| 摘要 |
Electronic circuitry for generation of graphics images on a computer display screen is disclosed which allows graphics capability to be added or retrofitted to computers having standard video display character generation circuitry. The graphics circuitry receives address, data and control signals from the normal computer peripheral bus. Address signals received by the graphics circuitry are interpreted as command signals and, in accordance with the command signals, data present on the computer peripheral data bus is interpreted either as graphics data to be written in a random access graphics memory or as an address location for such data in the memory. The graphics circuitry normally operates asynchronously with respect to the computer under control of the character clock generated by the character generation circuitry. Proper synchronization with computer operation is achieved by using wait commands which cause the computer circuitry to cease processing temporarily while write or read operations are being processed by the graphics circuitry. In addition, special circuitry is provided which allows the graphics circuitry to automatically increment and decrement address information stored within the circuitry.
|
