| 摘要 |
<p>PURPOSE:To attain automatic backup in an intermittent fault of a specific communication line and a MODEM as well as a semi-permanent fault and also to give a switch command from a host device. CONSTITUTION:The line changeover controller of a data communication system backing up a specific communication line with an ISDN line is provided with an interface changeover section 17, a MODEM interface signal detection circuit 18, a normal/abnormal discrimination circuit 19, a control section 20 and an ISDN line interface section 21. The MODEM interface signal detection circuit 18 always monitors a CS signal of a MODEM interface signal and when the CS signal is set to a signal with monitor, after the CS signal is once set, the state of the OFF is detected. Furthermore, when the signal is not restored to ON for a set time or over, the normal/abnormal discrimination circuit 19 discriminates it to be a fault thereby selecting the specific communication line 3 and the ISDN line automatically.</p> |
