| 摘要 |
a tuner for selecting a broadcasting signal of a constant frequency band of broadcasting signals received from a public network; an intermediate frequency amplifying part for generating an intermediate frequency signal by frequency converting the broadcasting signal selected by the tuner; a sound processing part for demodulating the intermediate frequency signal inputted from the intermediate frequency amplifying part, and sending the sound signal to a speaker; an image detecting part for inputting an image intermediate frequency signal outputted from the intermediate frequency amplifying part, and outputting a composite image signal; a color demodulating part for color demodulating the composite image signal into a chrominance signal for a general television video program; a monitor controller for compounding the analog letter information signal with horizontal and vertical synchronizations and a luminance signal, and outputting a color signal for the letter information; a switching part for selecting one of the chrominance signal and the color signal by means of a mode selecting signal, selecting the output color signal of the monitor controller during a predetermined time through an input of a mode conversion signal, and selecting the output chromainance signal of the color demodulating part to thereby output the selected signal to a CRT; a letter information reception detecting part for generating a letter information reception detecting signal to inform that the letter information is received when the letter information is detected from the composite image signals inputted from the image detecting part under an input of a first operation control signal; an automatic switch controlling part for generating the mode conversion signal and applying the signal to the switching part by means of the mode conversion selecting signal; and an automatic switch selection detecting part for sending the mode conversion selecting signal.
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