Standard/nonstandard internal vertical sync producing apparatus

Claim 1

Apparatus for producing internal vertical sync signals at an output terminal in response to standard and nonstandard rate external vertical signals, comprising: first resettable counting means responsive to said external vertical signals, the count of said first counting means being incremented in response to a source of incrementing signals repeating at a frequency integrally related to the frequency of said standard rate external vertical signals, said first resettable counting means being reset in the presence of said external vertical signals; coincidence means coupled to said first counting means and responsive to said external vertical signals for providing a coincidence signal when said external vertical signals are repeating at a standard rate; detection means responsive to said external vertical signals for providing after the elapse of a predetermined time interval a detection signal indicative of the presence of said nonstandard rate external vertical signals; second resettable counting means responsive to said source of incrementing signals for providing only a standard rate internal signal; first signaling means coupled to said second resettable counting means and responsive to said detection signal and said external vertical signals for providing in place of said standard rate internal signal a nonstandard internal signal repeating at a nonstandard rate; and sync producing means responsive to said coincidence signal, said standard rate internal signal and said nonstandard internal signal for producing said internal vertical sync signals upon the occurrence of one of said coincidence signal, said standard rate internal signal and said nonstandard internal signal, said second counting means being reset upon such occurrence.