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3. Key Technical Specifications
| Parameter | Value |
|---|---|
| Catalog Number | 1756-EN2TR |
| Module Type | EtherNet/IP communication module (dual copper ports) |
| Ethernet Ports | 2 × RJ45 (10/100 Mbps, auto-negotiate) |
| USB Port | 1 × USB 1.1 (programming only) |
| Supported Topologies | Linear, Device Level Ring (DLR) |
| TCP Connections, Max | 128 |
| CIP Connections, Max | 256 |
| Integrated Motion Axes, Max | 8 |
| Backplane Current @ 5.1 V DC | 1 A |
| Backplane Current @ 24 V DC | 3 mA |
| Power Dissipation, Max | 5.1 W |
| Thermal Dissipation | 17.4 BTU/hr |
| Isolation Voltage | 30 V continuous, basic insulation (Ethernet to backplane) |
| Slot Width | 1 |
| Module Location | Any slot in 1756 chassis |
| Compatible Chassis | 1756-A4, A7, A10, A13, A17 |
| Operating Temperature | 0…60 °C (32…140 °F) |
| Storage Temperature | –40…85 °C (–40…185 °F) |
| Relative Humidity | 5…95 % non-condensing |
| Enclosure Type | None (open-style) |
4. Product Introduction
The Allen-Bradley 1756-EN2TR is a dual-port EtherNet/IP communication module for ControlLogix systems. It provides two RJ45 ports with an embedded switch, supporting both linear and Device Level Ring (DLR) topologies for higher network availability.
The module handles up to 128 TCP and 256 CIP connections and supports a maximum of eight integrated motion axes. It installs in any slot of a standard 1756 chassis and draws 1 A at 5.1 V DC. Plants use it for distributed I/O, controller-to-controller messaging, HMI connectivity, and motion applications that require a dual-port copper interface with ring capability.
1756-EN2TR
1756-EN2TR
5. Troubleshooting Quick Reference
| Symptom | Possible Cause | Relevance to this Part | Quick Check Method | Recommendation |
|---|---|---|---|---|
| No link lights on either port | Cable, switch, or power issue | ❌ Low | Verify chassis power and try known-good Cat5e cable | Check network media and switch first |
| OK LED flashing red | Recoverable fault or configuration error | ✅ High | Connect via USB or Ethernet and read module diagnostics | Clear fault, verify IP address and electronic keying |
| OK LED solid red | Major fault | ✅ High | Cycle power and re-check diagnostics | Replace module if fault persists after power cycle |
| DLR ring fails to form | Incorrect ring supervisor or cabling | ✅ High | Confirm one supervisor is enabled and both ports linked | Verify ring topology and supervisor settings |
| High connection count faults | Exceeded 128 TCP or 256 CIP limit | ✅ Medium | Monitor connection usage in Logix software | Reduce connections or add another EN2TR module |
| Module not recognized in chassis | Bent backplane pins or wrong series | ✅ Medium | Inspect connector and confirm compatible chassis | Reseat module or replace if pins are damaged |
If the module still will not communicate after these checks, capture the exact status indicators, firmware revision, and diagnostic codes, then contact technical support with photos of the faceplate and network wiring.
6. Frequently Asked Questions (FAQ)
Q: What is the difference between the 1756-EN2TR and 1756-EN2T?
A: The EN2TR has two Ethernet ports and an embedded switch that supports Device Level Ring (DLR). The EN2T has a single port and does not support DLR.
Q: Can I use the 1756-EN2TR for integrated motion?
A: Yes. It supports up to eight axes of integrated motion on EtherNet/IP when used with a compatible ControlLogix controller and motion instructions.
Q: Do I need a special cable for the dual ports?
A: Standard Cat5e or better shielded or unshielded twisted-pair cable works. For DLR, both ports must be connected in a ring with proper supervisor configuration.
Q: Is the USB port for network traffic?
A: No. The USB port is for temporary programming and diagnostics only. It is not a network interface.
Q: Can this module be used in a redundant ControlLogix system?
A: Yes. The dual-port design and DLR support make it suitable for high-availability architectures. Confirm firmware compatibility with your controller revision.
Q: What happens if I exceed the connection limits?
A: The module will refuse additional connections. Monitor TCP and CIP connection counts in the controller diagnostics and redistribute load if needed.
Q: Is the 1756- still in active production?
A: Yes. It remains a current ControlLogix communication module. New original and new-surplus units are available.
