JP2846357B2 - Font memory device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a font memory device capable of effectively utilizing a character generator having a limited memory capacity.

2. Description of the Related Art In general, a display device can display fonts of various sizes. These fonts are stored in different character generator ROMs for each size.

[Problems to be Solved by the Invention] However, in the conventional device, a character generator ROM is required for the number of required font sizes, and the area occupied by the substrate on which the character generator ROM is provided is increased. In addition to hindrance, there was a problem of cost increase.

Therefore, the present invention has been made in view of the above-described problems, and an object of the present invention is to provide a character generator ROM.
Character generator RO by effectively utilizing
An object of the present invention is to provide a font memory device which can obtain fonts of various sizes even if the number of M is small and can reduce the cost.

[Means for Solving the Problems] To achieve the above object, a font memory device according to the present invention comprises a character generator (5) capable of storing a plurality of fonts having different numbers of dots in a memory area indicated by the same character code. A selector for selecting a font having a different number of dots stored in the character generator based on the selection of the character generator read bit, and outputting an enable signal to a register corresponding to the font; And a register (7) for latching the font of the desired dot output from the character generator in response to the switching of the bits in the line count address and receiving and outputting an enable signal.

[Operation] According to the above configuration, since a plurality of fonts having different numbers of dots are stored in the memory area indicated by the same character code, the selection of the character generator read bit and the switching of the line count address bit change the plurality of fonts. A font with a desired number of dots can be obtained.

FIG. 1 is a block diagram showing an embodiment of a font memory device according to the present invention.

The font memory device according to this embodiment has the same character generator
M, data can be read from CPU 1, data writing means 2, CRT controller 3, code buffer 4,
It has a schematic configuration including a character generator 5, a selector 6, and a register 7.

CPU 1 writes data to code buffer 4, which is a part of the address of character generator 5, into data writing means 2.
Output to

This data is composed of a character generator read bit A and a character code B as shown in FIG. Character generator read bit A
Is the information for switching the font size (24 dots and 16 dots) of the font data to be read, the designation of full-width or half-width, and in the case of full-width, the information to specify the left and right half of the full-width, the distinction between kanji and ANK etc. The character code B is a code indicating prescribed information, and the character code B is an address of a character stored in the character generator 5.

The data writing means 2 is composed of two registers 2a and 2b for latching the data of the character generator read bit A and the character code B described above.
Then, these data are simultaneously written to the code buffer 4 by an enable signal issued at a predetermined timing from the CRT controller 3.

The CRT controller 3 outputs a code buffer address to the code buffer 4, outputs a line count address C to the character generator 5, and updates the line count address for each line.

Line count address C is the address for scanning a dot line on the display screen, one bit C ₁ of the top of the address as shown in FIG. 2 (b) is 24 dots as the font size has been selected When 16 dots are selected, the selector 6 outputs a left / right switching signal to the multiplexer based on the character generator read bit A output from the CPU 1 and outputs the left / right switching bit to the line count address C. the addition of C _1.

The line count address C is sequentially updated by a raster scan type CRT controller 3.

The code buffer 4 outputs data corresponding to the code buffer address output from the CRT controller 3 onto the first display bus 8.

The character generator 5 includes a first character generator 5a and a second character generator 5b.

Each of the character generators 5a and 5b receives the data from the code buffer 4 output on the first display bus 8 (ie, the character generator read bit A and the character code B), the line count address C from the CRT controller, and the data from the selector 6. Both output the font data to the register 7 at the subsequent stage based on the switching signal.

The character generators 5a and 5b will be further described. As shown in FIG. 3, the first character generator 5a stores 16-bit data D1 of the 24-dot font data and the second character generator 5a. 5b stores the remaining 8-bit data D2 of the 24-dot font data and the 16-dot font data d1 and d2, which are vertically divided in half-width units.

Both the 24-dot font and the 16-dot font are the same character and are provided in the address area indicated by the same character code B.

Register 7 has four registers 7 for latching font data output from each of character generators 5a and 5b.
a, 7b, 7c, 7d. First register 7a is among the data D1 of the first character generator 5a, which latches the 12-bit data D1 ₁ corresponding to the left half of the font data of 24 dots.

The second register 7b includes a first character generator
The remaining 4-bit data D1 ₂ of the data of 5a, and the second
And latches the 8-bit data D2 character generator 5b of 2 together with the data D1 ₂ and data d2
It corresponds to the right half of 4-dot font data.

When the most significant bit C ₁ of the line count address C indicates 0, the third register 7c are latches 8 bit data d1 of the second character generator 5b corresponding to the left half of the font data 16 dots .

When the most significant bit C ₁ of the line count address C indicates a 1, the fourth register 7d, the second character generator 5b corresponding to the right half of the 16-dot font data
Is latched for the remaining 8-bit data d2.

