Enhanced video graphics controller

摘要

An enhanced video graphics controller for converting digital signals to a video signal is described. The controller is capable of displaying composite or analog RGB colors as well as providing shades of grey on monochrome displays. The processing of graphics information includes arranging 256 colors into 16 palettes of 16 colors each and is stored in a first memory. Pointers are assigned to each scan line of a frame of a display and these pointers are also stored in the first memory. Data fields which represent bit mapped video data are also stored in the first memory. For each scan line, a corresponding pointer is selected and this pointer selects one of the palettes to be loaded into a second memory. Then data field for that scan line address the second memory to provide color to the stored video data. The video controller is also capable of operating in several optional modes which include fill-in and dithering modes, as well as providing interrupts to update previous scan line information during the display cycle. Further, the controller is capable of enhancing existing displays by providing text and background color as well as providing a color border around the display.