PERSONAL COMPUTER APPARATUS FOR HOLDING AND MODIFYING VIDEO OUTPUT SIGNALS

A computer that provides data to a video display using a bitmap display memory organization and bitplane addressing. Separate control is provided for two bitplane backgrounds and for eight reusable and easily movable sprites. Additional logic allows for dynamically-controllable interobject priority and collision detection among data in each of the bitplane backgrounds and sprites. A coprocessor provides for video beam-synchronized changes to data in registers, freeing the main processor for general purpose computing tasks. A block image transferer is provided to rapidly copy data in large blocks from one memory location to another. In hold-and-modify mode, color output circuitry holds the values for a previously displayed pixel while bitplane data modifies those values, allowing for simultaneous display of a greatly increased number of colors.