JPH0462590B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a CRT display control circuit used in electronic equipment.

Conventional configuration and its problems In recent years, CRT display control circuits have played an important role in word processors. In particular, devices that handle German, Spanish, etc. are required to display symbols such as u¨'a in addition to the usual alpha alphabet.

A conventional CRT display control circuit will be explained below.

FIG. 1 shows a conventional CRT display control circuit. In the figure, a character code memory 1 outputs a character code corresponding to a refresh address. A character pattern generation memory (hereinafter abbreviated as CG) 2 reads a display pattern from an address specified by the character code and writes it into a shift register 3.

In order to display characters and symbols as shown in Figure 2 using the above method, all possible combinations of characters and symbols must be stored in the CG.
However, this method is not feasible with limited CG capacity. On the other hand, as a solution, as shown in Figure 3, the output of the character code memory 11 can be changed to
One possible method is to connect the symbol code memory 12 to the symbol CG14 to obtain the character pattern, and then connect the output of the symbol code memory 12 to the symbol CG14 to obtain the symbol pattern, but in this case, at least one extra CG is required, and the CG
Since these are expensive, there was a problem that this led to an increase in costs.

OBJECT OF THE INVENTION The present invention overcomes the above-mentioned conventional drawbacks.
To provide a CRT display control circuit capable of independently specifying a display character and a symbol to be added in a pattern generation memory and displaying them at the same place without providing an extra character pattern in the pattern generation memory. The purpose is to

Structure of the Invention The present invention includes a selector that switches between a character code corresponding to a character to be displayed and a symbol code corresponding to a symbol to be added, and a pattern generation memory having areas for storing a character pattern and a symbol pattern in one character area. By providing this, it is possible to independently designate the display character and the symbol to be added in the pattern generation memory when displaying one character.

DESCRIPTION OF THE EMBODIMENTS FIG. 4 shows a block diagram of a CRT display control circuit in one embodiment of the present invention, and FIG. 5 shows the configuration of the CG 24 used in FIG. 4.

Character code memory 21 and symbol code memory 22
The data from is selected by the selector 23 and then input to the character symbol CG 24 having the structure shown in FIG. The output of the character symbol CG24 is parallel-to-serial converted by the shift register 25 to become a video signal.

The operation of the CRT control circuit of this embodiment configured as described above will be explained below.

The character pattern is read out from the CG 24 by sequentially counting up the row address for a designated code and outputting the data at that address line by line. The row address is externally designated by 4-bit parallel format data (RA ₀ , RA ₁ , RA ₂ , RA ₃ ).
In this embodiment, the upper four lines of the one-character display area are the symbol display area, while the remaining nine lower lines are the character display area. When reading a symbol pattern, when data in the upper four rows, that is, the symbol display area, is being read, the upper two bits of the row address, that is, RA ₂ and RA ₃ , are always "0", so RA ₂ and RA ₃ are The AND output indicates which data from the symbol display area or the character display area is being output at that time, and this AND output is used as a switching signal to the selector 23. On the other hand, the selector 23 is configured to select the output of the character code memory 21 when the input select signal is "1", and to select the output of the symbol code memory 22 when the input select signal is "0". has been done. Therefore, when RA ₂ and RA ₃ are both "0", that is, when the output of the AND circuit is 1, the selector 23 selects the output of the character code memory 21 and adds it to the CG 24, and also selects the output of the character code memory ₂₁ and adds it to the CG ₂₄ . When either one is "1", that is, when the output of the AND circuit is 0, the selector 23 selects the output of the symbol code memory 22. In this way, when outputting 13 lines of data for one character from the CG24, the symbol code is input into the CG24 in the first half, the selector 23 is switched in the middle, and the second half is output by inputting the symbol code into the CG24.
By configuring the CG 24 to input character codes, even if the same character code is specified and the same code is output from the code memory 21, it is possible to input symbol codes that correspond to the character codes and differ from each other. By outputting from the symbol code memory 22, multiple types of symbols can be added to one character using multiple types of other symbol patterns in the CG 24 and displayed. For example, in the case shown in Figure 5, if you output code 0 as the character code and code 0 as the symbol code from memory and perform the display operation, the sentence "a¨" will be displayed as is, but the character code If a display operation is performed by outputting the code 0 as the symbol code and the code 1 as the symbol code from the memory, the character "a〓" will be displayed. Also, if you specify code 0 as the character code, and specify a code for a character pattern that does not include a symbol or a code that indicates an area where no character pattern is set, such as "e" as the symbol code, you can The part is not displayed, but the letter "a" is displayed.

As described above, according to this embodiment, even though there is only one CG, the functions of two CGs can be provided by inputting a code according to the display area.

In the embodiment, two patterns of characters and symbols are specified, but the present invention can also be applied to three or more patterns to obtain the desired effect.

Effects of the Invention As described above, the present invention provides a pattern generation memory including a first area for storing a character pattern in one character area and a second area for storing a symbol pattern, and a character code and a character code for characters to be displayed. A selector is provided to switch a symbol code corresponding to the symbol to be added and provide it to the pattern generation memory, and when reading a character pattern from the pattern generation memory, either the first area or the second area is specified. By configuring the selector to be controlled based on the identification data, data can be read from the first area of the pattern generation memory and from the second area during the character display operation. You can switch the code specified when reading data, so if you specify the character code when reading data from the first area and the symbol code when reading data from the second area, one character It is possible to specify by symbol code whether to display with or without a symbol, and what kind of symbol to attach to one character, and the pattern can already be generated without creating an extra character pattern. By using the symbol patterns provided in the memory, it is possible to add and display a plurality of types of symbols to one character.

[Brief explanation of the drawing]

Figure 1 is a block diagram of a conventional CRT display control circuit, Figure 2 is a diagram showing the contents of the CG used in Figure 1, Figure 3 is a block diagram of a CRT display control circuit using two CGs, FIG. 4 is a block diagram of a CRT display control circuit according to an embodiment of the present invention, and FIG. 5 is a diagram showing the configuration of a CG used in the circuit. 21...Character code memory, 22...Symbol code memory, 24...Character symbol CG, 25...Shift register.

Claims (1)

[Claims] 1 A pattern generation memory provided with a plurality of character pattern storage areas corresponding to code numbers, and comprising a first area for storing character patterns in one character area and a second area for storing symbol patterns. , a selector that switches between a code number corresponding to a character to be displayed and a code number indicating an area in which a symbol pattern to be added to the character to be displayed is stored and supplies it to the pattern generation memory; The device is characterized by having means for identifying whether the signal is being read from the first area or the second area and controlling the selector based on the result. CRT display control circuit.