| 摘要 |
PURPOSE:To detect the simultaneous selection of plural slaves by connecting the collector of a transistor driven by a selected discriminating signal of the slave, through a resistance, to a common communication line connected to a power source by a resistance, and monitoring a voltage by a comparator. CONSTITUTION:A common signal line 10 to which an outputting circuit 1 of a selected discriminating signal of each slave is connected is connected to one input of a comparator 21, and simultaneously connected to a power source (E) by a pull-up resistance 22 (R0). When the selected slave is (n) = one piece an input voltage of a voltage monitoring circuit 21 becomes Vin=(E-Vsat)/(R0/r+ 1)+Vsat, and becomes a value below Vin=(E-Vsat)/(2R0/r+1)+Vsat, in case of (n)>=2. When a reference voltage Vrf of the comparator 21 is set to the middle of two values, it can be detected that plural slaves have been selected simultaneously.
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