DeviceNet to PROFIBUS Gateway for Servo Integration
In modern packaging lines, the biggest challenge isn’t always speed—it’s getting equipment from different eras and regions to communicate. A recent retrofit on a tea packaging line highlighted this perfectly. The line used a Siemens PLC running the robust PROFIBUS-DP protocol, while the precision filling station relied on an Inovance SV660 servo drive speaking DeviceNet. These two protocols, though both widely used in industrial automation, are fundamentally incompatible at the physical and data link layers.
Key Insight:
PROFIBUS-DP excels in high-speed cyclic data exchange, ideal for drive control and I/O. DeviceNet, based on CAN, offers flexible peer-to-peer communication and power on the bus. Bridging them requires more than a simple adapter—it demands a protocol gateway with real-time translation capabilities.
The Protocol Divide: PROFIBUS-DP vs. DeviceNet
PROFIBUS-DP (Decentralized Periphery) is a fieldbus standard defined in IEC 61158. It uses a master-slave architecture, typically with a PLC as the master polling slaves cyclically. Data is transmitted in DP-V0 or DP-V1 frames, supporting up to 244 bytes of I/O per slave. The physical layer is RS-485, with baud rates up to 12 Mbps. In contrast, DeviceNet is built on the CAN (Controller Area Network) protocol, using a multi-master, producer-consumer model. It supports up to 64 nodes, with data packets limited to 8 bytes per message. DeviceNet cables carry both signal and power, simplifying wiring for sensors and actuators.
The incompatibility is stark: different connectors (9-pin D-sub vs. 5-pin open-style), different voltage levels, and different data structures. A PROFIBUS master cannot directly interpret a DeviceNet I/O message, and vice versa. This is where a dedicated gateway becomes essential.
The Real-World Problem: Costly Alternatives
In the tea packaging line, the options were grim. Replacing the Siemens PLC with a DeviceNet-compatible controller would cost tens of thousands of dollars and require rewriting the entire process program—causing at least two weeks of downtime during peak season. Running the servo in open-loop mode without feedback wasted its precision. The solution had to preserve the existing control system while enabling full servo functionality.
How the DeviceNet to PROFIBUS Gateway Works
A protocol gateway acts as a translator. On the PROFIBUS side, it appears as a standard slave device. On the DeviceNet side, it can function as a master or slave, depending on configuration. In this case, the gateway was set as a DeviceNet master to control the servo. The integration process involves three steps:
- Hardware Configuration: In Siemens STEP7, the gateway is added as a PROFIBUS-DP slave using its GSD file. This file defines the module’s I/O data sizes—typically configurable from 16 to 128 bytes of input and output. The gateway occupies a unique station address (1-125) on the PROFIBUS network.
- Data Mapping: Inside the gateway’s configuration tool, you map PROFIBUS I/O bytes to DeviceNet I/O assemblies. For example, the first two output bytes from the PLC might map to the servo’s Control Word (0x6040) and Target Velocity (0x6042). Input bytes from the servo—Status Word (0x6041), Actual Position (0x6064)—are mapped back to the PLC’s input area.
- Seamless Operation: Once mapped, the PLC treats the servo as a local PROFIBUS node. The gateway handles all protocol conversion, including CAN message fragmentation for data larger than 8 bytes, and manages the DeviceNet connection (Explicit or I/O messaging).
Technical Deep Dive: Data Mapping and Configuration
A typical gateway supports multiple I/O connection types. For servo control, a Polled I/O connection is common, where the master (gateway) cyclically sends command data and receives status data. The mapping table might look like this:
| PROFIBUS Byte Offset | Direction | DeviceNet Object (CIP) | Function |
|---|---|---|---|
| 0-1 | PLC → Gateway | Control Word (0x6040) | Enable, fault reset, operation mode |
| 2-3 | PLC → Gateway | Target Velocity (0x6042) | Speed setpoint (RPM or user units) |
| 4-7 | Gateway → PLC | Status Word (0x6041) | Ready, enabled, fault, warning |
| 8-11 | Gateway → PLC | Actual Position (0x6064) | Encoder feedback (counts or units) |
The gateway’s GSD file defines these modules. In STEP7, you select the appropriate module (e.g., “4 Byte Out / 8 Byte In”) during hardware configuration. The gateway then handles the cyclic data exchange at the configured PROFIBUS baud rate (typically 1.5 Mbps or higher). On the DeviceNet side, the gateway must be set to match the servo’s MAC ID and baud rate (125, 250, or 500 kbps).
Benefits Beyond Simple Connectivity
The gateway approach delivers several operational advantages:
- Asset Preservation: No need to replace the PLC or servo. The gateway costs a fraction of a new controller and can be installed in hours, not weeks.
- Full Servo Performance: Real-time position, velocity, and torque control are maintained. The servo’s advanced features (electronic gearing, camming) can be utilized via parameter access over DeviceNet.
- Scalability: One gateway can often handle multiple DeviceNet nodes (up to 63 slaves), allowing additional servos or I/O blocks to be integrated later.
- Diagnostics: Many gateways provide web-based status pages or diagnostic LEDs, showing network health, data traffic, and error counters for both buses.
Practical Tip: When configuring the gateway, always verify the endianness (byte order) of multi-byte data. PROFIBUS typically uses big-endian, while DeviceNet (CAN) uses little-endian. The gateway must swap bytes if necessary to ensure correct interpretation of values like position and speed.
Real-World Application: Tea Packaging Line
In the tea packaging line, the gateway enabled the Siemens PLC to command the Inovance servo’s speed and position with sub-millisecond update rates. The filling accuracy improved because the PLC could now adjust the servo’s motion profile based on feedback from upstream drying sensors. The integration took less than a day, and the line was back in production with zero process changes. This retrofit exemplifies how protocol gateways bridge the gap between legacy systems and modern components, extending the life of capital equipment while embracing new technology.
Choosing the Right Gateway
When selecting a DeviceNet to PROFIBUS gateway, consider these factors:
- Data Capacity: Ensure the gateway supports enough I/O bytes for your application. Servo control typically needs 10-20 bytes of cyclic data per axis.
- Configuration Software: Look for user-friendly tools that simplify mapping and provide diagnostic views.
- Certifications: Industrial environments demand CE, UL, or ATEX certifications. Check for PROFIBUS and DeviceNet conformance testing.
- Environmental Ratings: For packaging lines, IP20 may suffice, but food and beverage often require IP65 or higher.
In conclusion, a DeviceNet to PROFIBUS gateway is not just a wiring convenience—it’s a strategic tool for industrial automation upgrades. It allows plants to mix best-in-class components without being locked into a single vendor’s ecosystem. As factories move toward Industry 4.0, such interoperability becomes critical, and the humble gateway proves that sometimes, the most valuable innovation is the one that connects what already exists.
