JP2004085967A - Character display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a character display device of which the memory power consumption is reduced when continuously displaying the same characters. <P>SOLUTION: The character display device includes a display information memory wherein the character address of a display character in each display position on a display picture is stored, a character memory wherein character data of each character address is stored, a memory control circuit which sequentially reads out character addresses from the display information memory synchronously with a synchronizing signal of the display picture, and a control unit which accesses the character memory to read out character data from a present character address when the present character address differs from the just preceding character address out of character addresses sequentially read out from the display information memory and does not access the character memory when the present character address is coincident with the just preceding character address. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention generally relates to a display device for displaying information on a display screen, and more particularly, to a character display device for displaying character information on a display screen.
[Prior art]
Recent display devices have made it possible to display more information with a large screen size and provide higher image quality with a high-resolution display. In the character display device, in order to realize such a large-screen display and a high-resolution display, it is necessary to increase the display memory area and increase the operating frequency. As a result, the power consumption increases, and a voltage drop occurs in the central portion of the LSI chip, causing a malfunction or generating heat due to power consumption. Therefore, it is necessary to reduce useless power in the character display device as much as possible.
[0002]
FIG. 1 is a diagram showing an example of the configuration of a conventional character display device.
[0003]
The character display device 10 of FIG. 1 includes a display information memory 11, a character memory 12, a memory control circuit 13, and a display control unit 14.
[0004]
The display information memory 11 is a memory that stores, for each display position address indicating a two-dimensional position on the display screen, information indicating display contents, that is, a code for specifying a character to be displayed, a character display attribute, and the like. The character memory 12 is a memory for storing data used for displaying each character to be displayed, that is, bitmap data expressing the shape of each character. The memory control circuit 13 is a circuit that controls the display information memory 11, the character memory 12, and the display control unit 14.
[0005]
FIG. 2 is a timing chart showing the operation of the character display device 10 of FIG.
[0006]
The memory control circuit 13 supplies a display position address (FIG. 2A) and an access timing signal (FIG. 2B) to the display information memory 11. As a result, a code for specifying a character to be displayed at the specified display position address is read from the display information memory 11 at the specified access timing. The code specifying the read character is supplied to the character memory 12 as a character address (FIG. 2C). By specifying the address in the character memory 12 by the character address, the character data of the display character (FIG. 2 (g)) is read from the character memory 12. The timing at which the character data of the display character is read from the character memory 12 is determined by the character access timing (FIG. 2E) supplied from the memory control circuit 13 to the character memory 12.
[0007]
From the display information memory 11, at the same time as reading a character address which is a code for specifying a character, a character attribute (FIG. 2D) for specifying an attribute such as a color or decoration of the character is read. The character attribute and the character data are read into the display control unit 14 by a character read timing signal (FIG. 2 (h)). This character read timing signal is a signal supplied from the memory control circuit 13 to the display control unit 14.
[0008]
The display control unit 14 processes the read character data according to the read character attributes and supplies the processed character data to a display device such as a CRT, a liquid crystal display device, or a plasma display device.
[Problems to be solved by the invention]
In the conventional character display device as described above, even when the same character is displayed continuously, character data is read from the character memory 12 and supplied to the display control unit 14 one by one. For example, even when characters are displayed only on a part of the screen and other characters are blank characters, in the conventional control, the operation of reading the blank character data from the character memory 12 is repeated the number of times the blank characters are repeated. . For example, when a ruled line of a table is displayed on a screen, it is necessary to read out ruled line character data by the number of characters corresponding to the length of the ruled line.
[0009]
As described above, in the related art, when reading the same character, the display is performed without special control on the continuation of the same character, so that the memory access of the same continuous data is frequently repeated. It wastes power.
[0010]
In view of the above, an object of the present invention is to provide a character display device in which power consumption is reduced by reducing the number of memory accesses when displaying the same continuous character.
[Means for Solving the Problems]
A character display device according to the present invention includes: a display information memory for storing a character address for a display character for each display position on a display screen; a character memory for storing character data for each character address; A memory control circuit for sequentially reading the character address from the display information memory; and accessing the character memory when the current character address in the character address sequentially read from the display information memory is not the same as the immediately preceding character address. A control unit that reads out the character data from the current character address and does not execute access to the character memory when the current character address is the same as the immediately preceding character address. .
[0011]
According to the character display device, when displaying the same character continuously, the same character data already output is repeatedly displayed without newly accessing the character memory. This makes it possible to reduce the number of times of memory access when displaying the same continuous character, thereby reducing power consumption.
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
[0012]
FIG. 3 is a diagram showing an example of the configuration of the character display device according to the present invention.
