DIAGNOSTIC SYSTEM OF LOGICAL UNIT

PURPOSE:To simplify a diagnostic procedure and shorten the time required for diagnosis by writing diagnostic data in shift buses as they are. CONSTITUTION:When diagnosis is performed, stored data are read out from an external memory 13 and these data are written in shift buses 30 and 40 as they are. Then, a clock is set forward, the contents of the shift bus 30 are read out, and the values of memory elements 33 and 35 are verified. In diagnosis of a diagnosed device 20, writing twice in each of shift buses 30 and 40 is enough by setting of diagnostic data for combination of diagnosed circuits 24, 26 and 28 and combination of diagnosed circuits 25 and 27. In reading of the contents of shift buses, it is enough to read out the result of diagnosis of combination of diagnosed circuits 24, 26 and 28 and combination of diagnosed circuits 25 and 27 twice for the shift bus 30, and read out the result of diagnosis of combination of diagnosed circuits 24, 26 and 28 once for the shift bus 40.