REDUNDANT DISTRIBUTED CONTROLLER

PROBLEM TO BE SOLVED: To surely perform self-diagnosis of a communication system by performing test communication for reading a test pattern previously stored in a memory inside a 1st controller as the self-diagnosis of the communication system. SOLUTION: First of all, the fixed test pattern is stored in the memory inside a controller 4a of a slave station. As a master station, a controller 7a reads the test pattern for the controller 4a of the slave station as the test communication while using communication cards 2a and 3a. When the controller 7a of the master station successfully reads out the test pattern, it can be judged there is no abnormality on these communication cards 5a and 6a. When there is any fault at the part of interface on the communication card 5a with the controller 4a, on the other hand, the test pattern stored in the memory can not be accessed and it becomes an error. Namely, when the communication with the communication card 5a becomes the error, the controller 7a of the master station can detect the fault on the communication card 5a.