JPH0213796B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a color video display control circuit for displaying, for example, digital data from a personal computer in dots on a general color television receiver. In recent years, with the spread of personal computers and microcomputers, general household television receivers have become widely used as monitor devices for displaying data.In this case, digital data signals from computers are displayed on a dot display. A video display control circuit is required to convert the video signal into a type of video signal. When converting this digital signal into a dot display video signal, it is necessary to determine in advance the dot clock frequency _dpt for displaying each dot. The above _dpt was determined depending on the situation. In other words, it depends on how many dots of dot matrix one character (letters, numbers, symbols, etc.) is displayed, and how many lines and digits of characters are displayed on one screen.
The above _dpt was determined almost uniquely. By the way, when displaying video based on _{the dpt} selected in this way, there is almost no problem with monochrome images (so-called black and white images), but when displaying color images, the color subcarrier frequency _sc and the above _dpt are Due to the relationship between There are drawbacks such as the possibility of misidentification. Here, it has been considered to provide an oscillator for obtaining the above _dpt separately from the reference oscillator for obtaining the above _sc , and to shift the oscillation frequencies of these oscillators to reduce the adverse effects of the above mutual interference. , since two oscillators are required, the circuit configuration becomes complicated and expensive, and each oscillator is independently influenced by temperature changes and the frequency fluctuates, so horizontal and vertical deviations of each dot, etc. A circuit is required to compensate for the
Compared to those that form _SC or _DPT , the circuit configuration is more complex and adjustment is difficult. The present invention has been made in view of such conventional circumstances, and it is possible to obtain the color subcarrier frequency _sc and the dot clock frequency _dpt by dividing the oscillation frequency from one reference oscillator, and further, The object of the present invention is to provide a color video display control circuit that does not cause defects such as color shift or color unevenness in each display dot. That is, the feature of the color video display control circuit according to the present invention is that in the color video display control circuit that converts digital dot display data into a standard color television video signal and displays a color video on a CRT, the color subcarrier frequency is _sc , the horizontal scanning frequency is _H , and the dot clock frequency of display dots is _dpt , then _dpt = n/m _{sc dpt} = l _H , where l, m, and n satisfy the relationship of integers, and are integral parts of the above _dpt . The above _value is set so that the frequency value of 1 of
The key is to select _dpt . Preferred embodiments of the present invention will be described below. First, set the highest reference frequency of the color video display control circuit system to n times the color subcarrier frequency _sc (n
= 1, 2, 3,...), and this highest reference frequency
The above _sc is obtained by dividing _sc by n, and the above sc is also divided by m (m=
1, 2, 3,...) and the dot clock frequency _dpt
I am getting . Therefore, it is necessary to satisfy the following relational expression: _dpt = n/m _sc . next,
Each dot must be arranged vertically on the screen, and one dot on the screen and the dot immediately above (or below) it are equal to one horizontal scanning period (IH period).
Since the images are displayed with a timing difference of _dpt = l _{H .} . . , where l = 1, 2, 3, . Furthermore, the above _dpt is the above _sc
, for example, within the range of _sc ±Δ _sc , mutual interference occurs between these _dpt and _sc , causing problems such as coloring of white dots. Furthermore, for example, when displaying (lighting up) and non-displaying (turning off) every 2 dots, 1/2
It is necessary that _dpt does not fall within the above range of _sc ±△ _sc , and 1/3 _dpt is...
Therefore, it is generally necessary to prevent 1/k _dpt (k=1, 2, 3, . . . ) from falling within the range of _sc ±Δ _sc . Here, in the standard color television signal of the NTSC system, the above _sc is approximately 3.58MHz, and the above △ _sc is, for example, 0.5M
It may be about Hz. At this time, the frequency bands that can be used as _dpt are shown in Table 1.

[Table] 5 15.40～20.40...
… …
As is clear from Table 1, the frequency bands that can actually be used are 4.08~6.16 (MHz), 8.16~
There are only three bands: 9.24 (MHz) and 12.24 to 12.32 (MHz), and within this band, the above,
It is sufficient to select _{a dpt} that satisfies the conditional expression, and provide a reference oscillator whose highest reference frequency is m _dpt based on this _dpt . By the way, when displaying characters such as letters, numbers, and symbols on the screen, the number of dots that make up these characters becomes a problem.In particular, when the number of dots in the horizontal direction is d, the number of dots on one line is a problem. The value obtained by dividing (the above l) by this d becomes the number of characters (number of digits) arranged in the horizontal direction. Therefore, when the character clock frequency is _c , d _c = _dpt ... Also, when the above number of digits is c, _c = c _H ... However, c, d = 1, 2, 3,... It is desired that the following relational expression be satisfied. Specific numerical examples of each frequency in the NTSC system will be explained under these formulas and the conditions shown in Table 1 above. First, the above _sc and _H have the following relationship: _sc = 455/2 _H = 5・7・13/2 _H ... Using this formula and the above formula, _dpt = 5・7・13・n/2・m _H …… The formula is obtained. In order for the coefficient term of _H in this equation to be an integer, n must be an even number and m must be a factor of 5, 7, 13, or n/2. Furthermore, by substituting this equation into the above equation, it is necessary to satisfy the following equation: _c = 5.7.13.n/2.d.m _H . Here, for example, 6 or 8 is selected as the number d of dots in the horizontal direction per character, and the number of characters (number of digits) arranged on the screen in the horizontal direction is, for example, 40 digits or 80 digits. When choosing the above _dpt
The values of are shown in Table 2.

