JPH09271001A - Method for controlling character code for character broadcasting and signal processing circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a character display procedure capable of reducing memory capacity and attaining smooth scrolling without increasing the memory capacity. SOLUTION: In the case of outputting a displaying character code, the data of a 2nd character are read out by the timing of a 1st character of each line to determine and output the character code of the 1st character and the character code of a final character is determined from the data of a character just before the final character and outputted at the timing of the final character. In the case of a closed caption, its signal processing circuit is constituted of a comparator 1 for comparing data from a memory with a blanking code (20h) and a transparent code (00h), a 1st switch 3a for selecting the transparent or blanking code in accordance with outputs (EQU, EQUA) from the comparator 1 and a 2nd switch 3d for outputting the code selected by the 1st switch 3a at the timing of 1st and 34th characters and outputting and transmitting read data at the output timing of the 2nd to 33th characters. Since the memory capacity for the 1st and the last characters of each line can be omitted, the memory capacity can be made to be just 512 bytes even when the capacity equivalent to one line is added for the purpose of making scrolling smooth.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a signal processing circuit that can be used for displaying characters such as alphabets and figures in character broadcasting such as closed caption system.

[0002]

2. Description of the Related Art In the closed caption system, which is a typical teletext broadcasting, the specification of 34 characters × 15 lines is set for the text display on the display device. Therefore, a typical on-screen display (OSD) device requires at least a memory capacity of 34 × 15 = 510 bytes.

[0003]

[Problems to be Solved by the Invention] 5 of 34 characters x 15 lines
When an OSD device having a 10-byte capacity is used, scrolling is realized by sequentially rewriting display information. In this case, the larger the memory capacity, the heavier the load on the CPU. In addition, if smooth scrolling is to be performed, an additional capacity for one line is required, which cannot be performed in the 512-byte memory space. They are,
It is also one of the factors that make it difficult to make OSD into a one-chip microcomputer.

In view of these problems to be solved, the present invention provides:
A method for displaying characters in a character broadcast which requires less memory capacity. It also provides a method for displaying characters in a character broadcast that enables smooth scrolling without increasing the existing memory capacity.

[0005]

In the closed caption system, for example, the substantial character display area of 34 characters × 15 lines is 32 characters × 15 lines, and the first character of each line and the 34th character which is the last character Is always a blanking character or a transparent character (transparent character that allows TV images to be seen) for scrolling or the like. That is, in the text mode in which the entire screen is used for displaying characters, the first character and the 34th character are always character codes of blanking characters, and a part of the screen is used for displaying characters to display the TV image and the characters at the same time. Then, according to the code of the second character and the code of the 33rd character, which is the character before the final character, the character code is determined whether the 1st character and the 34th character are blanking characters or transparent characters. As described above, the first character and the 34th character are only blanking characters or transparent characters.

In view of this point, the memory capacity for the actual display character is sufficient to be 32 characters × 15 lines = 480 bytes, so that the first character and the last character of each line can be saved without using the memory. If possible, at least 480
It only needs to have a memory capacity of bytes. In addition, in this case, 512 bytes are enough even if one line is added in order to perform wraparound display for smooth scrolling by connecting upper and lower character portions by vertical scrolling.

Therefore, according to the present invention, as a character code control method for outputting a character code of a display character for displaying a teletext, the data of the second character is read out at the timing of the first character of each line and is read from the data. A character code control method for determining and outputting the character code of the first character, and a character code control method for determining the character code of the last character from the data of the character before the last character of each line and outputting at the timing of the last character, and
A character code control method that combines these two methods is provided. Thus, if the character code of the first character is generated from the data of the second character, or the character code of the last character is generated from the data of the character immediately before the last character, the first character or the last character is generated. Since the memory capacity for characters can be omitted, the closed caption method can have a memory capacity of 33 characters x 15 lines. Or a control method that combines both, that is,
The data of the second character is read at the timing of the first character of each line, the character code of the first character is determined and output from the data, and the character code of the last character is determined from the data of the character before the last character of each line. If it is a character code control method that outputs at the timing of the last character,
With a memory capacity of 32 characters x 15 lines, it is possible to support closed caption system character broadcasting. Moreover, according to this, even if the capacity for one line is added to perform the wraparound display, 512 bytes are required.

