A0 used by Ethernet shield
A1 used by Ethernet shield
A2: ...
A3: ...
A4: ...
A5: ...
D0: used by serial RX
D1: used by serial TX
Switch 1 (D2): ...
Switch 2 (D3): ...
D4: used by Ethernet shield
Switch 3 (D5): ...
D10 to D13 used by Ethernet shield