[0013]
3 includes a display information memory 21, a character memory 22, a memory control circuit 23, a display control unit 24, a continuous state control & special character control unit 25, a latch 26, and a special character control unit 27.
[0014]
The display information memory 21 is a memory that stores, for each display position address indicating a two-dimensional position on the display screen, information indicating display contents, that is, a code for specifying a character to be displayed, a character display attribute, and the like. The character memory 22 is a memory for storing data used for displaying each character to be displayed, that is, bitmap data expressing the shape of each character. The memory control circuit 23 is a circuit that controls the display information memory 21, the character memory 22, and the display control unit 24.
[0015]
The continuous state control & special character control unit 25 is provided between the memory control circuit 23 and the character memory 22, and functions to restrict access to the character memory 22 by the memory control circuit 23 depending on the situation.
[0016]
More specifically, the continuous state control & special character control unit 25 receives the character address from the display information memory 21 and, at the timing designated by the character address comparison timing received from the memory control circuit 23, sets the current character address and the immediately preceding character. Compare with address. If the two character addresses do not match, the character access timing signal received from the memory control circuit 23 is supplied to the character memory 22 as it is. When both character addresses match, that is, when the same character is displayed continuously, no character access timing signal is supplied to the character memory 22. This makes it possible to avoid accessing the character memory 22 when displaying the same character continuously. In this case, the character data of the immediately preceding display character is stored in the latch 26, and the display is performed using the character data of the latch 26.
[0017]
The continuous state control & special character control unit 25 further controls to stop access to the character memory 22 in the case of a special character. This is determined based on the character attributes supplied from the display information memory 21. When the character attribute indicates a predetermined special character (for example, a blank character), the continuous state control & special character control unit 25 does not supply the character access timing signal supplied from the memory control circuit 23 to the character memory 22. As will be described later, the special character processing in this case is performed by the special character control unit 27.
[0018]
FIG. 4 is a timing chart showing the operation of the character display device 20 of FIG.
[0019]
The memory control circuit 23 supplies a display position address (FIG. 4A) and an access timing signal (FIG. 4B) to the display information memory 21. As a result, the character address (FIG. 4C) for specifying the character to be displayed at the specified display position address is read from the display information memory 21 at the specified access timing. Further, from the display information memory 21, character attributes (FIG. 4D) for specifying attributes such as character color and decoration are read. By specifying an address in the character memory 22 by the character address, the character data of the display character is read from the character memory 22.
[0020]
The timing of reading the character data of the display character from the character memory 22 is determined by the character access timing (FIG. 4E) supplied from the memory control circuit 23 to the character memory 22 via the continuous state control & special character control unit 25. Is done. In the example shown in FIG. 4C, the character address of the first character is “1A”, and in response, a character access timing signal (FIG. 4E) is supplied to the character memory 22 and the character data “ CC "(FIG. 4 (g)). The character address of the second character is "02". In response to this, a character access timing signal is supplied to the character memory 22, and the character data "11" is read.
[0021]
Since the character address of the third character is “02”, which is the same as the character address of the second character, in this case, the character access timing signal is not supplied to the character memory 22 (FIG. 4E). Since the immediately preceding character data "11" is stored in the latch 26 shown in FIG. 3, the character data supplied to the display control unit 24 remains "11" (FIG. 4 (g)).
[0022]
Thereafter, the character addresses of the fourth and fifth characters are also the same "02", and the character access timing signal is not supplied to the character memory 22. During this time, the character data "11" stored in the latch 26 is repeatedly supplied to the display control unit 24 (FIG. 4 (g)).
[0023]
The character address of the sixth character is “21” (FIG. 4C), and the character attribute is “C3” (FIG. 4D). In this example, the character attribute corresponds to a blank character that the continuous state control & special character control unit 25 regards as a special character. In this case, the character access timing signal is not supplied to the character memory 22 (FIG. 4E). The special character control unit 27 supplied with the character attribute of the blank character replaces the character data supplied from the latch 26 with zero data. As a result, the character data supplied to the display control unit 24 becomes “00” indicating a blank (FIG. 4G).
[0024]
The display control unit 24 reads character data and character attributes according to a character read timing signal from the memory control circuit 23, processes the character data according to the character attributes, and displays a CRT, a liquid crystal display device, and a plasma display device. And the like.
[0025]
As described above, in the character display device 20 according to the present invention, when displaying the same character continuously, the character data stored in the latch 26 is repeatedly displayed without accessing the character memory 22. . This makes it possible to reduce the number of times of memory access when displaying the same continuous character, thereby reducing power consumption. Further, in the character display device 20 according to the present invention, in the case of a predetermined special character such as a blank character, the special character control unit 27 generates the special character without accessing the character memory 22. This makes it possible to reduce the number of memory accesses when displaying special characters such as blanks and ruled line characters, thereby reducing power consumption.
