JPH03267995A - Sign display device - Google Patents

Abstract

PURPOSE:To display a sign at an invariably constant position by providing a vertical correcting means which generates a vertical synchronizing signal shifted in phase according to a vertical and a horizontal synchronizing signal and a horizontal correcting means which varies the synchronism of a timing signal according to the horizontal synchronizing signal. CONSTITUTION:The vertical correcting means 1 counts pulses of the horizontal synchronizing signal in one cycle of the vertical synchronizing signal to detect the number of scanning lines and calculates the generation position of a vertical display start pulse for displaying the sign at the specific position on a screen in the vertical direction by proportional calculation. The difference between this position and a reference position which is predetermined as to the standard number of scanning lines, the vertical synchronizing signal is shifted in phase by pulses of the horizontal synchronizing signal as many as the difference, and the sign is displayed at the vertically same position. The horizontal correcting means 6 corrects the period of the timing signal used in the sign display device according to the period of the horizontal synchronizing signal to hold the horizontal position and size of the sign equal. Consequently, the sign can be displayed on the screen at the same position to the same size.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention is used in a video display device that can handle multiple video signals (television signals) with different horizontal scanning frequencies and numbers of scanning lines, and is used for superimposing video signals on normal video. The present invention relates to a sign display device for displaying signs such as characters and symbols on a screen.

2. Description of the Related Art An LSI generally called a CRTC is used to generate digital signs such as characters and symbols on television receivers and the like. As shown in Figure 2, it receives an external vertical synchronizing signal (normally a vertical blanking pulse is used) and a horizontal synchronizing signal (also a horizontal blanking pulse is used), and combines these synchronizing signals with the internal The clock 7 is used to output a sign display signal (digital sign signal) so that a sign is displayed at a predetermined position on the screen.

The CRTC 6 generates a sign display signal as follows. First, as shown in FIG. 3(a), the vertical display is started in order to start the sign display after a predetermined number of scanning lines (in the example in the figure, m lines = m - H) using the vertical synchronization signal as a reference. Generate pulses internally. This determines the vertical position of the sign on the screen. From the time when this vertical display start pulse is issued, as shown in FIG. 3(b), after a predetermined clock cycle (n clock cycles in the figure) from each horizontal synchronizing signal, the signal for sign display is transmitted for a predetermined clock cycle. (in the figure, it is output only for 2 clock cycles). This determines the position and size of the sign in the horizontal direction of the screen. The CRTC 6 is equipped with an external coil L and capacitor C so that the oscillation frequency of the built-in clock 7 can be changed externally.
A terminal for connecting the clock 7 to the clock 7 is provided.

Video signals with different horizontal scanning frequencies and numbers of scanning lines can be
When entering the RTC6, in this method of generating a sign display signal based on each synchronization signal, synchronization with the deflection system can be achieved, so although the sign is displayed on the screen, the display position and The size will change. In extreme cases, a problem arises in which a part of the signature is missing, making the signature difficult to read.

An object of the present invention is to solve such problems and provide a sign display device that can always display a sign at a constant position even for video signals with different horizontal scanning frequencies and numbers of scanning lines. .

Means for Solving the Problems In order to achieve the above object, the present invention provides a sign display system that receives a vertical synchronization signal and a horizontal synchronization signal of a video signal and generates a sign display signal based on an internally generated timing signal. In the display device, vertical correction means for generating a phase-changed vertical synchronization signal based on the vertical synchronization signal and the horizontal synchronization signal, and horizontal correction means for changing the cycle of the timing signal based on the horizontal synchronization signal. It is characterized by having the following.

Note that the vertical synchronization signal or horizontal synchronization signal here is
Any signal synchronized with the sweep in each direction may be used.

Operation The vertical correction means detects the number of Shiba scan lines by counting the number of horizontal synchronization signals in one cycle of the vertical synchronization signal. This allows the lever to be used at the generation position m of the vertical display start pulse for displaying a sign at a predetermined position in the vertical direction on the screen (i.e., the vertical display start pulse is generated at the m-th horizontal synchronization signal after the vertical synchronization signal). ) is calculated by proportional calculation.

This position m and a reference position m that is predetermined regarding the standard number of scanning lines. What difference is taken, and the phase of the vertical synchronization signal is shifted by the number of horizontal synchronization signals equal to the difference (mm). This ensures that the sign is always displayed at the same vertical position on the screen.

