JPS6484938A - Data communications control system - Google Patents

Abstract

PURPOSE:To suppress and influence exerted on communications between other subcontrol devices and a main control device by operating a change-over switch in the control device at the time of interrupting/inputting the power source of the subcontrol device. CONSTITUTION:At a normal time, change-over switches 22 and 32 of subcontrol devices 2 and 3 are in on states, respectively, and since the disable terminals of respective transmitting and receiving elements 20 and 30 are earth potentials, a main control device 1 can be communicate with both the devices 2 and 3. At present, due to the trouble generation of the device 2, the power interruption is required. Here, when only the devices 1 and 3 execute the communications and the device is not communicated with, first, when the switch 22 is turned off before a power source part 21 is interrupted, since an H level is given through a resistor 12 of the device 1 to the disable terminal of the element 20, the element 20 goes to a disable condition. Since, for the element 20, the disable condition is held even when the power source of the power source part 21 is interrupted in such a condition, the element 20 cannot influence a bus 4. It is all the same also as the time of inputting the power source.