Display memory with write inhibit signal for transparent foreground pixel codes

摘要

A computer is connected to a display device having a display memory system that is updated by the computer. The computer selects a pattern to be displayed and a screen location at which the selected pattern is to be displayed. A display subroutine effects fetching of a byte of pattern data for the selected pattern from a dedicated memory. The fetched pattern data includes pixel codes that indicate whether corresponding pixels of the selected pattern are "transparent" or darkened. The display subroutine then transmits the pixel codes to the display memory system. The display memory system includes circuitry that detects whether each transmitted pixel code represents a transparent pixel. If it does, the circuitry inhibits writing of that pixel code into a storage portion of the display memory system. The circuitry also enables writing of non-transparent pixel codes into the storage portion of the display memory system.