Apparatus for detecting nonstandard video signals

摘要

Circuitry for detecting nonstandard video signals is disclosed. This circuitry is used in a sampled data video signal processing system to control signal processing steps which utilize a frame store memory. The detecting circuitry includes a programmable counter which generates a standard horizontal pulse signal having a 70 ns pulse width by counting down a sampling clock signal that has a frequency proportional to the color subcarrier frequency of the video signals. The circuitry generates another horizontal pulse signal having a pulse width of less than 140 ns from the horizontal sync pulses of the input video signals. These pulse signals are compared in a coincidence detector which produces a signal that is in a first state when the pulses of the two signals overlap at least once in every twenty-five horizontal line times and in a second state otherwise. This coincidence signal and the field rate vertical synchronizing signal from the input video signal are used to generate the control signal for the frame store memory. This control signal is in a first state when the coincidence signal has been in its first state for at least one frame time and that changes to a second state when the coincidence signal changes to its second state.