Abstract: A method differentiates simultaneous and sequential key strokes by detecting simultaneous key strokes if two keys are pushed within a judging time T.sub.L. The method includes the steps of (a) measuring a first time T.sub.1 from a time when a first key is pushed to a time when a second key is pushed, and a second time T.sub.2 from the time when the second key is pushed to a time when one of the first and second keys is released, (b) comparing the first and second times T.sub.1 and T.sub.2 with an arbitrary threshold function T.sub.C which is set within the judging time T.sub.L, and (c) differentiating whether key strokes of the first and second keys are simultaneous or sequential based on a comparison result of the step (b).

Abstract: A video display control system displays a video image composed of a plurality of display elements on a screen of a video display unit. The system comprises a memory (VRAM) for storing a plurality of color codes each representing at least one display element and a video display controller (VDP). The VDP comprises a mode register for selecting one of normal display and transparency processing modes, display processing circuit for reading the color codes from the VRAM, a backdrop color register for storing a color code such as one representing a backdrop color, a detection circuit for detecting a predetermined color code from the color codes read by the display processing circuit, and a selector controlled by an output of the detection circuit. In the normal display mode, the selector outputs all color codes read by the display processing circuit to the display unit.