Abstract: A device controls in real time the assembly of data for a bit map scanning device, such as a laser printer, under supervisory control of a host processor. The image data words are stored in a source memory and assembled in a video buffer, and automatically scanned out to the scanning device. The host processor generates a simplified set of control words that defines graphics, text and layout of the page to be assembled. A raster interface synchronizes the output of the assembled data with the scanning device. Three basic modes are supported: (1) dispatch mode, (2) font read/write mode, and (3) graphics load mode. The dispatch mode is the normal operational mode which provides for dispatching data from a source memory location to the video memory and for supplying data from the video memory out to the raster printer. The font read/write mode gives the host the ability to read/write font or graphics data from/to the source memory or the video memory.