Siemens PLC to Lenze Drive via Modbus to EtherNet/IP Gateway
Industrial automation often demands integration of devices from different vendors, each speaking its own protocol. This article explores a practical solution for connecting a Siemens PLC using Modbus TCP to a Lenze drive that only supports EtherNet/IP, without costly hardware replacements.
The Challenge: Protocol Mismatch in a Machine Tool Retrofit
In a precision machining facility, an existing production line relied on a Siemens S7-1200 PLC (model 6ES7212-1AE40-0XB0) as the central controller. This PLC communicated with HMIs and sensors over Modbus TCP. When the plant upgraded to a Lenze i950 series drive (model EVS9326-ES) for better motion control, a problem surfaced: the Lenze drive only supported EtherNet/IP, while the Siemens PLC was set up for Modbus TCP. Direct communication was impossible.
Replacing the drive or upgrading the PLC would have been expensive and caused significant downtime. The engineering team instead turned to a protocol conversion gateway—a compact device that translates between EtherNet/IP and Modbus TCP in real time. This approach saved roughly 60% of the retrofit budget and avoided weeks of production loss.
How the Protocol Gateway Works
A protocol gateway acts as a bridge between two networks. On one side, it appears as an EtherNet/IP adapter (slave) to the Lenze drive. On the other, it functions as a Modbus TCP server (slave) for the Siemens PLC. The gateway maps data between the two protocols, allowing the PLC to read drive parameters like speed and current, and to send control commands.
Key specifications of a typical industrial gateway include:
- ▶ Dual RJ45 ports for simultaneous connection to both networks
- ▶ Support for up to 500 bytes of input and output data
- ▶ Operating temperature range of -25°C to 55°C for harsh environments
- ▶ Configuration via dedicated software with EDS file import
Step-by-Step Integration Guide
1. Network Planning and IP Addressing
All devices must reside on the same subnet. A typical setup uses an industrial Ethernet switch with shielded Cat5e cables for reliability. Assign static IP addresses:
| Device | IP Address | Role |
|---|---|---|
| Siemens S7-1200 PLC | 192.168.1.10 | Modbus TCP Master |
| Protocol Gateway | 192.168.1.100 | Converter |
| Lenze i950 Drive | 192.168.1.20 | EtherNet/IP Adapter |
2. Gateway Configuration
Using the gateway’s configuration tool, set the protocol conversion mode to “EtherNet/IP to Modbus TCP” bidirectional. Import the Lenze drive’s EDS file (e.g., Lenze_i950_EVS9326-ES.eds) to automatically populate the I/O assembly instances. Typically, Instance 100 is used for outputs (PLC to drive) and Instance 150 for inputs (drive to PLC). Define the data sizes—for example, 32 bytes for input and 16 bytes for output.
On the Modbus TCP side, create a device instance pointing to the PLC’s IP address and port 502. Map Modbus function codes: FC03 (Read Holding Registers) to read drive status, and FC06 (Write Single Register) to send commands.
3. Siemens PLC Programming
In TIA Portal, configure the Modbus TCP client. Create a data block (DB1) with tags for drive status word, actual speed (MD20), and setpoint speed (MD24). Use the MB_CLIENT function block to trigger read/write requests cyclically. The gateway handles the rest, converting Modbus requests into EtherNet/IP messages that the drive understands.
4. Lenze Drive Setup
Using Lenze’s FAST software or the drive’s keypad, enable EtherNet/IP communication. Set the adapter instance ID to 100 and the heartbeat interval to 500 ms. Map the actual speed (register 40001) to the input assembly and the control word (register 40010) to the output assembly. This ensures the gateway can access the right data.
Real-World Results and Benefits
After commissioning, the PLC could seamlessly monitor and control the Lenze drive. The retrofit delivered measurable improvements:
| Cost Savings | Avoided replacing the drive or PLC, saving approximately 60% of the budget. |
| Precision Improvement | Real-time data exchange improved machining accuracy by 0.02 mm. |
| Quality Rate | Product pass rate increased to 99.3%. |
| Downtime Reduction | Minimal production interruption during integration. |
Why Protocol Gateways Are Essential for Modernization
Many factories have legacy PLCs that speak Modbus TCP or Profinet, while newer drives and I/O blocks often come with EtherNet/IP. A protocol gateway eliminates the need to rip and replace equipment. It’s a scalable solution that can connect multiple devices, and it’s far less expensive than upgrading entire control systems.
When selecting a gateway, look for industrial certifications (CE, FCC), a wide temperature range, and support for common data sizes. Some advanced gateways also support OPC UA and TSN for future-proofing.
Pro Tip: Always test the gateway in a lab environment before deploying on the factory floor. Verify data mapping with a Modbus scanner and an EtherNet/IP scanner tool to ensure registers align correctly.
Looking Ahead: The Future of Industrial Protocol Conversion
As Industry 4.0 advances, gateways are evolving to support time-sensitive networking (TSN) and OPC UA, enabling deterministic communication and cloud connectivity. This allows machine tools and robots to share data with sub-millisecond precision, opening doors to predictive maintenance and AI-driven optimization.
For now, a Modbus-to-EtherNet/IP gateway remains a practical, cost-effective tool for integrating diverse automation components. It’s a proven method to extend the life of existing equipment while adopting modern drives and sensors.
