DATA PROCESSING SYSTEM

PURPOSE:To prevent heat from being generated by detecting a fault by adding simple hardware by providing a means to detect the fault of a register in a data processor by data of scan-out, and switching the bidirectional buffer of the data processor to an input side by the output of the means. CONSTITUTION:A scan path fault detection register 13 is connected between an enable register 12 and a scan path (b), and detects the fact that a fixed fault occurs in registers 111, 112. In such a case, it is assumed that the fixed fault occurs in the first register 111 when the scan-out of the scan paths (b) of the data processors 1-3 are performed. Thereby, logic 1 is set at the scan path fault detection register 13. Since the signal of logic 1 represents the fact that one fixed fault occurs in the scan path (b), the enable register 12 is set at logic 0 replying to the signal of logic 1. Therefore, the bidirectional buffer 10 is switched to the input side.