Allen-Bradley 1756-EN2TR/C EtherNet/IP Communication Module – ControlLogix

Allen-Bradley 1756-EN2TR/C — Dual-Port EtherNet/IP Redundant Media Module for ControlLogix Backplane Architecture

The 1756-EN2TR/C occupies a single slot in any 1756-series ControlLogix chassis and presents two independent 10/100BASE-TX ports to the plant network. Its primary function within a control loop is to serve as the deterministic EtherNet/IP bridge between the ControlLogix backplane bus and field-level devices — I/O adapters, drives, safety controllers, and HMI/SCADA nodes — while simultaneously maintaining ring-level media redundancy without requiring a managed switch infrastructure. Series C raises the maximum CIP connection count to 256 (double the 128-connection ceiling of Series A/B), which directly expands the addressable I/O and peer-controller population per chassis slot.

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Technical Parameters

Hardware Logical Analysis

The 1756-EN2TR/C integrates a dedicated ASIC-based DLR supervisor engine that operates independently of the host Logix controller’s scan cycle. When the module is configured as ring supervisor, it continuously transmits beacon frames at a user-configurable interval (default 400 µs) across both ring ports. Upon detecting a missed beacon threshold, the supervisor opens the ring at the fault point within the sub-3 ms window — a process executed entirely in hardware, not in ladder logic — ensuring that controller scan jitter does not influence network recovery timing.

The dual-port physical layer uses separate MAC controllers per port, each with its own receive and transmit FIFO buffer. This architecture prevents a broadcast storm or high-utilization condition on one ring segment from saturating the opposite port’s receive path, a failure mode common in single-MAC dual-port implementations. Port-level flow control (IEEE 802.3x PAUSE frames) is supported, allowing downstream managed switches to signal backpressure without dropping CIP I/O packets.

EMC hardening on the 1756-EN2TR/C follows the IEC 61000-4 series: 4 kV contact / 8 kV air ESD immunity (IEC 61000-4-2), 10 V/m radiated immunity at 80 MHz–1 GHz (IEC 61000-4-3), and 2 kV fast transient/burst immunity on signal lines (IEC 61000-4-4). The RJ-45 magnetics incorporate common-mode chokes rated to suppress differential noise up to 1500 V peak, which is particularly relevant in motor-drive-dense environments where VFD switching transients couple onto cable shields.

Backplane communication uses the ControlLogix proprietary high-speed serial bus operating at 200 Mbps aggregate throughput. The module’s local processor arbitrates backplane access using a time-division scheme synchronized to the chassis backplane clock, guaranteeing that EtherNet/IP I/O data is transferred to the controller’s I/O image table within a single backplane scan — typically under 1 ms for a fully loaded 256-connection configuration. This determinism is what distinguishes backplane-integrated communication modules from external gateway solutions, which introduce variable latency at the protocol translation layer.

System Integration Benefits

• Switchless DLR Ring Deployment: The module’s embedded ring supervisor eliminates the need for a managed Ethernet switch in ring segments of up to 50 nodes, reducing BOM cost and removing a non-deterministic switching element from the I/O path.
• Topology Flexibility Without Hardware Change: Linear, star, and DLR ring topologies are all supported from the same catalog number. Network architecture can be upgraded from linear to ring by adding a single cable run — no module replacement required.
• Integrated Motion on EtherNet/IP (IME): Series C supports Integrated Motion on EtherNet/IP at axis counts consistent with L7x/L8x controller capabilities, enabling servo drive coordination over the same network infrastructure used for standard I/O — eliminating a dedicated motion network layer.
• CIP Safety Routing: The module routes CIP Safety I/O connections between safety controllers (1756-L7xS) and safety I/O adapters, allowing a single EtherNet/IP network to carry both standard and safety traffic with full SIL 2 / PLd integrity maintained at the protocol level.
• Transparent Diagnostics via Studio 5000: Port-level statistics — packet counts, CRC errors, alignment errors, link speed, and duplex state — are exposed as controller tags accessible in ladder logic, enabling in-application network health monitoring without external SNMP infrastructure.
• Firmware Revision Management: ControlFLASH integration allows firmware updates to be scheduled and executed from the engineering workstation without physical access to the chassis, supporting remote maintenance workflows in geographically distributed plants.
• Redundant Controller Compatibility: Fully validated for use in ControlLogix redundancy systems (1756-RM2/K), where the module participates in the synchronization handshake between primary and secondary chassis, maintaining open CIP connections across controller switchover events.
• EtherNet/IP Conformance Certification: ODVA conformance-tested, ensuring interoperability with third-party EtherNet/IP devices from any ODVA member vendor without custom configuration or protocol bridging.

Quality Assurance & Global Logistics

Every 1756-EN2TR/C unit dispatched from our Xiamen, China facility is sourced through verified industrial supply channels and subjected to a structured pre-shipment inspection protocol. Physical inspection covers label integrity, firmware revision marking, connector pin condition, and housing for evidence of rework or counterfeit indicators. Each unit undergoes a functional power-on test confirming backplane enumeration, port link negotiation, and LED status sequence against the factory reference. Units are packed in anti-static bags with humidity indicator cards, placed in foam-lined cartons rated for international air freight handling per ISTA 2A.

Shipment from Xiamen is executed via DHL Express, FedEx International Priority, or UPS Worldwide Express, with typical transit times of 3–5 business days to Europe, North America, Southeast Asia, and the Middle East. Full export documentation is provided with every shipment: commercial invoice, packing list, certificate of origin (Form A or CO), and HS code declaration (HS 8537.10.9000). ECCN classification (EAR99 for standard configurations) is available on request for US import compliance. All units carry a 12-month warranty covering manufacturing defects and functional failure under normal operating conditions.

Contact Information

Email: [email protected]
WhatsApp: +86 18359268345
Web: siemensplc.com
Location: Xiamen, China
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