Cathode ray tube controller

Abstract

A cathode ray tube controller provides character cell mapping of the entire cathode ray tube screen, including the blanked margins. This mapping permits video control signals, such as sync signals, blanking signals, retrace signals, etc., as well as character address designations, to be generated from a single ROM in each of the vertical and horizontal directions on the cathode ray tube screen. A horizontal character counter divides the cathode ray tube screen, including the blanked margin areas, into an integral number of character widths. This counter is used to address a read only member which provides, at its output, the horizontal character addressing in the non-blanked area of the cathode ray tube screen, as well as video control signals, including blanking signals, sync signals, etc. A vertical counter, similar to the horizontal counter, divides the entire cathode ray tube screen vertically, including the blanked areas, into a discrete number of character heights. Its output addresses a read only memory which provides both line address signals and vertical video control signals, such as sync signals and blanking signals. The system significantly reduces the amount of logic required to generate video control signals and addressing signals for the refresh memory. Partial screen scrolling is accomplished by duplicating the y axis read only memory to effectively animate the video screen using plural scroll images.

Dependencies are inferred from the claim text.