| 摘要 |
PURPOSE:To eliminate the necessity of a circuit exclusively used for changeover control by transmitting a transmission request controlling signal to simplify a switching system, by disconnecting a carrier wave sent out from an MODEM, and forming change-over controlling information by utilizing the transmission request controlling signal. CONSTITUTION:When the data communication between the terminal device 5 at the terminal device side 1 of a modulator and demodulator system and the communication controlling device 8 at the central device side 2 is disconnected due to the fault of the presently used MODEM3 at the terminal device side 1, the device 8 performs the ON-OFF control of a transmission request controlling signal to the device 7 at a previously fixed time interval and repeating pattern and intermits the carrier sent out from the device 7. The intermission is detected by the carrier detecting circuit 10 of a device 6 for switching system and the detecting output is sent to a change-over controlling circuit 11. The circuit 11 decides whether or not the intermitting pattern coincides with a previously fixed pattern and, when it coincides, maintains the communication by switching contacts of switching relays 12 and 13 of the data circuit and digital data to a standby MODEM4 side. |
