| 摘要 |
PROBLEM TO BE SOLVED: To control a communication channel to which an information terminal is connected. SOLUTION: In the standby state of a TEL-FAX changeover circuit 6, the circuit 6 is thrown to the position of (a) and a polarity detection circuit 1 connects with a terminal (a), and then line terminals L1, L2 connect with telephone set terminals T1, T2 and a communication controller 4 or the like in a communication line with which an information terminal connects. In the FAX reception mode, a call signal detection circuit 5 detects a call signal, a line closing circuit 2 closes a line to be set to the reception mode. In the automatic changeover mode of an automatic answering telephone set, the automatic answering telephone set closes the line, and when a phone call is received, automatic answering recording is conducted. Upon receipt of a CNG signal, a tone signal detection circuit 5 closes the line to be set to the reception mode, the TEL-FAX changeover circuit 6 is thrown to the position of (b) and a telephone set connects with a DC voltage application circuit 7. In this case, the recording is stopped if the polarity is different from that of the line, and an operation section sets the polarity by a polarity changeover circuit 9 to prevent malfunction of the telephone set. |
