Display controller

Abstract

In an image displaying field where there is a tendency which will increase the data to be handled in accordance with the high integration of a display device, a CRT controller according to the present invention improves the superposed display and the responsiveness of the display and drawing operations by dividing a unit clock into a predetermined number to function with high speed and a multifunction display. When image data are to be inputted or outputted from a refresh memory corresponding to a display frame, the memory content and the display address are assigned at a ratio of 1:n to effect the processings in parallel. As a result, the time period utilized by the display cycle of the prior art can be assigned to the drawing operation so that the processing can be speeded up while making it easier than the prior art to effect the superposed display of letters, symbols and drawings. The resultant effect is that it is unnecessary to increase the number of refresh memories corresponding to the displayed frame and that the external parts can be simplified to contribute to the improvement in the reliability.

Dependencies are inferred from the claim text.