| 摘要 |
PURPOSE:To facilitate key operation by detecting a fault in the following key operation when a key input can not be detected owing to the malfunction of CPU, by sending a system reset signal or interruption signal from a delay output circuit to CPU after detecting the key operation. CONSTITUTION:Every time CPU reads key input data from keyboard interface circuit KI, CPU outputs key input detecting signal S1. Key operation is detected by key operation detecting circuit 20 and when CPU operates normally to output signal S1, the output of counter 4 of circuit 20 is applied to delay output circuit 30 to reset FF6 of circuit 30 with signal S1. If CPU is abnormal and incapable of outputting detecting signal S1, the output of gate 7 is inverted when monostable multivibrator 5 of circuit 30 recovers a constant time later. Then, an interruption signal or system reset signal S2 is sent to CPU, eliminating the need for the operation of a power switch and resetting switch. |
