JP2619648B2 - Color image display control device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a color image display control device, and more particularly to a color image display control device connected to a central processing unit and a display control device and controlled by the two devices. Related to the device.

[Conventional technology]

In recent years, display control devices (video display controller devices, controlled by a central processing unit (hereinafter referred to as CPU),
Many presentations have been made on an image display control device controlled by VDC), and a system in which these are integrated into one system.

FIG. 4 is a block diagram showing an image display control device. In FIG. 4, reference numeral 10 denotes a CPU, 40 denotes a color image display control device, and 41 denotes an interface circuit, which is connected to a data line supplied from the CPU. Connected to 45 color palettes that can be rewritten.
In addition, the color palette includes read / write signal R / W and
It is controlled by the image display control signal ▲ ▼. 20 is VD
C, which is supplied to a flip-flop 46 (hereinafter referred to as F / F). The address of the color palette is selected from the output of the address register 43 and the F / F output of 46. The output of the selector circuit is connected. The RGB color data output from the color palette is connected to 47 F / Fs, and further connected to 48 F / Fs. 48 F
The RGB color data output from / F is supplied to 30 CRT displays through 49 D / A conversion circuits. The TV synchronization signal SYNC generated by the timing generation circuit 42 by the external basic clock input from the OSC is supplied to the CRT display device, and is used as the reference synchronization of the image display control device.
Are connected to F / F clock inputs 46 and 47 and an AND gate 50, and the output of the AND gate 50 is connected to a clock input of 48 F / Fs. This CLK has a period obtained by dividing a horizontal display period on a CRT display by the number of dots to be displayed, and supplies a clock signal which is a unit of an operation cycle. RGB color data is synchronized with this dot clock.
It is to be output to an RT display, and in internal operation, data is shifted in sequence in synchronization with this clock.

[Problems to be solved by the invention]

In the above-described conventional image display control device, the CPU accesses or writes to the color palette in a period other than the screen display period (for example, a horizontal or vertical blanking period), and the image is synchronized with the access. Display control signal ▲
▼ had changed. However, in the above-mentioned conventional circuit, since the internal data is shifted in synchronization with the dot clock, the access from the CPU ends, and ▲ ▼ changes to V
When reading the color palette from DC starts, VD
The color data corresponding to the color code supplied from C is not output as it is, the final color data written from the CPU remains in the 48 F / F, the color data is displayed on the screen, and the overscan When I went, it was flickering outside the image display.

The present invention solves such a problem, and outputs the color code from the VDC as accurate RGB color data when the access from the CPU to the color palette is switched from the CPU to the VDC during periods other than the display screen. It is another object of the present invention to provide a color image display control device with no flicker.

[Means for solving the problem]

In the color image display control device of the present invention, the color code of each dot for performing color display on the screen is supplied from the display control device, the color code is supplied in synchronization with the dot clock signal, and the color code corresponding to the color code is supplied. Storage means for switching the read operation or write operation of the RGB color data based on the control signal, and the RGB color data read from the storage means in synchronization with the dot clock signal. A color image display control device having a holding unit for holding, and supplying an output of the holding unit to a display device, wherein the control signal is converted to RGB color data corresponding to a color code supplied from the display control device. And a delay means for outputting a delay signal until the signal is supplied to the holding means, and holding the holding means based on the delay signal. When the operation of the storage unit is switched from the writing operation to the reading operation based on the control signal, the holding control unit is supplied from the display control device. Until the RGB color data corresponding to the color code is supplied to the holding unit, the holding unit holds the RGB color data corresponding to the color code supplied from the display control device. I do.

[Action]

The present invention, by providing a delay circuit for the control signal ▲ ▼ supplied from the central processing unit to the image display control device, allows access from the CPU to access to VDC to be switched during a period other than the screen display period when switching to VDC. Until the RGB color data corresponding to the VDC color code is output, the flicker can be eliminated because the RGB color data is not output by access from the CPU.

〔Example〕

Hereinafter, the present invention will be described based on examples. First
The figure is a block diagram showing the system in the present invention,
A control signal ▼ supplied from the central controller to the image display controller is connected to 50 AND gates via 60 delay circuits. FIG. 2 is a circuit diagram showing an embodiment as 60 delay circuits. 61 and 62 are reset D-type flip-flops; 63, 64 and 65 are NAND gates;
6, 67 and 68 are inverter gates. 61, 62, 63, 6
7, 68 constitute a ternary counter, and 64, 65 constitute a latch circuit. The dot clock CLK is input as a counter clock, ▲ is connected to the reset signal input of the counter and the latch, and the output of the counter is connected to the set signal input of the latch.

