Abstract: A system in which several colors of the spectrum are selectable to be displayed having common polarity and with high contrast against a black background, utilizing liquid crystal cells along with linear and color polarizers disposed along an optical axis so that comparable results in either reflective or transmissive modes are achieved, with appropriate light sources.

Abstract: A bi-directional interface circuit which functions as an output driver to drive a corresponding communication data bus in response to the output of an associated microcomputer and as an input buffer to communicate data from the associated data bus to the microcomputer, wherein such input and output data to and from the microcomputer is communicated to a single port on the microcomputer. The bi-directional interface circuit is controlled by sensing the impedance condition existing on the input/output port of the microcomputer and correspondingly switches to either its output driver mode or input buffer mode.

Abstract: A graphics system for a raster scan CRT implements a light pen tracked by a cursor. Hits corresponding to the cursor are distinguished from those corresponding to background data by a selective interlacing technique. A threshold level shifting technique providing accurate measurement of a horizontal component of the cursor allows accurate prediction of the location of the center of the field of view during the next frame.