According to the present invention, as a signal processing circuit suitable for such a character code control method, a comparator for comparing whether character data read from a memory matches a specific character code and a predetermined value according to the output of the comparator. And a character code selected from the character code and output at the timing of the first character and / or the last character, and the character data read from the memory is transmitted and output at the timing of the character other than the first character and / or the last character. And a signal processing circuit comprising:

That is, first, the memory in this case is the second character
Since only the character before the last character is stored, the character data of the second character is first read and input to the comparator, and is it the code of the displayed character such as alphabet, or a specific character code of the blanking code or the transparent code? Is determined. According to the result of this determination, if the switch is a display character code (mismatch), a blanking code, and if it is a specific character code (match)
A predetermined character code, such as a transparent code, is selected. Then, the selected character code is output at the character code output timing of the first character, and thereafter, the character data of the second and subsequent characters read from the memory is continuously transmitted and output. In the memory access at this time, the CPU may control the data of the second character first and maintain the data for the second reading. However, since an extra circuit such as a data holding circuit is required, It is preferable to read the data of the second character twice in succession.

In the case of the character code generation output of the final character, the data of the character before the final character is compared with the specific character code by the comparator, so that the predetermined character code is selected in the same manner as the first character. Then, the selection code is output at the timing of the final character through the switch. In this case, the data of the character before the last character can be read twice from the memory, but a simple latch circuit is used and the output of the comparator based on the data of the character before the last character is used as the code of the last character. There is no problem if you keep it until the output timing.

If the signal processing circuit of the present invention is applied to the OSD device of the closed caption system, the comparator for comparing the character data read from the memory with the blanking code and the transparent code and the output of the comparator are the same. If it is, a transparent code is selected. If it is not a match, a blanking code is selected and output.
The switch and the character data read out from the memory at the output timing of the first switch and the output code of the first switch at the character code output timing of the first character and the 34th character. Is optimally configured by a second switch for transmitting and outputting.

[0012]

1 is a block diagram showing a signal processing circuit of the present invention applied to an OSD device for displaying characters in a closed caption type teletext. First, the character data (VRAM Data) read from the VRAM in the OSD device (not shown) is input to the comparator 1 and compared with a specific character code. That is, the comparator 1
Is the read character data and blanking code (20
h: Hexa code), a first comparator 1a for comparing the read character data with the transparent code (00
and a second comparator 1b for comparing with h), and when the character data matches these codes, the comparison signal (EQU) is output via the OR gate.

The comparison signal from the comparator 1 is input to the latch circuit 2 and latched. The latch circuit 2 is configured to latch the comparison signal according to the comparison control signal,
This comparison control signal is a signal generated when the second character data is input for the first time and the 33rd character data is input as described later.

The comparison signal (EQUA) latched and output from the latch circuit 2 is input to the switch 3 to control selection of a predetermined character code. That is, the switching device 3 includes a first switching device 3a for selecting the blanking code and the transparent code.
a selects and outputs a blanking code if the comparison signal received at the selection terminal is logic 0, and outputs a transparent code if the comparison signal is logic 1. The output code of the first switch 3a is input to the second switch 3b,
It is selected and output at the character code output timing of the character or the character code output timing of the 34th character. The second switch 3b has a first character timing signal (Chr1) input to a selection terminal via an OR gate.
Or, the 34th character timing signal (Chr34) is logic 1
, The character code by the first switch 3a is selected and output. On the other hand, these timing signals are logic 0
In this case, the read character data (VRAM Data) from the VRAM is transmitted and output as a character code. That is, the first switch 3a and the second switch 3b function as a multiplexer.

FIG. 2 shows the output timing of the character code through the signal processing circuit. In this example, the character data of the second character stored at the beginning of each line is read twice from the VRAM. Therefore, the read character data is the second character → the second character → the third character. → The 4th character → …… is entered in that order. At this time, the comparison signal by the comparator 1 is the first second of the two times.
It is latched by the latch circuit 2 by the comparison control signal generated when the character data of the character is input, and simultaneously provided to the first switch 3a. In the illustrated example, since the character data of the second character is the code of the display character "A", the comparison signal indicates a logic 0, and therefore the blanking code is selected and output from the first switch 3a. When outputting the code of the first character, the first character timing signal is input to the second switch 3b at logic 1 simultaneously with the comparison control signal, so the second switch 3b outputs the output code of the first switch 3a. To output as a character code. When the second character data of the second character is input next time, since the first character timing signal becomes logical 0, the second switch 3b becomes the transmission selection of the read character data, and the character data of the second character is directly output as the character code. To be done. Thereafter, the read character data from the VRAM is transmitted and output.

