with devicenet protocol only following things need to be check:-
1. IO mapping input output byte size.
2. 24V and 0V supply to devicenet module at either robot side or powersource side
3. A 120 ohm resistor to end the brach at either robot side or powersource side, between CAN high and CAN low.
4.proper connections at both side.
5. Changing faulty module.
6.Continuty check