DeviceNet no communication — MAC ID, baud, power

DeviceNet (CAN-based, per ODVA — common with Rockwell) connects sensors, VFDs, MCCs, remote I/O. When the NET LED is red, a node drops, or the scanner faults, the cause is usually MAC ID, baud, terminator, or 24V bus power — not a faulty device.

Common causes

1. Duplicate/wrong MAC ID — two nodes on the same address → conflict, drop off the network.
2. Baud mismatch — a node at a different speed drags the whole network down.
3. Terminator — missing/wrong 121Ω at the two trunk ends.
4. 24V bus power — voltage drop at the far end, broken supply, insufficient current.
5. EDS / scanner config — missing EDS, wrong scanlist, mismatched I/O size.

Step-by-step diagnosis

1. Read MOD/NET LEDs NET flashing red = connection error; NET solid red = critical fault/duplicate MAC. Localize from there.
2. Check MAC ID & baud Each node a unique MAC, same baud network-wide; fix duplicates first.
3. Check terminators Correct 121Ω at both trunk ends; measure CAN_H–CAN_L (≈60Ω with both).
4. Measure bus power Check 24V at the farthest node; confirm sufficient voltage & current, solid connectors.
5. Scanner config Load the right EDS, check scanlist + I/O size match the device.
6. Isolate nodes Remove suspect nodes to confirm, then add them back one by one.

When to call an expert

DeviceNet bus-power/terminator/duplicate-MAC faults are hard to catch without tools. DeepDebug has CAN + Rockwell experience, supports remotely and localizes the offending node fast.