| 摘要 |
PURPOSE:To detect a horizontal scanning period H immediately by providing a counting means which counts character signal packets at every horizontal scanning period H and a detecting means, and comparing the number of character signal packets of respective periods H and detecting the H corresponding to the largest number of packets. CONSTITUTION:Counters 61, 62...6n for the number of character signal packets corresponding to H (where a character signal is superposed possibly) in the vertical blanking period of a video signal count character packets in respective Hs. On the other hand, data superposed in each H are detected and when data is a character broadcast packet, it is counted as a packet of the corresponding H and the counter value of a packet number counter is increased. An H detecting circuit 7 compares counted values of the number of character signal packets of the respective Hs to detect the H corresponding to the largest number and decide it to be a transmission H (where the largest number of character signals are superposed), thereby outputting the H number. Consequently, malfunction due to momentary variation of a received signal is absorbed.
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