Then, at the time of inputting the character data of the 33rd character stored at the end of each line, a comparison control signal is generated, and the comparison result of the character data of the 33rd character by the comparator 1 is latched in the latch circuit 2. . In the example shown,
Since the character data of the 33rd character is a blanking code, the comparison signal shows a logic 1, so that the first switch 3a selects the transparent code. Next, when the output of the character code of the 33rd character is completed and the output timing of the character code of the 34th character comes, the 34th character timing signal becomes logic 1, and the second switch 3b selects the output code of the first switch 3a. And output. In this case, similarly to the case of the first character, it is possible to read the character data of the 33rd character twice in succession and generate and output the character code of the 34th character. However, the latch circuit 2 latches the comparison signal. It is easier and easier to use.

When the character code for one line output according to the example of FIG. 2 is displayed, it becomes as shown in FIG. 3 (a). That is, the first character is a blanking character, the second character is a display character "A", the third to 32nd characters are similarly display characters, and the 33rd character is a blanking character and the 34th character is a transparent character. Will be done.
FIG. 3B shows another display example. In this character display, the signal processing circuit of this embodiment displays the transparent character of the first character based on the blanking character of the second character. , The 34th transparent character is displayed based on the 33rd transparent character.

[0018]

When the present invention is applied to the closed caption system, the memory can have a capacity of 32 characters × 15 lines even if 34 characters are displayed per line. Moreover, even if the capacity for one line is added, 32
Since a capacity of characters × 16 lines = 512 bytes is sufficient, smooth scroll display such as wraparound control can be realized by using the existing VRAM memory space.

[Brief description of drawings]

FIG. 1 is a block circuit diagram showing a configuration example of a signal processing circuit according to the present invention.

FIG. 2 is a timing diagram illustrating an output state of a character code by the signal processing circuit in FIG.

FIG. 3 is an explanatory diagram showing a display example of character display using the signal processing circuit of FIG. 1.

[Explanation of symbols]

 1 Comparator 1a 1st comparator 1b 2nd comparator 2 Latch circuit 3 Switching device 3a 1st switching device 3b 2nd switching device EQU, EQUA Comparison signal Chr1 1st character timing signal Chr34 34th character timing signal

Claims (5)

[Claims] 1. A character code control method for outputting a character code of a display character for displaying a teletext, comprising: reading out data of a second character at the timing of the first character of each line; A character code control method characterized by determining and outputting a character code of one character. 2. A character code control method for outputting a character code of a display character for displaying teletext, wherein the character code of the last character is determined from the character data before the last character of each line. Character code control method characterized by outputting at the timing of. 3. A character code control method for outputting a character code of a display character to display a teletext, comprising reading out data of a second character at the timing of the first character of each line, and reading the data of the second character from the data. A character code control method characterized by determining and outputting a character code of one character, determining the character code of the last character from the data of the character before the last character of each line, and outputting at the timing of the last character. 4. A signal processing circuit used in the character code control method according to claim 1, wherein the character data read from the memory is compared with a specific character code. A comparator and a predetermined character code are selected according to the output of the comparator and output at the timing of the first character and / or the last character, and from the memory at the timing of the character other than the first character and / or the last character. A switch for transmitting and outputting the read character data,
A signal processing circuit comprising: 5. A signal processing circuit used for an OSD device in closed caption type teletext, comprising:
A comparator for comparing the character data read from the memory with a blanking code and a transparent code, and a first switching device for selectively outputting a transparent code if the outputs of the comparator match and a blanking code if the outputs do not match. The output code of the first switching device is output at the character code output timing of the first character and the 34th character, and the character data read from the memory is transmitted at the character code output timing of the second character to the 33rd character. A second switching device for outputting, and a signal processing circuit.