JPH086758A - Memory access device for image display - Google Patents

Abstract

PURPOSE:To shorten a memory access time for display by eliminating a memory read of font data for the same character code. CONSTITUTION:This memory access device has a display address control part 33, a 1st character storage part 36, a 2nd character storage part 39, a code comparison part 41, a font address calculation part 43, a memory access part 46, and a font data storage part 51; when the code comparison part 41 decides that the same data are stored in the 1st and 2nd character storage parts, a character is displayed by using the data which are already stored in the font data storage part 51 without accessing the font data in the 1st character storage part for the character.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image display memory access device such as a personal computer or a word processor.

[0002]

2. Description of the Related Art In recent years, image display memory access devices have shortened the time for reading display data,
It has become possible to rewrite the display data from the etc. at high speed.

FIG. 3 is a block diagram of a conventional image display memory access device. In FIG. 3, 1 is a dot clock (DCL) indicating the time for one dot of the data to be displayed.
K), 2 is a character clock (CCLK) indicating the time for one character of the data to be displayed. A display address control unit 3 controls a memory address in which a character code to be displayed is stored.
Display address (DISADD) according to the rising edge of
4 and a character code request signal (CREQ) 5 having a length corresponding to one clock of the dot clock 1 are output. A character code storage unit 6 stores a character code to be displayed next, and outputs a character code (CDAT) 7 and a font address calculation request signal (FCAL) 8 at the rising edge of the dot clock 1. The font address calculation request signal 8 becomes “H” for one clock of the dot clock 1 when the font address calculation request is made. Reference numeral 9 denotes a font address calculation unit which receives a character code 7 and a font address calculation request signal 8 and calculates a memory address in which font data is stored from the character code. The font address calculation request signal 8 is set to "H". After that, the font address (FADD) 10 and the font data request signal (FR
EQ) 11 is output at the rising edge of dot clock 1. The font data request signal 11 outputs "H" for one clock of the dot clock 1 when there is a font data request. 12 is a memory access unit,
When the character code request signal 5 is active,
The address of the display address 4 is output to the memory address (MADD) 13 when the font data request signal 11 is active. When the memory access ends, the memory data valid signal (MRDY) 1 indicating that the memory access ends
In accordance with the rising edge of the dot clock 1, the "H" is output for 4 clocks of the dot clock 1. Reference numeral 15 denotes a memory, which stores data in the memory in the memory data bus (MDA
T) 16 is output. Reference numeral 17 is a font data storage unit for storing font data, and the font data (F
DAT) 18 is output. Reference numeral 19 denotes a data serializer, which outputs the font data 18 as dot data (FOUT) 20 one bit at a time in order from the upper bits in accordance with the rising edge of the dot clock 1. The character code storage unit 6 latches the memory data bus 16 at the rising edge of the dot clock 1 when the memory data valid signal 14 is "H" after the character code request signal 5 is "H". In the font data storage unit 17, after the font data request signal 11 becomes "H", the memory data bus 16 is started at the rise of the dot clock 1 when the memory data valid signal 14 is "H".
Latch.

The operation of the image display memory access device configured as described above will be described below with reference to FIG.
Will be described with reference to.

FIG. 4 is an operation explanatory diagram in the image display memory access device of FIG. In FIG. 4, the suffix H in the number means a hexadecimal number. The memory 15 has addresses 40H and 0001H at 0000H.
41H, 0400H contains 25H, and 0410H contains 30H. The character clock 2 is a clock obtained by dividing the dot clock 1 by 8.

First, at the rising edge of the character clock 2, 0000H is output from the display address control unit 3 to the display address 4 as a display address, and at the same time, the character code request signal 5 is set to "H" level for one clock of the dot clock 1. Become. In the memory access unit 12, since the character code request signal 5 becomes active, that is, becomes “H”, the address 0000H is output to the memory address 13 according to the address of the display address 4, and the memory according to the contents of the address of the memory address 13 40H is output from 15 to the memory data bus 16.

