| 摘要 |
PURPOSE:To improve the calling state, by connecting a detecting circuit in parallel with a subscriber line to detect the on and off signals of a handset and switching forcibly the state of the data transmission. CONSTITUTION:The voltage between optional points A and B of a telephone subscriber 4 is kept at -48V and -5V when the handset is hooked on and off respectively. When the handset is hooked on from the off-hook state, the voltage of the point B is set at an earth level with the voltage of the point A changed to -48V from -5V. This change is differentiated by differentiating circuits C1 and R1, and a transistor TR1 is switched by the output of differentiation. Then a pulse output is generated from an NAND gate G1 by the switching output of the TR1. Then an FF9 is reset, and a modulating/demodulating circuit 3c is set in the receiving mode by the output of the circuit 3c. Furthermore the detecting signal is applied to a circuit which is not shown in the diagram. Thus the received data is set in the non-data state. |
