Abstract: In a color graphics display system, video analog self-test hardware for testing the system elements between the frame buffer and the CRT display monitor is provided including a bi-directional data bus between the graphics processor and the color map, an analog comparator, an integrator, and an analog multiplexor. The self-test method includes calibrating the self-test circuitry with respect to a reference voltage. The method next includes testing the DACs by outputting predetermined bit patterns to each of the DACs via the frame buffer, measuring each DAC output level in response to each input bit pattern, comparing the DAC output levels to predetermined limits, and reporting the results. Provision is made also for testing the system clock.

Abstract: A method and apparatus for generating two phase locked digital clocks of different word rates particularly suited for a graphic and alphanumeric computer display terminal. Master and slave clock generators are used to generate output pulses at every N-th and M-th clocks of a common clock. A phase lock loop including the master clock generator and a phase lock counter dividing the common clock by the factor of the least common multiple of N and M is used to synchronize the slave clock generator.