JPH0225190B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an underline display circuit for a computer equipped with a text video RAM and a graphics video RAM and capable of displaying characters and graphics on the screen. .

(Prior Art) Recently, computers have been provided that are equipped with a video RAM for text and a video RAM for graphics, and are capable of displaying characters and graphics on a television screen.

(Problem to be Solved by the Invention) However, in this type of computer, in order to underline a character, it is necessary to rewrite the contents of the video RAM for text and the video RAM for graphics, and it is not easy to do so. I can't change the underline color.

(Means for Solving the Problems) In the present invention, the output of a text video RAM is converted to pattern data via a character generator, and this pattern data is converted to serial dot data by a shift register. A CRT controller that outputs a raster address consisting of an address corresponding to the number of rasters constituting one character and an address corresponding to the number of underline spaces, and an underline controller that determines whether or not to display an underline. The attribute video RAM that outputs the underline signal receives the underline signal, compares the raster address with a preset raster number, and when these values match, outputs an underline active signal and a text cut signal. The output of the shift register is cut off by the text cut signal, and the output of the shift register is cut off by the text cut signal, and the output of the attribute video RAM is cut off by the underline active signal.
The present invention relates to an underline display circuit in which an underline corresponding to color data specified by is displayed.

(Function) In addition to the signal indicating color data, for example, 1 bit is added to the attribute video RAM, and this 1 bit is allocated as an underline signal.

On the other hand, a raster address is obtained by adding an address corresponding to the number of underline spaces to an address corresponding to the number of rasters constituting one character.
When output from the CRT controller, a comparison circuit compares a preset raster number with the raster address, and when these values match, outputs an underline active signal and a text cut signal.

Then, the text cut signal cuts off the output of the shift register, and the underline active signal causes an underline with a color specified in the attribute video RAM to be displayed for each character.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing a text data output section, and the circuit surrounded by a broken line is an underline circuit 4. As shown in FIG.

The text video RAM 1 is controlled by the address specified by the CRT controller (not shown).
Output the character code to the character generator 2.

In the character generator 2, the character code sent from the text video RAM 1 is converted into pattern data to be actually displayed, and such pattern data is input to the shift register 3, where it is converted into serial dot text data. is converted to This dot text data is OR
Color data (blue,
3 AND gates 5 that take logical AND with red, green)
They are input to a, 5b, and 5c, respectively. In addition, this shift register 3 is controlled by a control signal _S1 output from an underline circuit 4, which will be described later.
Shift/Load is performed. That is, the control signal S ₁
If it is at "H" level, it will be a Shift command, and if it is at "L" level, it will be a Load command.

The attribute video RAM 7 is the CRT
Character attribute data is output using the address specified by the controller. The color data (blue, red, green) of this attribute data is inputted via the latch circuit 8 to the AND gates 5a, 5b, and 5c, respectively. An underline signal _S2 is assigned to one bit in the attribute data of a character, and when it is desired to display an underline on a specific character selected by the CRT controller, the attribute data indicating this character is The underline signal _S2 within is set to active ("H" level).

This underline signal _S2 and the raster address output from the CRT controller are input to the comparison circuit 4b. This raster address consists of an address corresponding to the number of rasters constituting one character and an address corresponding to the underline space.

The number of rasters is set in advance in the comparator circuit 4b, which takes in the underline signal _S2 and compares the raster address with the number of rasters if the underline signal _S2 is an active signal ("H" level). When both match, the underline active signal _S3 is activated (“H”).
level).

This underline active signal _S3 is
The data is input to the OR gate 4a, and the OR gate performs a logical sum with the text dot data output from the shift register 3. When the underline active signal _S3 is active ("H" level), the text dot data maintains the "H" level, so it is converted to the color specified by the color data in the attribute data and sent to the TV. Sent.

In addition, in this comparison circuit 4b, a text cut signal _S4 that prevents unnecessary character data from being displayed between the spaces provided above and below a character to display an underline corresponds to the underline signal _S2 . is output.

This text cut signal S ₄ is for text
The signal input to the negative logic NAND gate 4c together with the Shift/Load signal _S5 and output through this NAND gate becomes the control signal _S1 , and the text cut signal _S4 becomes an active signal ("H" level).
When , text data is not output.

The concrete circuit of this comparison circuit 4b is constructed as shown in FIG.

This circuit converts the font of one character into 8×8
This circuit is used in the case of dots, and consists of two inverters 13a and 13b and a negative logic AND gate 14, and the raster addresses are RAφ, RA1,
It consists of 4 bits, RA2 and RA3, and in addition to these 4 bits, 1 bit for an underline signal line is added, making a total of 5 bits of data input.
The lines RAφ, RA1, and RA2 are directly input to the negative logic AND gate 14, and the RA3 and underline signals _S2 are input to the inverters 13b and 13, respectively.
It is input to the negative logic AND gate 14 via a.

The text cut signal S ₄ is then taken from the input line of RA3, and the underline active signal S ₃ is taken from the negative logic AND gate 14.

At this time, displaying the underline requires that much space, so if you increase the space by two lines for the underline, the number of rasters required for one character is the 8 rasters required to display 8 bits vertically. In addition to 2 rasters, there are 10 rasters from φ to 9, and 4 bits are required for the raster address.

At this time, if you display an underline on the 8th raster [Figure 3 B], RAφ
= "L" level, RA1 = "L" level, RA2 =
When RA3 is at "L" level and RA3 is at "H" level, the underline active signal _S3 becomes active ("H" level). Also, in order to prevent text data from being output during the two-line space added for underlining, the text cut signal _S4 is set to be active ("H" level) when RA3 = "H" level. There is.

Therefore, when the raster address reaches "8", the underline active signal _S3 is
Become active and attribute video
An underline of the color specified in RAM7 is displayed.

(Effects of the Invention) As described above, according to the present invention, an underline can be displayed without the need to rewrite the contents of the video RAM for text or the video RAM for graphics. Also, attribute video
Since the underline signal is assigned to the RAM, it is possible to set whether or not to display an underline for each character, and the underline color can be easily changed for each character.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing the output section of a computer equipped with an underline display circuit according to the present invention, Fig. 2 is a circuit diagram illustrating a specific configuration of a comparison circuit, and Fig. 3A shows no underlining. FIG. 5B is a diagram illustrating an underlined state. 1... Video RAM for text, 3... Shift register, 4... Underline display circuit, 4b
...Comparison circuit, 7...Video for attribute
RAM.

Claims (1)

[Claims] 1. In a computer in which the output of a text video RAM is converted to pattern data via a character generator, and this pattern data is converted to serial dot data by a shift register, A CRT controller that outputs a raster address consisting of an address corresponding to the number of rasters and an address corresponding to the number of spaces for underlining, and an attribute for outputting an underline signal that determines whether or not to display an underline. a video RAM; and a comparison circuit that receives the underline signal, compares the raster address with a preset raster number, and outputs an underline active signal and a text cut signal when these values match. The output of the shift register is cut off in response to a text cut signal, and an underline corresponding to the color data specified by the attribute video RAM is displayed in response to an underline active signal. An underline display circuit characterized by: