Abstract: A programmable interrupt controller (510) for a single interrupt architecture processor (518) includes a plurality of interrupt sources (502) each operable to generate an interrupt. A dynamically alterable interrupt mask (508) selectively blocks interrupt signals for the interrupt sources (502). Interrupts permitted by the dynamically alterable interrupt mask (508) are processed by an interrupt handler (500) for the single interrupt architecture processor (518) in order of priority. In addition, processing for a lower priority interrupt is interrupted in order to process a later received higher priority interrupt permitted by the dynamically alterable interrupt mask (508).

Abstract: A color video projection system (10) in which images of three separate colors (22,24,26) are separately projected to converge on a common region of the screen (20) is provided with automatic convergence control to ensure that three images are precisely superimposed upon each other. A test pattern of a number of pattern units (36,38) of an intensity (42,44,48) that varies over each unit in a similar manner is imaged on a two dimensional matrix array of charged coupled devices (CCD) (32). The test pattern is projected in sequence by each of the three CRT projectors (50,54,58,14,16,18) of the system, and during the projection of the test pattern, the position of the centroid (40) of each unit of the test pattern is determined from the light intensity pattern received by the CCD matrix array, and stored (112). The centroid positions of each unit of a test pattern of two of the projectors are compared with positions of the centroids of each unit of the test pattern projected by a third one of projectors.