DeviceNet — CIP over CAN

DeviceNet is an ODVA fieldbus that carries the Common Industrial Protocol (CIP) — the same object model used by EtherNet/IP — over CAN (ISO 11898). It is common in older Rockwell and Omron installations for drives, starters, valve islands and sensors. New designs normally use EtherNet/IP, but many lines still run DeviceNet.

Physical layer

• 4-wire cable plus shield: CAN_H, CAN_L and 24 V DC network power (V+, V−).
• 121 Ω terminating resistors at both ends of the trunk (not on drops). Single drop length max 6 m.
• Up to 64 nodes, MAC ID 0–63 (63 is often the default of new devices — change it before connecting).

Communication model

• Explicit messaging — request/response access to CIP objects (parameters, identity).
• I/O messaging with connection types: Polled, Strobed, Change of State (COS) and Cyclic.
• The scanner (master) holds a scan list; devices are described by EDS files.

Typical faults

1. Duplicate MAC ID or wrong baud rate → node does not come online.
2. Missing/extra termination → bus errors and bus-off; measure about 60 Ω between CAN_H and CAN_L with power off.
3. Network power voltage drop on long trunks or too many devices on one supply.
4. Shield grounded at several points or not at all.
5. Scan list mismatch after device replacement (I/O size, product code, electronic keying).