[0026]
In the character display device 20 of the present invention shown in FIG. 3, various modifications can be made. For example, from the viewpoint of continuous display of the same character, the latch 26 is not always necessary. If the output of the character memory 22 does not change when there is no new access, the output of the character memory 22 is directly sent to the special character control unit 27. It may be configured to input. If it is not necessary to control the character memory 22 in the case of special characters, the special character control unit 27 may be deleted. The latch 26 can be used to enable character display without accessing the character memory 22 when data is written to the character memory 22 as described later.
[0027]
FIG. 5 is a diagram showing an example of a screen display of the character display device 20 according to the present invention.
[0028]
The character display device 20 can be used, for example, when performing various settings such as screen adjustment in a television set or a display device. FIG. 5 shows a setting menu screen. For example, it is possible to shift to a screen for adjusting color, brightness, and the like by specifying an item of screen adjustment. In the screen as shown in FIG. 5, a character display area 32 of, for example, 45 digits × 16 lines is set in the CRT display area 31, and the character display device 20 displays characters in the character display area 32. For example, the character display device 20 displays the display ruled line frame 33 and displays the display characters 34 in the frame.
[0029]
In the example shown in FIG. 5, the outside of the display ruled line frame 33 is an area where the same blank characters are continuously displayed. Therefore, in the character display device 20 according to the present invention, the power consumption can be reduced without accessing the character memory in such a display region of the same character continuously. Also, the horizontal line of the display ruled line frame 33 is a portion where the same ruled line character is continuous, and power consumption can be reduced. Further, as described above, even when the same character is not continuous, when displaying a predetermined special character such as a blank character, power consumption can be reduced without accessing the character memory.
[0030]
FIG. 6 is a circuit diagram showing an example of the configuration of the continuous state control & special character control unit 25. FIG. 7 is a timing chart showing the timing of each signal of the continuous state control & special character control unit 25 shown in FIG.
[0031]
The continuous state control & special character control unit 25 of FIG. 6 includes flip-flops 41 and 42, a comparator 43, and an AND circuit 44 having a partially negative logic input. The flip-flop 41 latches the character address (FIG. 7A) in synchronization with the character access timing signal (FIG. 7B). The comparator 43 compares the currently supplied character address with the character address stored in the flip-flop 41, and outputs a HIGH signal when both characters match. The flip-flop 42 latches the output of the comparator 43 in synchronization with the character address comparison timing signal (FIG. 7C). The data stored in the flip-flop 42 is a comparison result (FIG. 7D) indicating whether the current display character is the same as the immediately preceding display character.
[0032]
The AND circuit 44 receives, as a first input, a negative logic of a bit (FIG. 7 (e)) indicating whether or not it is a blank character among a plurality of bits of the character attribute, and outputs an output of the flip-flop 42 (FIG. 7 (d)) is received as a second input, and the character access timing (FIG. 7 (b)) from the memory control circuit 23 is received as a third input. Therefore, the character access timing passes through the AND circuit 44 only when the display character is other than a blank character, the first input is HIGH, and the second input is HIGH because the display character is different from the immediately preceding character. Then, it is output from the continuous state control & special character control unit 25 (FIG. 7 (f)). When the display character is a blank character or when the display character is the same as the immediately preceding character, the output of the AND circuit 44 becomes LOW, and the character memory 22 is not accessed.
[0033]
FIG. 8 is a diagram showing an example of the configuration of the special character control unit 27.
[0034]
As shown in FIG. 8, the special character control unit 27 includes an AND circuit 51 of which one has a negative logic input. FIG. 8 shows only the configuration for one bit of the character data. For example, when the character data has eight bits for one scanning line, the AND circuit 51 of FIG. 8 is provided for eight bits.
[0035]
To the negative logic input terminal of the AND circuit 51, a bit indicating whether or not it is a blank character among a plurality of bits of the character attribute is input. The other end of the AND circuit 51 is supplied with one bit of character data. When the display target character is a blank character, the logic of the negative logic input side of the AND circuit 51 becomes negated, and the output of the AND circuit 51 becomes LOW. Similarly, the output data becomes LOW (zero) for all bits of the character data, and blank character data is generated and output.
[0036]
FIG. 9 is a timing chart for explaining the operation of the latch 26 when writing to the character memory 22 is performed.
[0037]
The character memory 22 may use a ROM (Read Only Memory), but may use a RAM (Random Access Memory) to enable writing by a user. With such a configuration, the contents of the character memory 22 may be rewritten during the character display by the character display device 20.
