| 摘要 |
PROBLEM TO BE SOLVED: To normally operate an instrument without causing the abnormal operation of an additional circuit even when an additional circuit connecting terminal is short-circuited with a terminal adjacent thereto by dust by connecting a receiving terminal to an input port, and substantially laying the receiving terminal into released state in the state where no external device is connected to a communication connector. SOLUTION: In general use, a communication connector 3 is laid in non-used state without connecting an external device thereto. Since the input port 6 of a microcomputer 1 connected to a receiving terminal 13 has a high input impedance, the receiving terminal 13 is substantially laid in released state. Thus, even if the receiving terminal 13 is short-circuited with an additional circuit connecting terminal 15 by dust, any signal from the communication connector 3 side is never imparted to the input port 9 of a watch dog circuit 2 connected to the additional circuit connecting terminal 15. Therefore, the watch dog circuit 2 is normally operated according to only the output from the watch dog output port 7 of the microcomputer 1. |
