JPH0429071B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a device that is interposed in a system of a monitor television and a computer and performs signal processing such as screen composition between the system and external video equipment. (Prior Art) Conventionally, devices have been provided that have new functions such as superimposing a video signal and an RGB signal. For example, in a system consisting of a monitor TV and a computer, there is a mode in which only RGB signals are displayed on the monitor TV (CPU mode), a mode in which only video signals are displayed on the monitor TV (video mode), a mode in which the video signal and RGB signal are superimposed, and the same It is possible to select a mode in which images are displayed simultaneously on the screen (superimpose mode). (Problem to be solved by the invention) However, in this type of system, when the superimpose mode is selected, a horizontal synchronization signal and a vertical synchronization signal are sent from the monitor TV side to the computer side in accordance with the synchronization signal of the NTSC signal. When in CPU mode, a synchronization signal generated within the computer is supplied to the monitor TV. On the other hand, recently, a video conversion device (referred to as a terotspa) has been provided which is installed as an intermediary in these systems and processes an external video signal and the RGB signal. Since synchronization signals based on external video signals are supplied, it is necessary to adjust these synchronization signals. For example, when a computer is in CPU mode and a video conversion device is synchronizing using a synchronization signal or burst signal generated by a synchronization signal generator installed in the device, the computer mode is changed to superimpose mode. In this case, the RGB signal output from the computer is synchronized with the synchronization signal supplied from the monitor TV, resulting in an image with disrupted color synchronization. Therefore, the user must perform a switching operation of a changeover switch provided in the video conversion device to switch between external synchronization and internal synchronization, which is extremely troublesome. (Means for Solving the Problems) The video conversion device of the present invention is implemented in a system having at least a superimpose function for superimposing a video signal and an RGB signal from a computer and projecting the superimposed image on the screen of a monitor television. The device has a mode in which only the RGB signal is displayed on the screen, a mode in which only the external video signal input from an external video device is displayed on the screen, and a mode in which the RGB signal and the external video signal are superimposed. RGB output from the computer
A changeover switch is provided for switching between an external synchronization mode in which the signal is output in synchronization with the external video signal and an internal synchronization mode in which the signal is output in synchronization with the synchronization signal and burst signal generated within the device, and
A mode for switching to external synchronization mode regardless of the switching state of the changeover switch by detecting a horizontal synchronization signal of an NTSC signal supplied from the monitor TV side to the computer side when superimpose is selected by the computer. A detection circuit is provided. (Function) When the superimpose mode is commanded by the computer, horizontal and vertical synchronizing signals of NTSC signals are supplied from the monitor television to the computer via the video converter. The mode detection circuit detects the horizontal synchronization signal output from this monitor television. At this time, even if the changeover switch provided in the video conversion device to switch between external synchronization and internal synchronization has been switched to the internal synchronization side, the mode detection circuit changes the changeover switch based on the detected horizontal synchronization signal. Regardless of the switching state, it automatically switches to external synchronization, which outputs the video signal in synchronization with the video signal input to the video conversion device. (Example) Examples of the present invention will be described below with reference to the drawings. FIG. 1 shows a connection state between a video conversion device 1, a monitor television 2, and a computer 3 according to the present invention. Monitor TV 2 outputs horizontal synchronization signal HD and vertical synchronization signal VD in accordance with the NTSC signal synchronization signal.
are supplied to the computer 3, and these synchronization signals become synchronization signals when the computer 3 selects the superimpose mode. On the other hand, the vertical synchronization pulse from computer 3
V _SYNC , horizontal synchronizing pulse H _SYNC and RGB signals are input to the monitor television 2 via the video conversion device 1 . These synchronization pulses are signals output to the monitor television 2 when the computer 3 selects the CPU mode. The video conversion device 1 converts between the RGB signal input from the computer 3 and the external video signal input from an external video device (not shown) the CPU mode, video mode, and superimpose mode of the computer 3. The same functions have been made so that they can be selected arbitrarily. An external video signal input from an external video device and an RGB signal input from the computer 3 are input to the screen composition processing circuit 4. Also,
When CPU mode is selected, two types of synchronization modes can be selected: external synchronization mode and internal synchronization mode. External sync mode is a mode (interlace mode) that outputs RGB signals synchronized with the input external video signal, and internal sync mode is a mode that outputs RGB signals that are synchronized with the input external video signal. Internal sync mode is the mode that outputs RGB signals that are synchronized with the input external video signal. This is a mode (non-interlace mode) in which synchronization is achieved and output is achieved using a synchronization signal or a burst signal. These synchronous modes are switched as appropriate by a changeover switch 5.
A change-over switch signal 6 indicating the state of the change-over switch 5 controls a synchronization changeover circuit 7 (consisting of an IC) to select internal synchronization 8 or external synchronization 9 and output it to the screen composition processing circuit 4. It is being output. That is, the vertical synchronization pulse V _SYNC output from the computer 3 with internal synchronization 8 selected,
The horizontal synchronizing pulse H _SYNC becomes the internal synchronizing signal, and the horizontal synchronizing pulse H _SYNC becomes the phase comparator circuit 10.
(configured by IC). This phase comparison circuit 10 has a frequency of 3.58MHz (to be exact,
3579.545kHz) The signal output from the oscillator 11 is divided by 1/244 by the frequency divider 12 to create a 15.98kHz horizontal synchronization pulse, and this horizontal synchronization pulse and the horizontal synchronization pulse output from the computer 3
A phase detector provided in the phase comparison circuit 10 compares the phase of H _SYNC and outputs a burst signal (non-interlaced burst). This burst signal is generated in accordance with the phase of the RGB signal from the computer 3, and is input to the synchronization switching circuit 7. On the other hand, if external synchronization mode is selected,
Interlace burst circuit 16 from external video signal
The burst signal is extracted by
External synchronization signals are taken out, each input to the synchronization switching circuit 7, and supplied to the screen synthesis processing circuit 4. The horizontal synchronizing signal HD output from the monitor television 2 is connected to the changeover switch signal line 6 via a mode detection circuit 13. A specific circuit of this mode detection circuit 13 is shown in FIG. In FIG. 2, the horizontal synchronizing signal HD is passed through an AND gate 14 and an integrating circuit 15 to a transistor
The switching operation of _the transistor _Q1 causes the switching state of the changeover switch signal 6 to be in the external synchronization mode. The other input terminal of the AND gate 14 is held at the "H" level, and the integrating circuit 15 is connected by a capacitor C ₁ and resistors R ₁ and R ₂ to accelerate the rise, and is connected to the integrator circuit 15 through a diode D ₁ . The capacitor _C2 is charged with an integral amount obtained by integrating the "H" level of the horizontal synchronizing signal HD. And resistance
The bias value of transistor Q ₁ is set appropriately by R ₃ and R ₄ . In the video conversion device 1 having the above configuration, when the computer 3 is in the CPU mode, an RGB signal synchronized with the vertical synchronization pulse V _SYNC and the horizontal synchronization pulse H _SYNC is supplied to the monitor television 2 together with these synchronization pulses. There is. The monitor television 2 displays RGB signals on the screen in synchronization with these synchronization pulses. The horizontal synchronization pulse H _SYNC at this time is, for example, 15.98kHz,
The horizontal frequency determined by the NTSC signal
It rarely matches 15.734kHz, and similarly the vertical synchronization pulse V _SYNC rarely matches the frequency determined by the NTSC signal. This is because of the relationship between the display areas of the RGB signals on the monitor television 2 and the fact that it is not necessary to display the video signals on the same screen. On the other hand, when computer 3 is set to superimpose mode, the RGB signals output from computer 3 must be output in synchronization with the NTSC signal, so
The horizontal synchronization signal HD and vertical synchronization signal VD are supplied to the computer 3 in accordance with the synchronization signal of the NTSC signal. Then, the computer 3 synchronizes with this horizontal synchronization signal HD and vertical synchronization signal VD,
Outputs RGB signals and displays video signals and RGB signals on the same screen. Therefore, when the computer 3 is in a mode other than the superimpose mode, this mode detection circuit 13
Since the horizontal synchronization signal HD is not outputted, the transistor _Q1 is cut off, and switching between external synchronization and internal synchronization can be performed by the changeover switch 5. On the other hand, when the computer 3 enters the superimpose mode, the monitor television 2 outputs a horizontal synchronizing signal HD. Therefore, the horizontal synchronizing signal HD is also input to the mode detection circuit 13, passes through the integrating circuit 15, makes the transistor _Q1 conductive, and the changeover switch signal line 6 becomes "L" level regardless of the switching state of the changeover switch 5. Automatically enters external synchronization mode. Table 1 below shows synchronization methods when modes other than those described above are selected.

