Abstract

By selecting the starting time of the display readout of a pel buffer raster generation, the pel data is mapped to a display screen with an arbitrary displacement with respect to the screen for relocation or scrolling of the pel image on the screen. To compensate for non-congruency between the pel data window and screen viewport definitions and to provide scrolling on a pel basis, the positioning of the window on the screen includes fine adjustment achieved by a determinable delay between the scanning of the buffer and the generation of the screen raster. The display circuits include means to extend the window background to fill in gaps between the edges of a window of pel data chosen to be displayed and a larger screen viewport in which it is to be displayed. System read/write access times to the buffer are interleaved with and synchronized to the data fetch times of the display.