In a flash unit used with camera for providing stop value data consisting of a frequency clock, a circuit which can detect stop value data consisting of a frequency clock or the like provided from the flash unit without being influenced by noise by permitting the stop value data to be accepted when the data is confirmed to be a continuous normal signal. Where the camera is provided with a TTL flash automatic light does control unit, the circuit permits the use of a common circuit for a path through which the detecting circuit receives the stop value data and for a path through which the TTL flash automatic light dose control unit provides automatic light dose control data to be flash unit, thus permitting simplification of these data transmitting system.
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