JPH01141474A - Display control circuit in television receiver - Google Patents

Abstract

PURPOSE:To display a on-screen character in the prescribed position on a CRT screen by counting the number of the horizontal pulses of respective fields and correcting the output timing of the on-screen character when the prescribed number of pulses is changed. CONSTITUTION:A difference between the number of the horizontal pulses (=346) in 1 field period at the time of the signalless and the number of the horizontal pulses in 1 field period at the time of receiving a broadcasting signal, namely, the prescribed number of the pulses (=312) is obtained (346-312=34), a vertical amplitude at the time of the signalless is equally enlarged up and down, the difference is made into 1/2 (34divided by 2=17), it is made into a correcting portion, it is added to an initial value (=30), and the initial value is corrected to 47(=30+17). The corrected initial value is given to a vertical direction control register 4, the output timing of the on-screen character is corrected in the next field, and thus, an on-screen displaying position is made into a fixed position on the CRT screen.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a display control circuit for a television receiver, and more particularly to correction of display position in on-screen display of volume, channel, etc.

<Prior art> In recent years, television receivers have been equipped with various controls such as channel, volume, input switching, etc., so that various operations can be checked from a distance as remote control functions have been enhanced. A so-called on-screen function has been added.

This on-screen function determines the on-screen display position for the image using horizontal and vertical pulses inside the TV set.The counter is reset with the vertical pulse, and then the number of horizontal pulses is counted and the preset When the specified initial value is reached, an on-screen signal is output and an on-screen display is performed.

By the way, in television receivers, when there is no signal, such as when selecting an empty channel or when there is no signal, such as in an unmanned state during AV, the frequency becomes a free run frequency determined by the circuit system of the television receiver. Since the vertical oscillation frequency becomes lower, the pp value of the vertical deflection current increases, the raster size becomes larger, and the number of horizontal pulses also increases.

Therefore, conventional television receivers that count the number of horizontal pulses and output an on-screen signal when the counted value reaches a preset initial value are useless. When receiving a signal, the on-screen display position moves upward compared to when receiving a broadcast signal, and some of the on-screen characters displayed at the corners of the CR1 screen may protrude from the screen and be missing.

FIG. 6 is a diagram of the CR1 screen showing this display position shift, with arrows A1. A2 indicates the position of the raster edge when there is no signal and when receiving a broadcast signal, and the arrow Bl
, B2 indicate the output start points of on-screen characters when there is no signal and when a broadcast signal is received, respectively. Further, a rectangular area Ct surrounded by a broken line and a rectangular area C2 surrounded by a solid line indicate on-screen character display areas when there is no signal and when a broadcast signal is received, respectively.

7 and 8 respectively show vertical and horizontal pulses when receiving a broadcast signal and when there is no signal corresponding to FIG. 6. Conventionally, regardless of when a broadcast signal is received or when there is no signal, a counter is reset with a vertical pulse and horizontal pulses are counted, and when the counted value reaches a preset initial value, that is, as shown in FIG. Since the on-screen characters are output at the timing t shown in FIG. 8, the display position will be shifted as shown by CI and C2 in FIG. 6.

Such a shift in the on-screen display position is particularly noticeable in systems with a vertical frequency of 50 Hz.For this reason, it is possible to display on-screen characters closer to the center of the CR1 screen, but the original image This is not desirable as it will interfere with the operation.

<Object of the Invention> The present invention has been made in view of the above-mentioned points, and it is possible to display on-screen characters at a fixed position on the CR1 screen regardless of whether a broadcast signal is received or no signal is received. The purpose is to

<Structure of the Invention> In order to achieve the above-mentioned object, the present invention starts counting horizontal pulses in response to vertical pulses, and when the counted value reaches a preset initial value, an on-screen A display control circuit in a television receiver that outputs signals for on-screen display, and includes a counting means for counting the number of horizontal pulses in each field, and an on-screen display on the screen based on the output of this counting means. A correction means is provided for correcting the initial value when the number of horizontal pulses in each field changes from a predetermined number of pulses so that the display position is constant.

According to the above configuration, when the number of horizontal pulses in the l-field period changes from a broadcast signal reception state to a no-signal state, the initial value is corrected according to the change, and the output timing of on-screen characters is adjusted. This will cause the on-screen characters to always be displayed at a fixed position on the CRT screen.

<Examples> Examples of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a block diagram of essential parts of an embodiment of the present invention.

In the figure, ■ is a display on/off control circuit that controls on-off of the on-screen display, 2 is a data latch circuit that latches data from the data bus, 3 is a character size control register that holds character size data, and 4 is a vertical direction 5 is a vertical direction control register that holds data corresponding to the on-screen display position; 5 is a display position control circuit that controls the display position of on-screen characters based on the horizontal and vertical pulses and the set value of the control register 4; Display clock generation circuit, 7 is the character R in which display characters are stored.
OM (character generator); 8 is a display RAM that temporarily stores the address data of the character ROM; 9 is a display color control circuit that controls the color of on-screen characters; 10 is R;
A display output control circuit 2 is a register which outputs G and H character signals for the screen as well as a blanking signal for switching between a television video signal and an on-screen character signal.

