| 摘要 |
PURPOSE:To improve the practicality by providing a PB signal generating circuit, a DP signal generating circuit and a signal control circuit. CONSTITUTION:The output signal of a switch group 2 is sent to a signal control circuit 3 by depressing a corresponding switch to a called party number of the key dial switch group 2, the signal is converted into a signal controlling a DP signal generating circuit 5, sent to an exchange via a subscriber line as a dial pulse signal, detected and connected with the called subscriber. When the called party replies, a reverse signal inverting the polarity is returned from the exchange side to the subscriber line, the reverse signal is detected by a polarity inversion detection circuit 6 and sent to the signal control circuit 3. On the other hand, the output signal of the witch group 2 is sent to the signal control circuit 3 by depressing the corresponding switch to the caller number of the switch group 2 according to the signal tone representing the caller number request sent from the called party, the signal is converted into a signal controlling the PB signal generating circuit. Thus, the practicality is improved.
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