JPH0336593A - Screen display device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] [4! TECHNICAL FIELD The present invention relates to a screen display device, and more particularly to a screen display device incorporating a rewritable character ROM that facilitates user program development.

[Conventional technology]

FIG. 3 is a block diagram showing the configuration of an embodiment of a conventional screen display device.

1 is a RAM (hereinafter referred to as CRTRAM) that stores part of the address for one character of a character ROM (described later); 2 is n
3 is a character ROM address generation circuit, 4 is an m counter, 5 is a character ROM, and 6 is a shift register.

Next, the operation will be explained. Using the address generated from n counter 2, select the type of character at each address corresponding to the display order of CRTRAM1, and select the type of character at each address corresponding to the display order of CRTRAM1.
From the data of , and the data of m counter 4, character ROM3
An address for decoding the character ROM 5 is generated by the address generation circuit. This 1-bit data from the character ROM 3 is input to the shift register 6 and output from the output terminal.

[Problem to be solved by the invention]

Since the character ROM 3 of the screen display device is constituted by a mask ROM, it takes a lot of time and cost for the user to create a new program, and there is a problem that program development is not easy.

This invention was made in order to solve the above-mentioned problems, and by configuring the character ROM 3 with a rewritable ROM and a mask ROM, the user can easily develop programs, and furthermore, the ROM 3 has a built-in rewritable ROM. The purpose is to make testing easier.

[Means to solve the problem]

In order to solve the above problems, in the present invention, a ROM in which the character RQM can be rewritten and a part of the address for one character are set so that the polarity of at least one bit among adjacent bits is different. Mask ROM
comprising a selection signal generating means for selecting one of the above areas, and a selection circuit for receiving the selection signal of the means and selecting either the rewritable ROM area or the mask ROM area. It is designed to be configured as follows.

[Effect]

According to this invention, a ROM in which a character ROM can be rewritten
By configuring it with a mask ROM and a mask ROM, it is possible to facilitate the user's program development. In addition, some addresses of one character of the mask R□M are set such that at least one of the adjacent bits has a different polarity, for example, a C that selects a character ROM.
If the R'f' RAM is 8 bits, the CRTRAM data output line names are b7 to bO, and the layout is as shown in Figure 2, the fixed ROM area of the character ROM is ' A AHo
Or, '55H' shall be included. Therefore, CRTR
At least one of the AMR-ta is C due to the chip layout.
Adjacent lines of the RTRAM data output lines will contain data sets of different polarities.

Therefore, during testing, by selecting and checking the characters stored in the mask ROM, you can test the contents of the mask ROM and at the same time check whether adjacent lines of the CRTRAM data output line are short-circuited. can be tested.

〔Example〕

FIG. 1 is a block diagram showing one embodiment of the present invention, and numerals 1 to 6 are equivalent to those in the conventional device.

In the figure, 5 is a character ROM, which is a rewritable ROM.
It is composed of an M area 5a and a mask ROM area 5b.

7 is a ROM area selection circuit, and 8 is a ROM area selection signal generating means.

Next, the operation will be explained. The type of character is selected at each address corresponding to the display order of CRTRAM 1 according to the address generated from n counter 2, and the character type is selected at each address corresponding to the display order of CRTRAM 1.
, and the data of the m counter 4, the character ROM address generation circuit 3 generates an address for decoding the character ROM 5.

Based on this address l) ROM area area selection circuit which receives the signal from the ROM area selection signal generation means 8 reads out the contents of the character ROM 5 in the selected area, and inputs the e-bit data from the character ROM 5 to the shift register 6. and output from the output terminal.

Also, when testing, mask ROM5bll: By selecting and confirming the stored characters, the mask ROM
5b address selection CR'rRAM data (
At least one of the data sets includes a data set in which adjacent lines of the CRTRAM data output lines have different polarities due to the chip layout. Test to see if it is.

〔Effect of the invention〕

As described above, according to the present invention, the character ROM is composed of a rewritable ROM and a mask ROM, and one of the ROMs can be selected by the ROM area selection +111 path, and the address of the mask ROM is selected by the CRTRA.
MR-data (at least one is CR due to chip layout)
Adjacent lines of the TRAM data output line contain data sets with different polarities, so we provide a screen display device with a rewritable character ROM that facilitates user program development, and we test it when shipping blanks. give you the means to do so. Further, it is possible to perform tests that do not depend on the user ROM, and it is possible to provide a screen display device having a high quality rewritable character ROM at a low cost and more quickly.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the entire screen display device according to an embodiment of the present invention, FIG. 2 is a layout diagram showing an example of CRTRAM data lines, and FIG. 1143 is a block diagram showing the overall structure of a conventional screen display device. FIG. In the figure, 1 is CRTRAM, 2 is n counter, 3
is a character ROM address generation circuit, 4 is an m counter, 5 is a character ROM, 5m is a rewritable ROM area, 5b is a mask ROM area, 6 is a shift register, 7 is a ROM area selection circuit, 8 is a ROM area selection signal generation It is a means. In each figure, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] A screen display device that reads the contents of a storage device storing contents to be displayed in response to a command to be displayed on a screen and outputs the required contents to be displayed, the storage device comprising: a rewritable ROM area; It consists of a mask ROM area in which the polarity of at least one bit among adjacent bits is set to be different from the polarity of some of the addresses of characters, and a selection signal is generated to select either of the above two areas. A screen display device comprising: means; and a selection circuit for receiving a selection signal from the means and selecting either the rewritable ROM area or the mask ROM area.