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We have a system use S7-313 CPU (MPI) communication with CP5412A2 and a RS485 repeater between CPU and CP card. S7-313 CPU CP5412A2 RS485 repater Simatic Net S7-Profibus The problem is all LEDs of 313 CPU will flashing after a period of irregular time and we found the following event into the STEP 7 ver. 5.0 "Diagnosis Buffer". Event: DEFECTIVE: internal system error EVent ID: 16#4550 Detail on Event: DEFECTIVE : internal system error No relevance for user (Z1) : 7190 Previous operating mode : RUN Requested operation mode : DEFECTIVE Internal error, Incoming event