| 摘要 |
PURPOSE:To cope with frequent extension of individual input sections without decreasing the transmission efficiency of a communication line, by providing a means omitting the transmission of data to the individual input section not returning a signal representing actual devices. CONSTITUTION:An individual input section 1-X and a word scanner 2'' are connected with a control signal bus 6 other than an address bus 4. When an address ADX is outputted, and when the individual input section 1-X assigned with the address ADX is mounted, a decoder 11 discriminates the address ADX transmitted from the bus 4 and outputs ''1'' and makes a gate 12 conductive. On the other hand, when the input section 1-X is not mounted, even if the address ADX is outputted from the scanner 2'' to the bus 4, no control signal CS is outputted to the bus 6. As a result, a gate 24 of the scanner 2'' is conductive, a clock signal CL immediately advances a step counter 21 by one step via gates 24 and 23 and outputs the next address. |