[Table] (Effects of the Invention) The video conversion device of the present invention provides the video conversion device that supplies the video from the monitor TV to the computer when superimpose is selected by the computer.
The configuration is equipped with a mode detection circuit that detects the horizontal synchronization signal of the NTSC signal and switches to external synchronization mode regardless of the switching state of the switch, so the computer can synchronize in CPU mode and the video converter can synchronize in CPU mode. Even if you switch the computer to superimpose mode while it is selected, external synchronization will be automatically selected.
The user does not have to take the trouble to change the switch, and can enjoy images without color synchronization disturbance.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of a video conversion device according to the present invention, and FIG. 2 is a circuit diagram showing a specific configuration of a mode detection circuit. 1...Video conversion device, 2...Monitor TV, 3...
Computer, 6...Switch signal line, 13...
Mode detection circuit, 15...integrator circuit.

Claims (1)

[Claims] 1. A device intervening in a system that has at least a superimpose function that superimposes a video signal and an RGB signal from a computer and displays the superimposed image on a monitor TV screen, and which has a mode in which only the RGB signal is displayed on the screen and an external device. It has a mode in which only the external video signal input from the video equipment is displayed on the screen, and a mode in which those RGB signals and the external video signal are superimposed, and the RGB signal output from the computer is synchronized with the external video signal. A changeover switch is provided for switching between an external synchronization mode in which the signal is output in synchronization with the synchronization signal and the burst signal generated within the device, and an internal synchronization mode in which the output is performed in synchronization with the synchronization signal and burst signal generated within the device. Sometimes supplied from the monitor TV side to the computer side
A video conversion device comprising a mode detection circuit that switches to an external synchronization mode by detecting a horizontal synchronization signal of an NTSC signal, regardless of the switching state of the changeover switch.