| 摘要 |
PURPOSE:To simplify the supervisory to the breakdown of terminal controllers and to shorten switching time when it breaks down by providing a supervisory circuit supervising the operation of the terminal controllers through the use of a watch dog timer and a switching device. CONSTITUTION:When the supervisory circuit with watch dog timer 11 in the switching device 10 writes write data 25 of 01, for example, for the terminal controller 20 through a supervisory line 21, the controller 20 receives data 25 and returns read data 26 to the circuit 11 within a fine prescribed time. Then, the circuit 11 checks data 26 at a constant period and judges it to be a normal operation when data 26 is returned. It judges it to be abnormal when data 26 is not returned owing to some cause. The terminal controller 30 is similarly supervised. When an abnormality is detected in one of the terminal controllers, supervisory data turns into a switching instruction as it is and it is transmitted to a switching circuit 12. Then, switching is immediately executed. Thus, the supervisory method of breakdown is simplified and the terminal controller speedily is switched when one controller breaks down. |