FIG. 3 is a timing waveform showing a data flow for explaining the delay circuit of FIG. During the screen display period,
Although RGB color data is output in synchronization with the dot clock, when rewriting the color palette during periods other than the screen display period, ▲ ▼ is set to “Low” asynchronously with CLK.
Level (take data on CPU side with ▲ ▼)
Then, the address and data of the color palette are transferred from the CPU. At this time, naturally, the 44 selectors select the address register, and the color code from VDC is not selected. ▲ ▼ becomes “High” level, and the selector selects the VDC color code. At this time, as apparent from FIG. 3, the output of the AND gate 50, that is, the clock input of the F / F48 is ▲ ▼ For at least 2 cycles of the dot clock after the signal has changed to “Low”, it remains at “Low” for a dummy cycle, and the 48 F / F
Keeps and outputs data before CPU access. Then, the dummy cycle ends, and the color data output from the color palette corresponding to the color code from VDC is output. As a result, there is no flicker caused by displaying the color data as it is by accessing the CPU.

〔The invention's effect〕

As described above, according to the present invention, the color image display control device of the present invention is configured such that a color code of each dot for performing color display on a screen is supplied from the display control device, and the color code is used as a dot clock signal. Supplied synchronously,
Store the RGB color data corresponding to the color code,
A storage unit configured to switch a read operation or a write operation of the RGB color data based on a control signal; and a holding unit that holds the RGB color data read from the storage unit in synchronization with the dot clock signal. ,
A color image display control device for supplying an output of the holding unit to a display device, wherein the control signal is transmitted until RGB color data corresponding to a color code supplied from the display control device is supplied to the holding unit. Delay means for delaying and outputting a delay signal, and holding control means for controlling holding of the holding means based on the delay signal, wherein the writing operation is performed from the writing operation to the reading operation based on the control signal. When the operation of the storage unit is switched, the holding control unit supplies the RGB color data corresponding to the color code supplied from the display control device from the display control device until the RGB color data is supplied to the holding unit. Since the holding means holds the RGB color data corresponding to the color code to be written, when switching from writing to reading, the RGB color data corresponding to the color code supplied from the control device will be supplied to the holding unit, and at the time of the switching, for example, the screen will be erased, or the written color data will be output as it is. Is prevented and screen flicker is eliminated. In particular, in an image display control device having a configuration in which data is processed while shifting data in synchronization with a dot clock as in the present invention, from supply of a color code to output of color data is performed by one clock signal. Since there is no need to perform sequential processing using multiple clocks in a so-called pipeline system, a low-speed storage device used as a color palette is sufficient, and the entire display control device does not need to be a high-speed device. Therefore, flicker can be prevented even with an inexpensive display device such as a television. Then, in the case where the screen is to be overscanned and used in a period other than the screen display period, flickering that occurs when switching from CPU access to VDC access can be prevented using a simple delay circuit,
A smooth screen can be obtained even during periods other than the screen display period.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a system configuration including a color image display control device of the present invention. FIG. 2 is a configuration circuit diagram showing a delay circuit constituting the image display control device shown in FIG. FIG. 3 is a timing waveform chart for explaining the operation of the delay circuit of FIG. FIG. 4 is a block diagram showing a system configuration including a conventional color image display control device. 10 Central processing unit (CPU), 20 Display control unit (VD
C: video display controller), 30 CRT display, 40 image display control device, 41 interface circuit, 42 timing generator circuit, 43 address register circuit, 44 selector circuit, 45 Color palette, 46, 47, 48, 61, 62 D flip-flop, 49 D / A converter circuit, 50 AND gate, 60
... delay circuits, 63, 64, 65 ... NAND gates, 66, 67, 68 ...
... Inverter circuit.

Claims (1)

(57) [Claims] 1. A color code of each dot for performing color display on a screen is supplied from a display control device, the color code is supplied in synchronization with a dot clock signal, and RGB color data corresponding to the color code is supplied. Storage means for storing and switching between read operation or write operation of the RGB color data based on a control signal; and holding means for holding the RGB color data read from the storage means in synchronization with the dot clock signal. A color image display control device for supplying an output of the holding unit to a display device, wherein the control signal is transmitted to the holding unit by RGB color data corresponding to a color code supplied from the display control device. Delay means for delaying until supplied and outputting a delay signal; holding control for controlling holding of the holding means based on the delay signal When the operation of the storage unit is switched from the writing operation to the reading operation based on the control signal, the holding control unit corresponds to a color code supplied from the display control device. Color image display control, wherein the holding means holds RGB color data corresponding to the color code supplied from the display control device until the supplied RGB color data is supplied to the holding means. apparatus.