I'm currently trying to get the Ethernet Shield + Mifare RC522 running. Each device on it's own is running like charm. But when I put them together they won't work any more. I connected the MISO/MOSI/SCK of both devices. The Shield of course uses Pin 10 for Chip Select. The RC522 is using pin 51. So there shouldn't be any mistake in wiring?
After some googling I found out that the Ethernet shield supposed to have an flaw in its circuit. It doesn't mater if you put HIGH or LOW to the Ethernet Shields chip select pin. It always reads/writes from/to MISO/MOSI. Can you confirm this issue? Has the current version of the Ethernet shield a fix for that? Or how can these be fixed?
Some posts in the internet said that using an signal inverter for chip select and connecting it to the SEN pin of the W5100 should fix this. I tried that but it didn't worked. Maybe I made a mistake. I'm not quite sure if I located PIN 31 correctly.
Sorry for my bad english. I hope somebody can help me :)