| 摘要 |
PURPOSE:To perform simultaneous broadcast to slave devices having encryption function made to the general reception state, by connecting a master device and a plurality of slave devices with a common transmission line, attaining callout and response among the slave devices, and applying a predetermined control voltage from the master device to the transmission line. CONSTITUTION:One set of a master device and a plurality of sets of slave devices are connected with three transmission lines 3-5 for common use. A power supply is given to the entire device from a DC power supply circuit 6 of the master device, a channel of a transmission and reception circuit 8 of a device is opened with a callout control circuit 13 for the master and slave devices to prevent the callout from the 3rd party. An opposing callout code is generated from a callout code generating circuit 18, the code is super-imposed on a call tone signal from a call tone generating circuit 22 to generate a signal waiting for lines. A communication signal, a callout signal, a callout preventing signal and a simultaneous broadcast signal are transmitted to a line 4, slave devices having encryption function are made to the general reception state with a predetermined control voltage from the master device to attain simultaneous broadcast. |
