| 摘要 |
PURPOSE:To improve the efficiency of processing relating to polling by applying polling to a corresponding terminal device only when a state change takes place at the terminal device side in a terminal centralized controller. CONSTITUTION:When a state change takes place in a terminal device 15, a signal A starts a polling request signal sending circuit 16 to invert the logical level of a coaxial cable 14 for a prescribed time. When a polling request signal detection circuit 10 of the terminal centralized controller 8 detects that the logical level of the coaxial cable 14 is inverted, a bit corresponding to each terminal device of a register 11 is set to ON-state. Then an interruption generating circuit 13 is started via an OR circuit 12. A control processor (not shown) uses the interruption signal to send a polling command to the corresponding terminal device 15 through the coaxial cable 14. Then the state change of the terminal device 15 is recognized by using a reply signal.
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