| 摘要 |
PURPOSE:To prevent the malfunction, by transmitting a connection fault diagnostic signal to respective key telephone sets periodically through a data line from a main device and by performing normal data receiving only when the connection completion signal from key telephone sets is normal. CONSTITUTION:A main device 10 and plural key telephone sets 20 are connected by two or more pairs of data lines for transmission and receiving and voice service lines, and a connection failt diagnostic signal is transmitted from a connection fault diagnostic circuit 15 of the main device periodically to respective key telephone sets. The connection completion signal transmitted from a receiving data processing circuit 24 in the key telephone set side is received by a receiving processing device 18 through a transmitting circuit 26; and if the connection completion receiving signal from the device 18 corresponds to the transmitted diagnostic signal, a normal connection is discriminated by the diagnostic circuit 15 to instruct the processing device 18 to perform the normal data processing. Thus, when line connections and telephone sets are abnormal, the operation of the processing device 18 is stopped by the diagnostic circuit 15 to stop the acceptance of data, thereby preventing the malfunction. |
