JPH06231269A - Display control device - Google Patents

Abstract

PURPOSE:To provide the display control device with a simple circuitry capable of specifying a clipping area. CONSTITUTION:In the display control device, the storage contents of VRAM is updated under the control of a CPU, and a picture is displayed on a display device according to the storage contents of the VRAM. It is equipped with a clipping area specification data table 21 storing the data specifying the clipping area by a VRAM space address and an AND gate 22 selectively masking a write request signal to the VRAM based on the data read from the table 21 with a drawing address sent from the CPU.

Description

Detailed Description of the Invention

[0001]

This invention relates to a central processing unit (CP).
The present invention relates to a display control device that updates the storage contents of a video memory (VRAM) under the control of U) and displays an image on a display device according to the storage contents of the VRAM.

[0002]

2. Description of the Related Art Various image processing systems require a so-called clipping function for setting a drawable area or a prohibited area on a display screen. Such clipping is performed by the CPU when writing character data in the VRAM, by comparing with a preset clipping boundary and controlling writing in the VRAM. FIG. 3 is an example of a display screen on which such drawing control is performed. The shaded area on the screen of the display object indicates the mask area in which drawing is prohibited. FIG. 4 shows an example of a conventional clipping control circuit. Conventionally, the drawing area is
The display space address is specified by a range surrounded by the start point coordinates and the end point coordinates, and it is determined whether the drawing address is included in the range.

[0003]

However, in the conventional method shown in FIG. 4, a conversion circuit for converting a drawing address into a display space address is necessary in order to specify a clipping area with a display space address. Further, in order to specify the clipping start point and the clipping end point on the X and Y addresses of the display space, four comparison circuits are required for one area designation. Moreover, the comparison circuit is complicated including the subtraction circuit. If a plurality of areas are to be designated at random, a plurality of circuits in FIG. 4 are required. On the other hand, it is conceivable that the CPU determines the clipping region to control the data transfer, but this is not preferable because the burden on the CPU becomes too heavy.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a display control device capable of designating a clipping area in an arbitrary form with a simple circuit configuration.

[0005]

According to the present invention, there is provided a display control device for updating a storage content of a video memory under the control of a central processing unit and displaying an image on a display device according to the storage content of the video memory. Control data storage means for storing data designating a clipping area by a memory space address of the video memory, and data for the video memory based on the data read from the control data storage means by a drawing address sent from a central processing unit. And a mask means for selectively masking the write request signal.

[0006]

In the present invention, the control data storage means for storing the data designating the clipping area corresponding to the VRAM space address is provided. At the time of drawing, the control data storage means is accessed by the drawing address to the VRAM, and the writing to the VRAM is controlled by the read data. That is, the write request signal (drawing command) to the VRAM is masked according to the data of the control data storage means, and the VRAM write enable signal is turned on and off. Therefore, in this invention,
There is no need for an address conversion circuit or a comparison circuit for comparing the drawing address sent from the CPU with the clipping area designation address. Moreover, according to the present invention, the clipping area can be designated in display dot units or character units, and drawing clipping of an arbitrary shape can be performed.

[0007]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration of a display control device according to an embodiment of the present invention. As shown in the figure, the display control device includes a CPU 1, a ROM 2 storing a control program,
A character ROM 3 storing character data, a video display processor (VDP) 4, a VRAM 5,
It has an attribute data RAM 6 and a CRT display device 7.
The VDP 4 has a timing control circuit 11, a write / read control circuit 12, a color palette 13, a D / A converter 14, and the like. VRAM 5 and attribute data RAM 6
Is provided outside VDP4 in this embodiment, but V
It may be inside DP4.

The CPU 1 generates display data (character name) and display position data according to a program stored in the ROM 2. In the case of this embodiment, the display position data is
It is data corresponding to the address of the VRAM 5. The write / read control circuit 12 has a CPU for the VRAM 5.
The display data is written to the VRAM address corresponding to the display position data sent from 1, the written data is read, and the read display data (character name)
The color code is transferred to the color palette 13 by referring to the character ROM 3 based on the above. V
Data is read from the RAM 5 by the timing control circuit 1
1 controls the timing so as to synchronize with the scanning of the CRT display device 7. The color code is converted into an RGB signal by the color palette 14, and this is converted into analog data by the D / A converter 14 to be converted into a CRT.
It is sent to the display device 7.

The attribute data RAM 6 stores various control data other than the character name, such as control data for modifying or changing the color code read from the character ROM 3 in accordance with the display screen. It is a memory. In the case of this embodiment, the attribute data RAM 6 is a clipping area designation data table for storing, in addition to the normal control data exemplified above, data for designating a clipping area in display dot units or character units corresponding to drawing addresses. Have.

FIG. 2 shows a portion related to the clipping area designation of this embodiment. The drawing address from the CPU 1 is sent to the VRAM 5 and also to the attribute data RAM 6, and as shown in the figure, the attribute data R
The clipping area designation data table 21 in AM6 is referred to. The AND gate 22 is a gate for turning on and off the write enable signal WE to the VRAM 5 by taking the product of the data read from the clipping area designation data table 21 and the drawing command. In other words, the AND gate 22 is a mask means for selectively masking the drawing command, and the W gate in FIG.
It is included in the / R control unit 12.

With such a configuration, the clipping area designation data table 21 is previously written with clipping area designation data for instructing drawing or prohibition in display dot units or character units. Then, at the time of drawing, the data of the clipping area designation data table 21 indicated by the drawing address is read, and the VR
Clipping can be performed by controlling the display data writing to the AM.

According to this embodiment, a complicated circuit for specifying the clipping area is not required unlike the prior art. In addition, it is possible to perform clipping of any shape, as well as to specify a plurality of discrete areas. In this embodiment, the VRAM 5 and the attribute data RAM 6 are provided separately, but they do not have to be provided separately and, for example, several bits in the image data stored in the VRAM may be used as the attribute data.

[0013]

As described above, according to the present invention,
By providing the control memory for designating the clipping region by the VRAM space address, it is possible to obtain the display control device capable of designating the clipping region of any shape with a simple circuit configuration.

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic configuration of a display control device according to an embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of a portion related to clipping region designation in FIG.

FIG. 3 is a diagram for explaining a clipping operation.

FIG. 4 is a configuration example of a conventional clip circuit.

[Explanation of symbols]

1 ... CPU, 2 ... ROM, 3 ... Character ROM, 4 ...
VDP, 5 ... VRAM, 6 ... Attribute data RAM, 7 ... C
RT display device, 11 ... Timing control circuit, 12 ... W /
R control circuit, 13 ... Color palette, 14 ... D / A converter, 21 ... Clipping area designation data table,
22 ... AND gate.

Claims (1)

[Claims] 1. A display control device for updating storage contents of a video memory under the control of a central processing unit and displaying an image on a display device according to the storage contents of the video memory, wherein a memory space address of the video memory is used. Control data storage means for storing data designating a clipping area; and a write request signal to the video memory selectively based on the data read from the control data storage means by a drawing address sent from the central processing unit. A display control device comprising: a masking unit for masking.