| 摘要 |
PURPOSE:To constitute easily a fail-safe device, by providing two pairs of CPUs and timers and setting supervising time values slightly different from each other to respective timers, and detecting counted values at expiration time of respective timers. CONSTITUTION:A dual device is constituted with pairs of CPUs 1 and 2 and timers 3 and 4. Timers 3 and 4 input their expiration outpus to their own side interrupt terminal INT0 and opposite side interrupt terminal INT1 by the control of CPUs 1 and 2. The CPU1 sets a monitor time Ts to the timer 3, and the CPU2 sets a supervisng time Tm slightly longer than the monitor time Ts to the timer 4. When the timer 3 expires, the CPU1 switches the supervising time Ts to said time Tm, and the counted value of the timer 4 is inputted to the CPU2, and the timer 3 is judged to be normal if this value is 0-(Tm-Ts). When the timer 4 expires, the supervising time Tm is switched to the said time Ts, and the CPU1 judges the timer 4 on a basis of the counted value of the timer 3. Thus, the malfunction due to common mode noise is prevented. |