The horizontal correction means corrects the period of the timing signal used inside the sign display device based on the period of the horizontal synchronization signal. This allows the horizontal position and size of the sign to always be kept the same.

Example.

In FIG. 1, a sign display correction circuit 1 is provided outside the CRTC-LSIS to correct the vertical blanking pulse b and horizontal blanking pulse a input to the CRTC 6. The sign display correction circuit 1 includes a frequency comparator 2, an oscillation frequency controller 3 that controls the oscillation frequency of the display clock 7 of the CRTC 8, a frequency divider 4 that divides the frequency of the display clock signal of the CRTC 6, and a vertical blanking pulse b. It consists of a phase controller 5 that controls the phase of. Frequency comparator 2
The oscillation frequency controller 3, the clock 7 built into the CRTC 6, and the frequency divider 4 are connected to form a loop, and the phase controller 5 is connected to the vertical blanking pulse input terminal 8 of the CRTC 6. Horizontal blanking pulse a is directly CRTC
6 is input to the same pulse input terminal 9.

The operation of this display correction circuit 1 is as follows.

Frequency comparator 2 has horizontal blanking pulse a and frequency divider 4
, and outputs a control signal d according to the difference in frequency between the two. The control signal d is the oscillation frequency controller 3
is input to CR so that the difference in frequency between the two becomes small
Controls the oscillation frequency of the TC built-in clock 7. Frequency divider 4
receives the oscillation signal e of the built-in clock 7 and divides the frequency to a frequency that can be easily compared with the horizontal planking pulse a. That is, this loop constitutes a kind of frequency negative feedback circuit, and operates so that the oscillation frequency of the clock 7 is always a predetermined times the frequency of the horizontal blanking pulse (multiple the division ratio of the divider 4).

The horizontal blanking pulse a and the vertical blanking pulse b are input to the phase controller 5, and the number of pulses of the horizontal blanking pulse a during one period of the vertical blanking pulse b is counted, and this number of pulses is The phase of the vertical blanking pulse b is shifted accordingly. That is,
If the number of pulses is less than a predetermined standard value (for example, 262), the phase of the vertical blanking pulse is advanced; if it is more, it is delayed. This phase-shifted vertical blanking signal f is input to terminal 8 of CR, TC6. The horizontal blanking pulse a is input as is to the terminal 9 as described above.

The CRTC 6 creates a digital sign signal g for displaying a sign such as a character given from the outside based on the horizontal blanking pulse a and the corrected vertical blanking pulse f. At this time, since the clock cycle of the built-in clock 7 corresponds to the horizontal scanning frequency, the horizontal position and size of the sign are always kept constant even if the horizontal scanning frequency of the television signal changes. It will be done. Furthermore, since the phase of the vertical blanking pulse f has already been appropriately corrected by the correction circuit 1, the position of the sign from the top of the screen is always constant. The digital sign signal g generated in this way is mixed with a normal video signal by a mixing IC (not shown), and the CRT
is output to.

In the above embodiment, the sign display correction circuit 1 is a CRTC
6, but of course it can also be incorporated in advance as part of the sign display device.

Detailed Description of the Invention According to the present invention, a VDT for a television receiver or a personal computer that supports a plurality of horizontal scanning frequencies is provided.
etc., signs such as letters and symbols can always be displayed in the same position and size on the screen. This prevents the sign from being chipped and improves visibility.

Figure 2

[Brief explanation of drawings]

Fig. 1 is a circuit diagram of an embodiment of the present invention in which a sign display correction circuit is provided outside the CRTC, Fig. 2 is a schematic diagram of the CRTC-LSI connection for sign display, and Fig. 3 (a) and (b) are timing charts explaining the timing of digital sign signal generation in CRTC. Figure 3

Claims (1)

[Claims] (1) In a sign display device that receives a vertical synchronization signal and a horizontal synchronization signal of a video signal and generates a sign display signal based on an internally generated timing signal, based on the vertical synchronization signal and horizontal synchronization signal, A sign display device comprising: vertical correction means for generating a vertical synchronization signal whose phase has been changed; and horizontal correction means for changing the period of the timing signal based on the horizontal synchronization signal.