Digital character display

Abstract

A dual mode raster scanned character display system has a text mode of operation in which characters having a first matrix size are displayed on a CRT screen and a high resolution mode of operation in which display information is bit mapped on the CRT screen. Programmable font characters are stored in a memory and are accessed by controller characters generated in response to display requests supplied by an associated information source, such as a computer or a keyboard. Each controller character includes a special screen attribute multi-bit portion which is used to modify the font characters when coupled to a video signal generator unit to display reverse video, provide underline or strike through, specify one of two fixed intensities, suppress the character or provide a software function, such as CURSOR. In text mode, each character block has a fixed size appropriate to alphanumeric character generation, i.e. ten columns by sixteen rows; in high resolution mode of operation, each character block has a size appropriate to high resolution bit mapped graphic display, i.e. sixteen columns by sixteen rows. Both display and brightness are controlled by 3 bit digital characters supplied from the keyboard, the digital characters being converted from digital-to-analog form and used to control the brightness signal and the contrast signal level. The font characters are programmable from the associated information source, i.e. the computer.