Hello,
I am operating a PFC300 with three Profinet bus couplers 750-377. In the system, Profinet sporadically goes into fault for a short period every few days. The CPU then reports [Ethernet down] as the first error, but the program continues to run. Naturally, the entire system shuts down because all I/O were briefly lost. The power supply has always been stable, without interruptions or fluctuations.
We have already ruled out cabling as the cause. The cables were tested (they were error-free at 1000 Mbit). Initially, we wired them in a daisy-chain configuration (CPU–Coupler–Coupler–Coupler), replaced all cables, and now everything is connected in a star topology via a switch. The two interfaces of the CPU are configured separately, so Profinet has no connection to the other network. Increasing the bus cycle times in the Profinet task also did not bring any improvement. In the next system, we are now encountering the same problem.