| 摘要 |
PURPOSE:To eliminate the consecutive use of resource relating to the retention continuity in an exchange by detecting it by a detection circuit when a signal representing the disconnection of opposite party is sent from an exchange after retention so as to release the holding state. CONSTITUTION:If the holding of a telephone set is desired due to any reason during talking, a holding switch 55 is closed. Through the closing, a transistor (TR) 50 is turned on and a DC output Vcc of a talking circuit 16 is fed to a base of a TR 40 via a holding tone generating circuit 52 and a diode 54. If the other party hooks on after the holding, a busy tone signal is sent from the exchange to a telephone set during holding. A switching element is closed by the detection output. Thus, the output voltage of the TR 50 goes to a low level, the TRs 40, 18 are turned off and the loop formed by holding is released.
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