Abstract: A raster scanned video display for high resolution graphics on to which a graphical cursor can be superimposed. Cursor data corresponding to the next raster line of the image is read out of a data store during the line blanking interval and stored in a fast memory. During scanning of that next raster line the cursor data is combined with the image data. By combining the cursor data with the image data in this way, on a line-by-line basis, storage space requirements in the fast memory are greatly reduced.

Abstract: Data processing system having a main processor system and a diagnostic unit. The main processor system may transmit messages selected by itself to the diagnostic unit. It does so by writing information to a predetermined location in a writable microprogram control store. The diagnostic unit loads the address of that location into a reference address register and sets an address comparison circuit to respond only to write accesses. The address comparison circuit then outputs a signal on a line when it detects equivalence between that address and the address used in the control store access, held in an address input register. The output signal acts as an interrupt signal for a microprocessor system which subsequently causes a halt circuit to halt execution of microinstructions in the main processor. It then causes a control circuit 76 to carry out a read access of the control store at the predetermined address, held in an address output register. The data output is received in a data output register.