The invention discloses a method and device of detecting circuit signal appearance in a detecting cycle, which detects circuit-receiving signal. If the signal is an idle level signal constantly, it will generate idle level indication signal with outputting the controlling signal; otherwise, it will not generate indication signal. When it receives controlling signal, it will not generate circuit signal disappearance indication signal. The circuit signal disappearance detection device comprises the following parts: level transformation circuit, circuit signal disappearance detection circuit, multi-idle level detection circuit, multi-latch circuit, idle detection circuit and filter circuit. |