I am building a system with ethernet on a STM32F417. When I connect the circuit to my PC directly, the connection is established successfully when my ethernet cable has no ground connected to the shield. When I connect it with a cable where the shield is connected, the connection can not be established, both Ethernet LEDs are constantly on.
When I connect it to a switch, there is a similar problem. Independent of the cable, the LEDs are constantly on and no connection to the network is possible.
Has anybody an idea?