[0038]
The character address shown in FIG. 9A is an input address to the character memory 22. The first character address is "1A", and the second to fifth character addresses are "02", and the operation is to continuously display the same character. Therefore, in this case, even if the character access timing signal (FIG. 9B) is input to the continuous state control & special character control unit 25, the new character access timing (FIG. 9C) is not output in the continuous display section.
[0039]
In such a continuous display state, writing to the character address “41” of the character memory 22 is performed from the outside at the timing indicated as “writing timing occurrence”. At this time, at the timing indicated by the character write timing signal (FIG. 9D) supplied to the character memory 22, the input / output character data (FIG. 9E) of the character memory 22 is written to write the character data. It becomes address data.
[0040]
If the latch 26 is provided as shown in FIG. 3 to latch the character data output from the character memory 22 at the character access timing from the continuous state control & special character control unit 25, the structure shown in FIG. Even if the data in the character memory 22 changes, the data in the latch 26 continues to be held during the continuous display as shown in FIG. Therefore, during the continuous display period, normal character display can be performed even if data writing occurs. Even after the end of the continuous display, as shown in FIG. 9, if the character to be subsequently displayed is a predetermined special character (a blank character in this example), the character is designated by the processing of the special character control unit 27. Special characters can be displayed.
[0041]
As described above, the present invention has been described based on the embodiments. However, the present invention is not limited to the above embodiments, and various modifications can be made within the scope of the claims.
【The invention's effect】
In the character display device according to the present invention, when the current character address is not the same as the immediately preceding character address in the character addresses sequentially read from the display information memory, the character memory is accessed to read the character data from the current character address. . However, if the current character address is the same as the immediately preceding character address, no access is made to the character memory.
[0042]
According to the character display device, when displaying the same character continuously, the same character data already output is repeatedly displayed without newly accessing the character memory. This makes it possible to reduce the number of times of memory access when displaying the same continuous character, thereby reducing power consumption.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating an example of a configuration of a conventional character display device.
FIG. 2 is a timing chart showing an operation of the character display device of FIG. 1;
FIG. 3 is a diagram showing an example of a configuration of a character display device according to the present invention.
FIG. 4 is a timing chart showing an operation of the character display device of FIG. 3;
FIG. 5 is a diagram showing an example of a screen display of the character display device according to the present invention.
FIG. 6 is a circuit diagram showing an example of a configuration of a continuous state control & special character control unit.
FIG. 7 is a timing chart showing the timing of each signal of the continuous state control & special character control unit.
FIG. 8 is a diagram illustrating an example of a configuration of a special character control unit.
FIG. 9 is a timing chart for explaining the function of a latch when data is written to a character memory;
[Explanation of symbols]
Reference Signs List 20 character display device 21 display information memory 22 character memory 23 memory control circuit 24 display control unit 25 continuous state control & special character control unit 26 latch 27 special character control unit

Claims (8)

A display information memory for storing a character address for a display character for each display position on the display screen;
A character memory for storing character data for each character address,
A memory control circuit for sequentially reading the character address from the display information memory in synchronization with a display screen synchronization signal;
If the current character address of the character addresses sequentially read from the display information memory is not the same as the immediately preceding character address, the character memory is accessed to read the character data from the current character address, and A character display device comprising a control unit that does not execute access to the character memory when the address is the same as the immediately preceding character address. The control unit comprises:
A flip-flop for storing the immediately preceding character address;
A comparator for comparing the current character address with the content of the flip-flop;
2. The character display device according to claim 1, further comprising a circuit for switching between supply and suspension of an access timing signal for accessing said character memory to said character memory in accordance with a comparison result of said comparator. 2. The character display device according to claim 1, further comprising a latch circuit that latches and holds the character data output from the character memory only when the control unit accesses the character memory. 4. The character display device according to claim 3, wherein said character memory is a writable memory during a display operation. The display information memory stores a character attribute of the display character together with the character address, and the memory control circuit sequentially reads the character address from the display information memory and simultaneously reads the character attribute. 4. The character display device according to claim 1, wherein access to the character memory is not performed when the output character attribute indicates a predetermined character. The control unit comprises:
A flip-flop for storing the immediately preceding character address;
A comparator for comparing the current character address with the content of the flip-flop;
6. A circuit according to claim 5, further comprising a circuit for switching supply and stop of an access timing signal for accessing said character memory to said character memory in accordance with a comparison result of said comparator and said read character attribute. Character display device. 6. A special character control unit for changing character data to be displayed on the display screen to character data of the predetermined character when the read character attribute indicates the predetermined character. The character display device as described in the above. The predetermined character is a blank character, and the special character control unit sets a mask circuit for setting all bits of character data to be displayed on the display screen to zero when the read character attribute indicates the predetermined character. The character display device according to claim 7, further comprising:

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