Display control device

Abstract

When the horizontal period is less than a lower limit threshold value in a state that an LCD panel is driven in an SVGA mode, a mode judging circuit judges the resolution of an image signal as VGA. When the horizontal period is above an upper limit threshold value in a state that the LCD panel is driven in a VGA mode, the mode judging circuit judges the resolution of the image signal as SVGA. Even when frequency modulation is applied to the input signal, the modulation is absorbed by the width between the lower limit threshold value and the upper limit threshold value, whereby the resolution of the image signal can be reliably judged. A control signal generating circuit controls the timing of driving the LCD panel in accordance with the resolution, whereby image signals of a plurality of different resolutions can be reliably displayed on the LCD panel.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

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

FIG. 2 is a graph showing a judgment reference of the judging means of the display control device,

FIG. 3 is a timing chart showing the operation corresponding to a first resolution of the display control device,

FIG. 4 is a timing chart showing the operation corresponding to a second resolution of the display control device,

FIG. 5 is a graph showing clock numbers of the first resolution and the second resolution of the display control device, and

FIG. 6 is a block diagram showing a graphic system having the display control device.

Claims

1. A display control device comprising: detecting means for detecting a horizontal period of a synchronous signal contained in an input signal from an external source;judging means for judging the resolution corresponding to an image signal contained in the input signal on the basis of the horizontal period detected by the detecting means; andcontrol means for controlling the timing of a display device in connection with the resolution judged by the judging means, whereinwhen the horizontal period is less than a predetermined lower limit threshold value in a state that the display device is driven in connection with a first resolution, the judging means judges the resolution of the image signal as a second resolution lower than the first resolution, and when the horizontal period is above a predetermined upper limit threshold value larger than the lower limit threshold value in a state that the display device is driven in connection with the second resolution, the judging means judges the resolution of the image signal as the first resolution.

2. The display control device according to claim 1, wherein the width between the lower limit threshold value and the upper limit threshold value is set to be larger than the variation width of the horizontal period of the synchronous signal of the input signal.

3. The display control device according to claim 1, wherein the lower limit threshold value is larger than a numerical value achieved by adding the horizontal display period corresponding to the first resolution with a preset predetermined value.

4. The display control device according to claim 1, wherein the judging means judges the resolution of the image signal on the basis of the horizontal period of the synchronous signal corresponding to a prescribed line of the image signal of the input signal.

5. The display control device according to claim 1, wherein the judging means judges the resolution of the image signal on the basis of the horizontal period of the synchronous signal corresponding to all the lines in one frame of the image signal of the input signal.