JPH0362095A - Character display control circuit - Google Patents

Abstract

PURPOSE:To allow the use of an arbitrary code system as a code for text displaying and to increase a processing speed by varying a method for forming the address of a font ROM from the text code. CONSTITUTION:An address is outputted from a display controller 1 to a text RAM 2 at the time of making the text display. The read out data is sent to a converting circuit 4, by which data is converted to the address of the font ROM 5 complying with the desired code body system in accordance with the value set in a mode register 3. The address of the front ROM is formed from a shift JIS code, JIS 2-byte code, etc., by the value set in the mode register in this way and, therefore, the need for the conversion by software is eliminated and the speed of processing is increased as compared to the system of using the single code.

Description

DETAILED DESCRIPTION OF THE INVENTION [Objective of the Invention (Field of Industrial Application) This invention relates to a character display control circuit suitable for use in a personal computer.

(Prior Art) Conventionally, in a personal computer having a display device capable of displaying text characters, the character code stored in the text RAM is a shift JIS code or a JIS 2-byte code (or other code). Two coding schemes are selected and used. For example, in a device that uses Shift JIS as the character code stored in text (text) RAM, if you try to input JIS 2-byte code, the software (or BiO
2) requires the operation of converting the 2-byte code into a shift JIS code and writing it into the text RAM.

(Problems to be Solved by the Invention) According to the conventional example, as described above, when displaying text using a code that is not supported by the hardware, conversion by software is required.
It had the disadvantage of slow processing speed.

This invention has been made in view of the above-mentioned drawbacks, and provides a character display in which an arbitrary code system can be used as a code for displaying text by making the method of generating a font ROM address from a text code variable. The purpose is to provide a control circuit.

[Structure of the Invention] (Means for Solving the Problems) The present invention provides a text RAM that stores text code data for text display and attribute data for setting display attributes, and a text RAM that stores text code data for displaying text and attribute data for setting display attributes, and a
A display controller that generates an address for l, a mode register that sets the type of text code to be used, and a font ROM that stores the font pattern of display characters by converting text code data based on the contents of the mode register. It is equipped with a code conversion circuit that converts into addresses, and a display signal generation circuit that generates display control signals based on font ROM output and attribute data.
It is characterized by variable conversion into addresses.

(Function) With the above configuration, when displaying text, the display controller outputs an address to the text RAM, and the code data read here is sent to the conversion circuit and set in the mode register. Based on the value, it is converted into a font ROM address according to the desired code system.

In this way, a mode register in which the conversion method is set and a code conversion circuit that converts the text code into a font ROM address based on the value set in this mode register are added to the conventional components of this type of character display device. By doing so, a character display control device that can use any code as a code for displaying text is realized. Depending on the value set in the mode register, the address of the font ROM can be generated from shift JIS code, JIS 2 byte, etc., which eliminates the need for conversion by software compared to systems that use a single code, increasing processing speed, etc. There is an effect.

(Example) Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the present invention.

In the figure, a display controller 1 generates addresses for the text RAM 2 and performs other display controls. 2 is a text RAM, and a CP (not shown)
Codes and attributes for character display are written and stored in U. 3 is a mode register in which the code conversion method is set by the CPU. 4 is a code conversion circuit, and based on the value set in mode register 3,
The code read from the text RAM 2 is converted into a desired font ROM address. Reference numeral 5 denotes a font ROM, which contains character patterns according to each code system. A display signal generation circuit 6 generates a display control signal for the display based on the data and attribute data of the font ROM 5.

The operation of the embodiment of the present invention will be described below with reference to FIG. 1 above.

When displaying text, the display controller 1 outputs an address to the text RAM 2,
Code and attribute data are read. The code data read from the text RAM 2 is sent to the code conversion circuit 4 and converted into an address for the font ROM 5 based on the value set in the mode register 3. In the display signal generation circuit 6, the font R
Pattern data and text R read from OM5
A display control signal is generated based on the attribute data read from AM2. The signal generated by the display signal generation circuit 6 is transmitted from a CRT, plasma, etc.
The signal is supplied to a display monitor (not shown).

For example, when the value set in mode register 3 is “0”, J
When the IS2 byte code is "1", it is assumed to be a shift JIS code, and if the character pattern "A" is stored at address N of the font ROM 5, the code conversion circuit 4 will write:
When the value of mode register 3 is “0”, the text code is 3021H, and when it is “1”, the text code is 88
At 9FH, conversion is performed such that the output becomes N (font ROM address).

[Effects of the Invention] As described above, according to the present invention, there is provided a text RAM that stores text code data for text display and attribute data for setting display attributes, and an address generation for the RAM when displaying. A display controller that performs the following operations, a mode register that sets the type of text code to be used, and an address of the font ROM containing the built-in font pattern of the displayed text code data based on the contents of this mode register. A code conversion circuit that converts the above font ROM into
and a display signal generation circuit that generates a display control signal based on the output and attribute data, and has a configuration in which the conversion from text code to font ROM address is variable depending on the value set in the mode register. This allows the font ROM address to be generated from shift JIS code, JI32 byte code, etc., depending on the value set in the mode register, eliminating the need for conversion by software and increasing processing speed compared to systems that use a single code. .

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... Display controller, 2... Text RAM, 3... Mode register, 4... Code conversion circuit, 5... Font ROM, 6... Display signal generation circuit.

Claims (1)

[Claims] A text RAM that stores text code data for text display and attribute data for setting display attributes, a display controller that generates an address for the RAM when displaying, and the type of text code to be used are set. A mode register, a code conversion circuit that converts text code data into the address of the font ROM containing the font pattern of display characters based on the contents of this mode register, and the output of the font ROM and attribute data. 1. A character display control circuit comprising: a display signal generation circuit for generating a display control signal; and a display signal generation circuit for generating a display control signal, the character display control circuit being characterized in that conversion from a text code to a font ROM address is made variable according to a value set in a mode register.