DeviceNet: Robust Protocol for Industrial Automation

DeviceNet is a widely used network protocol in the automation industry, designed to interconnect control devices for seamless data exchange. By utilizing the Common Industrial Protocol (CIP) over a Controller Area Network (CAN) media layer, DeviceNet offers an efficient solution for various applications, including information exchange, safety devices, and large input/output control networks.

History of DeviceNet

DeviceNet was initially developed by Allen-Bradley, a subsidiary of Rockwell Automation. It is based on CAN technology, originally created by Bosch, and it integrates aspects of the Common Industrial Protocol. DeviceNet’s design allows it to be low-cost and robust compared to traditional protocols like RS-485.

To promote its use globally, Rockwell Automation adopted an open approach, sharing the technology with third-party vendors. This led to the establishment of the Open DeviceNet Vendors Association (ODVA), which now manages DeviceNet and maintains its specifications. ODVA also conducts conformance testing to ensure compliance with DeviceNet standards.

DeviceNet is part of the broader Common Industrial Protocol, which also includes Ethernet/IP and ControlNet. The close relationship between these technologies simplifies industrial controls and has led to DeviceNet being standardized as IEC 62026-3.

Architecture of DeviceNet

DeviceNet’s architecture can be described using the OSI seven-layer model, primarily focusing on the physical layer, data link layer, and application layer.

1. Physical Layer

DeviceNet supports a trunk-line dropline topology, allowing nodes to be distributed easily across the network. This topology simplifies wiring and provides access to the network from multiple taps, facilitating easy removal and addition of nodes, thus minimizing production downtime.

DeviceNet supports three bit rates: 125 kbit/s, 250 kbit/s, and 500 kbit/s. The maximum cable length varies with the data rate and cable type:

• 125 kbit/s: Up to 380 meters with flat cable and 100 meters with round cable.
• 250 kbit/s: Up to 250 meters.
• 500 kbit/s: Up to 100 meters.

Additionally, DeviceNet can power devices over the same bus, reducing network complexity.

2. Data Link Layer

The data link layer in DeviceNet is based on the differential serial bus of CAN. This approach minimizes bandwidth requirements for transmitting messages, allowing for smaller processors in devices. The data frame format is designed for efficiency, and upon sending the first packet, a Start of Frame bit synchronizes receivers on the network.

The CAN identifier (ranging from 0 to 63) is crucial for determining message priority. Lower identifiers take precedence over higher ones, ensuring efficient communication. DeviceNet employs a robust error-checking mechanism that provides high immunity to noisy environments, thus enhancing reliability.

3. Network Layer

DeviceNet operates on a connection-based network. Connections must be established via either the Unconnected Message Manager (UCMM) or a Group 2 Unconnected Port. Two types of messages are used within DeviceNet:

• Explicit Messages: These are data packets that generally require a response, used for configurations or non-time-sensitive data collection.
• Implicit Messages: These are time-critical packets used for real-time data communication.

An explicit message connection must be established before an implicit message connection can occur, allowing data to be routed to the corresponding node based on the CAN identifier.

Key Features of DeviceNet

1. Master-Slave Communication

DeviceNet primarily operates on a master-slave communication architecture, although it also supports peer-to-peer communication. This flexibility allows for multiple networks to function under a single master, accommodating various applications.

2. Node Addressing and Duplication Detection

A single DeviceNet network can support up to 64 nodes, with each node assigned a unique address (MAC ID) ranging from 0 to 63. New devices typically default to address 63, and DeviceNet includes a duplicate node address detection function to prevent communication conflicts.

3. High Noise Immunity

DeviceNet’s design allows it to function effectively in high-noise environments, making it suitable for industrial applications where electromagnetic interference can be a concern.

4. Open Standards and Global Adoption

The open standards approach promoted by ODVA has led to widespread adoption of DeviceNet across the automation industry, ensuring interoperability among devices from various manufacturers.

Conclusion

DeviceNet is a vital network protocol that enhances communication and data exchange among control devices in the automation industry. Its robust architecture, flexibility in communication, and focus on reliability make it a preferred choice for many applications. As technology continues to evolve, DeviceNet remains a cornerstone of modern industrial automation, helping businesses streamline processes and improve efficiency.