The font data latched in the register 7 is output onto the second display bus 9 by supplying an enable signal from the selector 6, and is subjected to D / A conversion in a circuit (not shown) at a subsequent stage, and then the video signal Is displayed on the display screen of the display.

The selector 6 controls access to font data in the character generator 5 based on the character generator read bit A output from the code buffer 4.

The multiplexer receives the left / right switching signal output from the selector 6 based on the character generator read bit A output from the CPU 1 and receives the line count address C
Adding switching bit C ₁ of the left and right.

Next, an operation of accessing font data according to the above configuration will be described.

First, when the content of the character generator read bit A from the code buffer 4 indicates 24-dot full-width font data and the character code B designates the "Han" character shown in FIG. The first line of the font data D1, D2, d1 is output from the first and second character generators 5a, 5b so that the 24-dot "kan" font data is output to the display bus 9, register font data D1 ₁ of the font data D1 in the register 7a is, font data D1 ₂ and font data D2 in the second register 7b is a third 7
The font data d1 is latched in c.

Next, the selector 6 sequentially outputs an enable signal to the first and second registers 7a and 7b among the registers 7a, 7b and 7c, and outputs a "24-dot full-width" Kan "on the second display bus 9. The first line of the font data is output 12 bits at a time.

Then, when the line count address C is updated by the CRT controller 3, the font data of the second line of "Kan" is output onto the second display bus 9, and this is repeated 24 times in total.

On the other hand, a case will be described in which the content of the character generator read bit A indicates 16-dot full-width font data and the character code B indicates "Han" font data.

First, when the switching bit C ₁ of the line count address C to be input from the selector 6 is multiplexer is "0", in the first, second character generator 5a, font data D1, D2 and 16-dot font data from 5b The first line of the data d1 corresponding to the left half is output and latched by the first, second, and third registers 7a, 7b, 7c.

The first, second character generator 5a, 17 line and 16-dot font data D1, D2 from 5b when the switch bits C ₁ of the line count address C to be input from the selector 6 are multiplexed is "1" The first line of data d2 corresponding to the right half of the font data is output and latched by the first, second and fourth registers 7a, 7b and 7c. Then, when the enable signal is sequentially output from the selector 6 to the third and fourth registers 7c and 7d among the registers 7a, 7b, 7c and 7d, the latched font data is output on the second display bus 9. Is output to

Next, when the line count address C is updated by the CRT controller 3, the font data of the second line of "KAN" is output onto the second display bus 9, and this is repeated a total of 16 times, and "KAN" is repeated. Will be output as a whole.

When the character generator read bit A designates the left half width of a full-width character with 24 dots, the character generator read bit A described above is used until the font data of the register 7 is latched.
24 is the same as is the case indicate a full-width font data dot, an enable signal from the next selector 6 registers 7a only because it is output to the 12 dot font data D1 ₁ 1 th line of the second Output to the display bus 9. This is repeated 24 times in total, and the entire font data corresponding to the desired left half-width character is output.

Similarly, the character generator read bit A is set to 24
If the dot specifies the right half-width of full-width characters,
Since the enable signal from the selector 6 is output only to the second register 7b, a total of 12 dot font data
D1 1 line ₂ and D2 is a second display bus 9
Output above. This is repeated 24 times in total, and the entire font data corresponding to the desired right half-width character is output.

In the above operation, the character generator
When font data is stored in 5a and 5b, reading of the font data has been described.To write font data to the character generators 5a and 5b, the CPU 1 starts a font creation program, and A font is created for each line count address assigned to each font.

[Effects of the Invention] As described above, according to the font memory device of the present invention, a plurality of font data having different numbers of dots are stored in the memory area indicated by the same character code, and can be effectively read out. Therefore, a large number of font data can be obtained with a small number of character generators. As a result, the area occupied by the substrate required for the character generator can be reduced, and the entire apparatus can be reduced in size and cost.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of a font memory device according to the present invention. FIGS. 2 (a) to 2 (c) are diagrams showing a data structure for designating an address to a character generator in the device. FIG. 2A shows the structure of data from the code buffer, FIG. 2B shows the structure of data from the CRT controller, and FIG. 2C shows data specifying an address to the character generator. FIG. 3 is a diagram showing an example of a pattern of font data stored in a character generator in the device. 1 ... CPU, 2 ... Data writing means, 3 ... CRT controller, 4 ... Code buffer, 5 ... Character generator, 6 ... Selector, 7 ... Register, 8 ... First display bus, 9 ... Second display bus.

Claims (1)

(57) [Claims] A character generator capable of storing a plurality of fonts having different numbers of dots in a memory area indicated by the same character code, and the number of dots stored in the character generator based on selection of a character generator read bit. Selects a different font and outputs an enable signal to a register corresponding to the font; and a selector output from the character generator in response to switching of bits in a line count address output to the character generator. A register (7) for latching the font of the desired dot and receiving and outputting an enable signal.