Hi ~ Thank you for helping me I use the Q03UDVCPU this time. I set a TPC MC Protocol 3000 port on the Built-in Ethernet to give PC to connection. The ethernet cable configuration is the PLC CPU link to Switch and link to PC. The problem is that when the PC is connected to the PLC, I use the Ethernet diagnostic of Work 2, you can see that the port 3000 is occupying by PC. There is no problem here, but when I remove the ethernet cable the PC, this 3000 port should be cleared, but the IP still occupying this 3000 port, until I remove the PLC CPU ethernet cable, it is the same result, and my PC can no longer be reconnect. Since the ethernet cable are all removed, the connection status should be updated, I don't understand why it is still occupying. Does anyone know the answer? Thank you so much!