[Table] The shaded areas in Table 2 indicate that m is 5,
7, 13, or n/2 factors, and even if this condition is satisfied, the first
Only the six underlined frequency values in Table 2 satisfy the conditions in the table. Furthermore, in order to be able to switch the number of characters in the horizontal direction of the screen between low and high density display, such as 40 digits and 80 digits, in the case of 1 character and 6 dots, 6.14 MHz and 12.27 MHz are required.
In the case of a set of Hz and 8 dots per character,
You can select a pair of 4.41MHz and 8.81MHz. Here, FIG. 1 shows that each frequency _sc , _dpt , _c , _H , etc. is determined using one reference oscillator 1 whose reference oscillation frequency is m _dpt based on the dot clock frequency _dpt selected as described above. An example of a circuit configuration for obtaining the above is shown below. In FIG. 1, the oscillation frequency m _dpt of the output signal from the reference oscillator 1 is divided by 1/m by the frequency divider 2 to obtain the dot clock frequency _dpt , which is then divided by 1/d by the frequency divider 3. As a result, the character clock frequency _c is obtained. Also, since the above m _dpt is n _c , n'=n/
2, the frequency divider 4 divides it by 1/n' (=2/n),
Further, by dividing the frequency by 1/2 using a frequency divider 5, a color subcarrier frequency _sc is obtained. Further, by dividing the output from the frequency divider 4 by 1/455 by the frequency divider 6, the horizontal scanning frequency _H is obtained. For example, if _{the dpt} in Table 2 is 12.27MHz, the reference frequency of reference oscillator 1 is 85.91MHz,
The frequency can be divided by 1/7 using frequency divider 2. At this time, n
= 24, so n' = 12, and the above reference frequency
85.91MHz is finally 1/24 by frequency divider 4 and 5
As a result, _{an SC} of approximately 3.58 MHz is obtained, and _{an H} signal of approximately 15.7 kHz is obtained by frequency dividers 4 and 6. At this time, the number d of dots in the horizontal direction of one character is 6.
, approximately 80 characters (80 digits) can be displayed in the horizontal direction, but if you want to switch to 40 character display, use the reference oscillator 1 as shown in Figure 1.
A changeover switch 7 and a frequency divider 8 are inserted and connected between the changeover switch 7 and the frequency divider 2, and by switching the changeover terminal of the changeover switch 7 from a to b, the output from the reference oscillator 1 is transferred to the frequency divider 8. to 1/2, divider 2
I am sending it to In this case, the frequency of the input signal to frequency divider 2 is 42.95MHz, which is divided by 1/7.
It has _{a DPT} of 6.14MHz and can display 40 characters. By the way, the effective display area in one screen is about 40 μsec within 1H period (about 63.5 μsec). For example, when one character consists of 6 dots in the horizontal direction and this character is displayed in 40 digits horizontally, the time required for display T _D is expressed as T _D = 40 x 6 x 1/ _dpt ... When _dpt is 6.14MHz, T _D in the above equation is approximately 39.1 μsec, which can be conveniently displayed in the effective display area on the screen. Regarding other _dpt ,
The number of digits that can be displayed exactly in the effective display area is determined. As is clear from the above description, according to the color video display control circuit according to the present invention, by dividing the highest reference frequency from one reference oscillator by m, the dot clock frequency _dpt is also divided by n. By doing this, the color subcarrier frequency _sc is obtained, and each frequency _H , _V of the video synchronization signal is
etc. can also be obtained by frequency division. Also, the above _dpt obtained in this way is the above _sc
Since it satisfies the condition that no mutual interference occurs with the screen, it is possible to prevent adverse effects such as color shift and color unevenness of dots on the screen, and it is possible to monitor with good image quality.
Furthermore, the dots are arranged in a straight line in the vertical direction, so their positions do not move, and characters can be displayed effectively.

[Brief explanation of drawings]

FIG. 1 is a block circuit diagram showing an example of a frequency dividing circuit system for each frequency signal as a main part of an embodiment of the present invention. 1...Reference oscillator, 2, 3, 4, 5, 6, 8...
... Frequency divider, 7... Selector switch.

Claims (1)

[Scope of Claims] 1. A color video display control circuit that converts digital dot display data into a standard color television video signal to display a color video on a CRT,
The color subcarrier frequency is _sc , the horizontal scanning frequency is _H , and the dot lock frequency of display dots _{is dpt.}
When, _dpt = n/m _{sc dpt} = l _H However, l, m, and n satisfy the relationship of integers, and the frequency value of 1/integer of the above _dpt does not fall within the above _sc neighborhood range. the above
A color video display control circuit characterized by selecting _dpt .