The above is basically the same configuration as the on-screen function of the conventional example. Counting of horizontal pulses is started in response to vertical pulses, and the counted value is set to the initial value set in the vertical control register 4. When this happens, the display output control circuit 10 outputs an on-screen character signal to perform on-screen display.

This initial value is the same as before when the CRT
On-screen characters are set in advance to be displayed at a certain position on the screen.

In the display control circuit of the television receiver of this embodiment,
To prevent on-screen characters from protruding from the CRT screen due to the raster size increasing when selecting an empty channel or when there is no signal such as when AV is unattended, the following configuration is used. There is.

That is, a pulse counter 12 is provided to count the horizontal pulses of each field, and based on the output of this pulse counter 12, when the number of horizontal pulses in the l field period changes from a predetermined number of pulses corresponding to the reception of the broadcast signal, , In accordance with the change, the arithmetic unit (ALU) 13 serving as a correction means performs a predetermined calculation described later to correct the initial value, and sets it in the vertical direction control register 4 to output on-screen characters in the next field. I'm trying to correct the timing.

Next, regarding correction of the on-screen display position, see Figure 2~
This will be explained based on FIG.

FIG. 2 is a diagram showing the CRT screen of this embodiment, and FIGS. 3 to 5 show the vertical and horizontal pulses of three consecutive fields, respectively.

FIG. 3 corresponds to when a broadcast signal is received, and FIGS. 4 and 5 correspond to when there is no signal.

In FIG. 2, arrows A l and A 2 indicate the raster edge positions when there is no signal and when receiving a broadcast signal, respectively, and arrow Bl indicates the position of the raster edge when there is no signal and when the correction according to the present invention is applied. The arrow B2 indicates the output start point of on-screen characters in the previous field, and the arrow B2 indicates the output start point of on-screen characters after correction when there is no signal or when a broadcast signal is received. Further, a rectangular area C indicates an on-screen display area.

In this example, the vertical and horizontal frequencies are 50Hz.

This will be explained by applying it to a 15.625kHz method.

First, in the vertical direction control register 4, when receiving a broadcast signal,
That is, the number of horizontal pulses in one field period is 312.
(Actually, it is 312.5, but since 0.5 cannot be counted), the initial value is set so that on-screen characters are displayed at a certain position on the CRT screen.
30 is set.

In the broadcast signal reception state shown in FIG. 3, the output of the pulse counter 12 is 312, which is the predetermined number of horizontal pulses, so it is displayed on-screen as before without correcting the initial value. .

Next, when the no-signal state shown in FIG. 4 is reached, the number of horizontal pulses in the l-field period increases, and for example, if the output of the pulse counter 12 becomes 346, the arithmetic circuit 13 calculates the following: to correct. Note that the vertical pulse width corresponds to the vertical retrace period, and the horizontal pulse that exists during this period is originally corrected by subtracting it, but here,
This will be ignored for the sake of brevity.

Number of horizontal pulses in one field period when there is no signal (=
3413) and the number of horizontal pulses in one field period when receiving a broadcast signal, that is, the predetermined number of pulses (=31
2) (346-312=34), assuming that the vertical amplitude when there is no signal is expanded evenly above and below, and dividing this difference by 1/
2 (34÷2=17), and this is added to the initial value (=30) as a correction amount to correct the initial value to 47 (=30+17).

This corrected initial value is given to the vertical direction control register 4, and in the next field, the output timing of on-screen characters is corrected as shown in FIG. In this case, the on-screen display position is a fixed position on the CRT screen.

In addition, in FIGS. 3 to 5, the output timing of on-screen characters is indicated by T.

In this way, the number of horizontal pulses in each field is counted, and when the number of horizontal pulses increases, such as when the state changes from receiving a broadcast signal to no signal, the output timing of on-screen characters is corrected according to the change. Therefore, the on-screen characters are always displayed at a fixed position on the CRT screen, and there is no possibility that the on-screen characters are missing as in the conventional example.

<Effects of the Invention> As described above, according to the present invention, the number of horizontal pulses in each field is counted, and when the number of horizontal pulses changes from a predetermined number,
Since the output timing of on-screen characters is corrected, regardless of whether there is a broadcast signal received or no signal,
On-screen characters can be displayed at a fixed position on the CRT screen.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of one embodiment of the present invention, and FIG. 2 is a block diagram of an embodiment of the present invention.
Figures 3 to 5 are waveform diagrams showing vertical and horizontal pulses, respectively. Figure 6 is a diagram showing the CRT screen of the conventional example. Figures 7 and 8 are FIG. 3 is a waveform diagram showing vertical and horizontal pulses, respectively. 12...Pulse counter! 3... Arithmetic circuit (correction means).

Claims (1)

[Claims] (1) A television receiver that starts counting horizontal pulses in response to vertical pulses and outputs an on-screen signal to display on-screen display when the counted value reaches a preset initial value. A display control circuit comprising: a counting means for counting the number of horizontal pulses in each field; and a counting means for counting the number of horizontal pulses in each field so that the on-screen display position on the screen is constant based on the output of the counting means. 1. A display control circuit for a television receiver, comprising: correction means for correcting the initial value when the number of pulses changes from a predetermined number of pulses.