| 摘要 |
PURPOSE:To detect response of a called party independently of the polarity of a line before the response of the called party by detecting the inversion of polarity of a telephone line as a pulse change of a photo isolator at the start of transmission/reception, and connecting a data transmitter/receiver to the telephone line to control the detected result. CONSTITUTION:When a transmission/reception start pulse is fed to a terminal A with a terminal L1 brought to negative level and a terminal L2 brought to positive level at the normal state of a telephone line, an FF is set, a transistor (Tr)1 is conducted, a P relay is operated, an S relay is self-held and an automatic dial device 2 is connected to the line. When the called party responds, the polarity of the terminals L1, L2 is inverted, a current at the diode of a photo isolator PF is disconnected and the potential at a point (a) of the input side of a gate ic1 is raised. A monostable multivibrator MM2 is triggered and generates a pulse, a Tr2 is conducted, a CML relay holds the operation and the data transmitter/receiver 1 is connected to the telephone line via contacts cml1 and cml2. |
