| 摘要 |
PURPOSE:To prevent erroneous redialing, by detecting a backup power supply voltage, and inhibiting redialing operation when the detected voltage is less than a specific value. CONSTITUTION:When the charging voltage of a backup power source BUP is greater than a specific value, the output of a gate circuit G is at a low level and a transistor (TR) Q3 turns off. Therefore, when a dial key KRD is turned on after off-hook operation, a redialing signal RD is outputted from a TRQ2. On the other hand, when the voltage of the power source BUP is less than the specific value, the output of the gate circuit G is at a high level and the TRQ3 turns on. In this case, the TRQ2 is still off even when the key KRD is turned on, so no redialing signal RD is outputted. Further, the light emission of a light emitting diode LED is maintained to provide visible display for showing whether redialing is possible or not when the key KRD is turned on. |
