Philips Electronics North America Corporation

Philips Electronics N.a. Corporation

Christopher Walsh

Michael J Schaffstein

A graphics controller produces a composite image through selecting between input image pixels, which are designated to be displayed in the same pixel location, by using a select function. The select function is computed on a pixel by pixel basis to provide a select signal that indicates which pixel should be chosen for display as the final composite image on the display screen. The select signal uses mixing key functions to determine which pixel should be passed. The results of these functions are output in the form of key codes. Key codes are combined by performing a logical AND operation between the key codes, and with a Raster OPeration (ROP) code. The ROP code designates which key code combinations are to be logically ORed together to provide an increased number of possible key combinations to determine the selection of the image to be displayed.

Graphics controller for forming a composite image

A video graphics controller (VGC) for communicating with a frame buffer memory and a display device includes a first-in, first-out (FIFO)-configured memory, a memory controller for communicating with the frame buffer memory and controlling the FIFO-configured memory, and read and write pointers for the FIFO-configured memory. A subtractor is coupled to the read and write pointers for generating a difference signal which is coupled to the memory controller, and the read pointer generates a read carrier signal which is provided to a lock detector along with an end-of-frame signal. The lock detector generates an output signal which is coupled to the memory controller in order to place the video graphics controller in a locked mode of operation if no read carry signal is generated during an inputting of an entire frame of information into the FIFO-configured memory, and in an unlocked mode of operation if a read carry signal is generated prior to the completion of the inputting of an entire frame of information.

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Arlington, MA, United States of America

Christopher Walsh