Circuitry for controlling a CRT beam

摘要

A CRT beam control apparatus wherein a microprocessor drives the CRT beam for controlling the beam characteristics, including writing speed, slope, position and intensity. The apparatus includes a single digital-to-analog converter supplying sample-and-hold circuitry through a selector and further includes a pair of active integrator circuits switchable to connect the output of the digital-to-analog converter or sample-and-hold circuits. The microprocessor is operative to provide digital words to the DAC representative of the differential X and Y values of a line segment to be drawn. The analog representations of these digital words are coupled to the integrators. The outputs of the active integrators provide the deflection signals causing deflection of the CRT beam. The apparatus is particularly adapted to drawing a series of connected line segments, due to the integrator operation. A line segment length may be scaled simply by varying the time interval that the analog signals are applied to the integrators, while the writing speed remains constant. The apparatus is also adaptive to display a pseudo-raster scan field.