| 摘要 |
PURPOSE:To improve maintainability and expandability by allowing a central processing unit to detect an input/output device in operation, combining signals representing the operating state of each equipment serially among the equipments, and providing the priority of the operation based on the sequence of combination. CONSTITUTION:A CPU 1 controls a control object 6 via input/output devices 3-5. One of the devices 3-5 is operated and the others are brought into a standby state. Since no signal s0 comes from an adjacent device, the device 3 starts its operation and the devices 4, 5 are in the standby state by signals s1, s2. If the device 3 is faulty, the device 4 starts its operation by the signal s1. If the device 4 is also faulty, the device 5 starts its operation by the signal s2. Thus, the normal operation is obtained automatically in the event of the occurrence of fault. Moreover, the CPU 1 detects the fault through the absence of an acknowledge signal from the faulty device, and outputs alarm information to a display device 2 as soon as the CPU 1 changes over the access to the device of the next order.
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