In the memory access unit 12, after the memory access, the memory data valid signal 14 indicating the end of the memory access becomes “H” for one clock of the dot clock 1 at the rising edge of the dot clock 1 and the dot clock 1 At the rising edge, it is latched in the character code storage unit 6, 40H is output to the CDAT 7, and the font address calculation request signal 8 becomes "H" for one clock of the dot clock 1.

In the font address calculation unit 9, since the font address calculation request signal 8 becomes "H", the CDA
The font address is calculated from the data 40H of T7, and 0
400H is output to the font address 10 according to the rising edge of the dot clock 1. At the same time, the font data request signal 11 becomes "H" for one clock of the dot clock 1, and the font data request is issued to the memory access unit 12. Since the font data request signal 11 has become “H”, the memory access unit 12 outputs the data 0400H of the font address 10 to the memory address 13 at the rising edge of the dot clock 1.

The memory 15 outputs the data 25H stored at the address 0400H to the memory data bus 16. In the memory access unit 12, the memory data valid signal 14 indicating that the memory access has ended becomes “H”, the data 25H of the memory data bus 16 is latched in the font data storage unit 17 at the rising timing of the dot clock 1, It is output to the font data 18.
The data serializer 19 outputs the font data 18 to the dot data 20 bit by bit from the upper bits in accordance with the rising edge of the dot clock 1.

Next, the character clock 2 rises, and the display address 4 becomes 0001H in the display address control unit 3. The same operation as above is performed,
The display continues.

[0011]

However, in the above-mentioned conventional configuration, even when the consecutive character codes are the same, the font data is accessed for each character to the memory, so It has a drawback that it takes time to access the memory.

The present invention solves the above-mentioned conventional problems. When the consecutive character codes are the same, the memory access for the font data is limited to the first character so that the display data for the display data can be obtained. Memory access time is greatly reduced.

[0013]

To achieve this object, an image display memory access device of the present invention comprises a display address control unit for controlling a memory address in which a character code for display is stored, The first character code storage unit stores the currently displayed character code, the second character code storage unit stores the next character code to be displayed, and the first character code storage unit. A character code comparison unit that compares data with data in the second character storage unit, and a memory address where font data corresponding to the character code stored in the second character code storage unit are stored. A font address calculator, an address of the display address controller, and the font address calculator Selects the address, and a memory access unit for performing memory access.

[0014]

According to the above construction, the character code comparing means for comparing the character code currently displayed with the character code to be displayed next is provided, and when the comparison results match, that is, the characters having the same character code are consecutive. In the case of displaying the data, the memory access next to the font data is not performed, so that the memory access time for the display data can be significantly reduced.

[0015]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of an image display memory access device according to an embodiment of the present invention. In FIG. 1, 31 is a dot clock indicating the time for one dot of the displayed data, and 32 is a character clock indicating the time for one character of the displayed data. A display address control unit 33 controls the memory address in which the character code to be displayed is stored.
At the rising edge of 2, the display address 34 and the character code request signal 35 are output. The character code request signal 35 indicates that when a character code is requested,
It becomes "H" only for one clock of the dot clock 31. A first character code storage unit 36 stores a character code to be displayed next, and outputs the first character code 37 and the font address calculation request signal 38 at the rising edge of the dot clock 31. The font address calculation request signal 38 becomes "H" for one clock of the dot clock 31 when there is a font address calculation request. Reference numeral 39 denotes a second character code storage unit that stores the currently displayed character code, which latches the first character code 37 and outputs the second character code 40 at the rising edge of the character clock 32. 41 is the first character code 3
It is a code comparison unit that receives 7 and the second character code 40 as input and detects that two data are equal, and outputs a match detection signal 42. The match detection signal 42 is "H" when they match, and "L" when they do not match.
Is output. Reference numeral 43 denotes a font address calculation unit that receives the first character code 37, the font address calculation request signal 38, and the match detection signal 42 as input, and calculates the memory address where the font data is stored from the character code. The font data request signal 45 is output at the rising edge of the dot clock 31. The font data request signal 45 is the match detection signal 4
Font address calculation request signal 3 when 2 is "L"
When 8 becomes "H", it becomes "H" only for one clock of the dot clock 31. A memory access unit 46 stores the address of the display address 34 when the character code request signal 35 becomes "H" and the address of the font address 44 when the font data request signal 45 becomes "H". Output to address 47. When the memory access is completed, the memory access unit 46 outputs “H” for one clock of the dot clock 31 in response to the rising edge of the dot clock 31 in the memory data valid signal 48 indicating that the memory access is completed. Reference numeral 49 is a memory, which outputs data in the memory to the memory data bus 50 in accordance with the address of the memory address 47. A font data storage unit 51 stores font data, and outputs font data 52. Reference numeral 53 is a data serializer, which sets the font data 52 according to the rising edge of the dot clock 31.
Dot data 54 bit by bit in order from the upper bit
Output as First character code storage unit 36
Latches the memory data bus 50 at the rising edge of the dot clock 31 when the memory data valid signal 48 becomes "H" after the character code request signal 35 becomes "H". In the font data storage unit 51, the memory data bus 50 is latched at the rise of the dot clock 31 when the memory data valid signal 48 becomes "H" after the font data request signal 45 becomes "H". .

