Vertical reset generation system

摘要

A video display control system comprises a display for the video signal, a vertical zoom circuit for generating from the video signal a picture having a vertical height greater than the display, and, a vertical panning circuit for displaying a selected portion of the picture on the display by generating a time delay relative to a vertical synchronizing component of the video signal. A counter and comparator measure the respective durations of successive fields of the video signal and the time delay. A circuit responsive to the comparing means generates a first signal for initiating delayed reset pulses when a field of the video signal and the time delay match in duration. Another circuit generates a second signal for initiating the delayed reset pulses in accordance with the vertical synchronizing component. A gating circuit selects the first initiating signal as an output, if present, and selects the second initiating signal as an output absent detection of the first initiating signal. A further counter generates the delayed vertical reset pulses responsive to the output selected by the gating circuit.