EtherNet/IP: The Allen-Bradley Protocol
Allen-Bradley PLCs use EtherNet/IP (Industrial Protocol), not OPC-UA or Modbus. It is a robust, real-time protocol but requires specific libraries to communicate. The most reliable open-source option is the Python pycomm3 library or Node.js ethernet-ip package.
Reading Tags from ControlLogix
Unlike Modbus (register addresses) or OPC-UA (address space), Allen-Bradley systems use symbolic tag names — exactly as defined in RSLogix. You read ProductionCount not register 40001. This makes integration more intuitive once you understand the tag structure.
Setting Up the Python Gateway
Install pycomm3 and create a polling service that reads your required tags every second. Store values in Redis for sub-millisecond access by your API, and write to MySQL every 30 seconds for historical trending. This three-tier approach handles both real-time display and long-term analytics.
Security Considerations
Allen-Bradley PLCs on a factory network should never be directly exposed to the internet. Always place your gateway server in the DMZ between the factory network and the cloud. Use VPN or TLS tunnelling for cloud connectivity.
Allen-Bradley integration is straightforward with pycomm3 or ethernet-ip. The tag-based addressing is actually more readable than Modbus registers once your team gets familiar with it.
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