The operation of the image display memory access device configured as described above will be described with reference to FIG.

FIG. 2 is an operation explanatory diagram of the image display memory access device of FIG. In FIG. 2, H at the end of the numbers means hexadecimal numbers. The memory 49 has addresses 0000H, 30H, 0001H
40H, 0002H 40H, 0400H 25H,
It is assumed that 30H is contained in 0300H. The character clock 32 is a clock obtained by dividing the dot clock 31 by eight.

First, at the rising edge of the character clock 32, the display address 34 is displayed by the display address controller.
0001H is output, and at the same time, the character code request signal 35 goes high for one clock of the dot clock 31. In addition, the second character code storage unit 39 latches the content 30H of the first character code 37 at the rising edge of the character clock 32 and outputs 30H to the second character code 40.
In the memory access section 46, since the character code request signal 35 is active, that is, becomes "H", the address 0001H of the display address 34 is changed to the memory address 47.
Output to. The memory 49 outputs the content 40H of the address 0001H to the memory data bus 50.

In addition, in the memory access unit 46, in order to indicate that the memory access is completed, the memory data valid signal 48 indicating the end of the memory access is set to "H" for one clock of the dot clock 31 in accordance with the rise of the dot clock 31. " In the first character code storage unit 36, the character code request signal 35 is "H".
After that, since the memory data valid signal 48 becomes "H", the content 40H of the memory data bus 50 is latched and 40H is output to the first character code 37.
At the same time, the font address calculation request signal 38 is set to "H".

In the code comparison section 41, since the contents of the first character code 37 and the first character code B40 are different between 40H and 30H, the match detection signal 42
To "L". Since the font address calculation request signal 38 becomes "H" in the font address calculation unit, the font address is calculated from the content of the first character code 37, and 0400H is output to the font address 44 according to the rise of the dot clock 1. . Since the match detection signal 42 is "L", the font data request signal 45 is "H" for one clock of the dot clock 31.
And request memory access. Memory access unit 4
6, the font data request signal 45 becomes "H", and therefore the data 0400H of the font address 44 is output to the memory address 47 in accordance with the rising of the dot clock 31.

The memory 49 outputs the data 25H stored at the address 0400H to the memory data bus 50. In the font data storage unit 51, since the memory data valid signal 48 becomes "H" after the font data request signal 45 becomes "H", the memory data bus 5
The data 25H of 0 is latched and output to the font data 52 at the rising edge of the dot clock 31. The data serializer 53 outputs the font data 52 bit by bit from the upper bits to the dot data 54 in accordance with the rise of the dot clock 31.

