DIAGNOSING SYSTEM FOR COMMON BUS

PURPOSE:To find easily a faulty driver, by disconnecting the driver from a common bus if the driver connected to the common bus is in an on fault, and detecting the output level of the driver and the logical level of the bus. CONSTITUTION:The driver DV connected to the common bus is composed of an output transistor TRC and a disconnecting TRB as shown in a figure, and a terminal OUT is connected to the bus through the TRB. When a diagnosis indicating signal DIAG is held at 1 for diagnosis, an input signal IN to the driver DV and a driving input DVIN to the TRB both go down to 0, and the TRB turns off to disconnect the DV from the bus. At this time, a detection output CK is 1 when the TRs B and C are normal, but 0 when not. Therefore, fault display signals ER1-ER3 of the faulty driver DV are 1 and the fault is displayed.