising the steps of: monitoring for an input signal on a second input signal path, during receipt of an input signal on a currently selected first input signal path, to produce a switching signal on detection thereof; and selecting said second input signal path in response to said switching signal, characterised in that said method further comprises: selectively assigning a priority level to the first and second input signal paths, one of said paths having a high priority level; detecting whether the first or the second input signal path has said high priority level; and selecting the second input signal path in response to said switching signal if the second input signal path has said high priority level, or maintaining said current selection of the first input signal path if the first input signal path has said high priority. The method of claim 6, further comprising storing, information identifying the new currently selected input terminal in non-volatile memory. The method of claim 7, wherein each input signal includes a synchronizing signal, and the detecting of whether an input signal is present on said second input signal path comprises detecting whether a synchronizing signal is present on said second input signal path. The method of claim 8, wherein the synchronizing signal comprises horizontal and vertical synchronizing signals, and wherein the detecting of whether a synchronizing signal is present comprises detecting a frequency of the horizontal and vertical synchronizing signals. The method of any of claims 6 to 9, wherein the first input signal path comprises a BNC connector and the second input signal path comprises a Dsub connector.

Inventors: HIRAKA TADAHIKO, SAKAI YOSHIKAZU, SAKUDA JUNJI, HIRAKA, TADAHIKO, SAKAI, YOSHIKAZU, SAKUDA, JUNJI, Hiraka, Tadahiko, Nanao Corp., Sakai, Yoshikazu, Nanao Corp., Sakuda, Junji, Nanao Corp.
Applicants: NANAO CORP, NANAO CORPORATION
Application year: 1996
Main classification: G09G5
IPC codes: G09G5, H03K17, H04N5, G09G1