At the next rise of the character clock 32, the display address 34 changes to the next address 0002H, and the character code request signal 35 becomes "H" again. Further, in the second character code storage section, the first character code 37 is latched at the rising edge of the character clock 32, and the second character code 40 becomes 4
Output 0H. In the memory access section 46, since the character code request signal 35 is "H", the display address 3
The address 0002H of No. 4 is output to the memory address 47 at the rising edge of the dot clock 31. The memory 49 outputs the content 40H of the address 0002H to the memory data bus 50.

The memory access section 46 sets the memory data valid signal 48 to "H" for one clock of the dot clock 31 in order to indicate that the memory access is completed. In the first character code storage unit 36, since the memory data valid signal 48 becomes "H" after the character code request signal 35 becomes "H", the content 40H of the memory data bus 50 is latched, 40H is output to the first character code 37. At the same time, the font address calculation request signal 38 is set to "H".

In the code comparison section 41, since the contents of the first character code 37 and the first character code B40 are the same at 40H and 40H, respectively, the match detection signal 42
To "H". Since the font address calculation request signal 38 has become “H”, the font address calculation unit calculates the font address according to the first character code 37 and outputs 0400H to the font address 44. However, since the coincidence detection signal 42 is “H”,
The font data request signal 45 remains "L". Therefore, no memory address is generated and the content of the font data storage unit 51 does not change. Since the font data 52 continues to output 25H, the data serializer 53 outputs the same data for two characters as the dot data 54.

[0026]

The memory access device for image display of the present invention compares the character code currently displayed with the character code to be displayed next, and as a result, when both character codes match, font data is displayed. Since the same character is continuously displayed without performing the next memory access, the memory access time for display data can be significantly reduced.

[Brief description of drawings]

FIG. 1 is a block diagram of a memory access device for image display according to the present invention.

FIG. 2 is an operation explanatory diagram of the image display memory access device of the present invention.

FIG. 3 is a block diagram of a conventional image display memory access device.

FIG. 4 is an operation explanatory diagram of a conventional image display memory access device.

[Description of Codes] 1 dot clock (DCLK) 2 character clock (CCLK) 3 display address control unit 4 display address (DISADD) 5 character code request signal (CREQ) 6 character code storage unit 7 character code (CDAT) 8 font address Calculation request signal (FCAL) 9 Font address calculation unit 10 Font address (FADD) 11 Font data request signal (FREQ) 12 Memory access unit 13 Memory address (MADD) 14 Memory data valid signal (MRDY) 15 Memory 16 Memory data bus ( MDAT) 17 font data storage unit 18 font data (FDAT) 19 data serializer 20 dot data (FOUT) 31 dot clock (DCLK) 32 character clock CCLK) 33 Display address control unit 34 Display address (DISADD) 35 Character code request signal (CREQ) 36 First character code storage unit 37 First character code (CDATA) 38 Font address calculation request signal (FCAL) 39 Second Character code storage unit 40 Second character code (CDATB) 41 Code comparison unit 42 Match detection signal (EQ) 43 Font address calculation unit 44 Font address (FADD) 45 Font data request signal (FREQ) 46 Memory access unit 47 Memory Address (MADD) 48 Memory data valid signal (MRDY) 49 Memory 50 Memory data bus (MDAT) 51 Font data storage unit 52 Font data (FDAT) 53 Data serializer 54 Ttodeta (FOUT)

Claims (2)

[Claims] 1. A character code comparing means for comparing a currently displayed character code with a character code to be displayed next, and when the comparison result matches, the next memory access of the font data is not performed. An image display memory access device. 2. A display address control unit for controlling a memory address in which a character code for display is stored, a first character code storage unit for storing the currently displayed character code, and A second character code storage unit for storing a character code to be displayed; a character code comparison unit for comparing data in the first character code storage unit with data in the second character code storage unit; The font address calculation unit for calculating the memory address where the font data corresponding to the character code stored in the second character code storage unit is stored, the address of the display address control unit and the address of the font address calculation unit. For image display with memory access unit for selecting and accessing memory Memory access device.