| 摘要 |
PURPOSE:To attain incoming data transmission by a terminal device subjected to polling by transmitting a transmission carrier at non-communication to each transmission line between a central controller and each terminal device and detecting the interruption of carrier at polling. CONSTITUTION:Two-way data communication by using polling is executed among one central controller 100 and plural terminal devices 180, 190, 191...192. The center controller 100 consists of a central processing unit 101 applying centralized control of communication, a modulator 112 applying frequency modulation of data to each terminal device and transmitting it, a demodulator 113 demodulating the data frequency from each terminal device, a carrier transmission line 111 to inform the occupying state of transmission lines 171, 172, 173, 174 and the demodulator 113 to each terminal device, band pass filters 121-123 regulating the frequency band width of an input/output signal, an analog signal changeover switch 150 and coupling circuits 161-164. |
