Description
Product Introduction
The Allen-Bradley 1756-EN2T is a ControlLogix EtherNet/IP communication module used to connect ControlLogix processors, remote I/O racks, HMIs, drives, and industrial devices through standard Ethernet infrastructure. It provides a single 10/100 Mbps copper Ethernet interface and supports EtherNet/IP messaging, I/O communication, and controller-to-controller data exchange.
In our field experience, the 1756-EN2T became a common replacement for older Ethernet communication modules such as the 1756-ENBT because of its increased connection capacity and improved communication performance. It remains widely installed in production systems. The limitation is not the module itself; it is usually the surrounding network design, switch configuration, and outdated firmware management practices.
Key Technical Specifications
| Parameter | Value |
|---|---|
| Manufacturer | Allen-Bradley / Rockwell Automation |
| Catalog Number | 1756-EN2T |
| Product Family | ControlLogix |
| Module Type | EtherNet/IP Communication Module |
| Communication Protocol | EtherNet/IP |
| Ethernet Interface | 1 × RJ45 Copper Port |
| Ethernet Speed | 10/100 Mbps |
| Ethernet Standard | IEEE 802.3 |
| TCP Connections | 128 maximum |
| CIP Connections | 256 maximum |
| CIP Unconnected Messages | 128 + 128 (backplane + Ethernet) |
| Communication Cable | Category 5 twisted pair Ethernet |
| Slot Requirement | 1 ControlLogix slot |
| Backplane Current Draw | 1.0 A @ 5.1 VDC / 3 mA @ 24 VDC |
| Power Dissipation | 5.1 W |
| Isolation Voltage | 30 V continuous Ethernet-to-backplane isolation |
| Mounting | ControlLogix chassis |
| Software Support | RSLogix 5000 / Studio 5000 Logix Designer |
| Operating Temperature | 0°C to +60°C |
| Lifecycle Status | Active |
Application Scenarios & The “Trench” Experience
A production line stops communicating.
The controller is running. The I/O modules look normal. The HMI screen freezes. A technician immediately suspects the PLC program.
That is usually the wrong place to start.
The 1756-EN2T sits between the ControlLogix backplane and the Ethernet network. IP settings, switch configuration, Ethernet cables, duplicate addresses, and connection limits all matter.
Typical applications include:
- Automotive Manufacturing – Robot cell communication – The 1756-EN2T provides EtherNet/IP connectivity between ControlLogix controllers, remote racks, drives, and HMIs.
- Packaging Equipment – Machine control networks – Supports communication with PanelView terminals, PowerFlex drives, and distributed I/O.
- Process Automation – Plant-wide data exchange – Connects controllers with SCADA systems, historians, and engineering workstations.
- Water Treatment – Remote control stations – Provides Ethernet communication between central controllers and remote ControlLogix chassis.
- OEM Machinery – Standardized automation platforms – Allows machine builders to integrate Ethernet-based devices into ControlLogix architectures.
Field Case
A food processing facility experienced intermittent HMI communication failures on a ControlLogix system using a 1756-EN2T.
The first replacement attempt involved swapping the communication module.
The fault returned.
The real issue was a duplicate IP address created after a maintenance laptop was temporarily connected to the plant network. The 1756- was operating correctly. The network configuration was not.
After correcting the IP allocation process and documenting device addresses, the system remained stable.
Transparency SOP: Quality Assurance & Testing
We don’t just ship boxes; we test them on actual Allen-Bradley ControlLogix racks
- Inbound Inspection
- Verify Allen-Bradley label, catalog number, series, and hardware revision.
- Inspect RJ45 Ethernet port, USB port (if applicable), and backplane connector.
- Check for corrosion, physical damage, and unauthorized repairs.
- Live Rack Testing
- Install module in a ControlLogix chassis.
- Verify recognition through Studio 5000 Logix Designer.
- Assign test IP address.
- Confirm EtherNet/IP communication with a controller and test device.
- Electrical Parameter Checks
- Measure backplane current consumption.
- Verify Ethernet link status.
- Check module diagnostics and communication indicators.
- Firmware Verification
- Record exact firmware revision.
- Confirm compatibility with existing Studio 5000 projects.
- Verify EDS/AOP identification data.
- Final QC & Anti-static Packaging
- Complete communication testing.
- Protect Ethernet connector and backplane contacts.
- Package with anti-static protection.
The Veteran’s Tech Trap Guide
⚠️ Do not swap an without recording the IP address first. A replacement module with the wrong address can create a plant-wide communication problem.
❗ Check the Studio 5000 module profile. Firmware mismatch between the project and communication module can cause connection faults during download.
⚠️ Do not blame the module before checking the network switch. Port settings, VLAN configuration, cable faults, and duplicate IP addresses create symptoms that look like hardware failure.
⚠️ Watch the connection count. A busy supporting multiple HMIs, historians, remote I/O racks, and controllers can hit connection limits if the architecture was never planned.
⚠️ Verify firmware before replacing older ENBT modules. The physical installation may look similar, but communication settings and project configuration require review.
Take a screenshot of the Ethernet module properties before pulling the old card. Trust me. That screenshot can save hours during commissioning.
Frequently Asked Questions (FAQ)
Q1. What is the Allen-Bradley 1756-?
The is a ControlLogix EtherNet/IP communication module that provides Ethernet connectivity for ControlLogix automation systems.
Q2. What is the difference between 1756- and 1756-ENBT?
The 1756- is a newer EtherNet/IP communication module with higher connection capacity and improved communication performance compared with the older 1756-ENBT. Migration still requires checking firmware, project configuration, and network design.
Q3. Does the 1756- have dual Ethernet ports?
No. The standard has one RJ45 Ethernet port. For dual-port or redundancy applications, engineers typically evaluate other models such as the 1756-EN2TR family.
Q4. Can the 1756- communicate with remote ControlLogix I/O racks?
Yes. A 1756- can be used in ControlLogix architectures where EtherNet/IP communication is required between chassis and distributed I/O systems.
Q5. Can the 1756- be hot-swapped?
ControlLogix supports removal and insertion under certain configured conditions, but the procedure depends on the system design and application requirements. Always follow Rockwell Automation installation procedures before removing an energized module.
Q6. Why is a surplus 1756- cheaper than buying directly from Rockwell Automation?
Industrial automation surplus units usually come from plant spare inventory, excess stock, equipment retirement, or system upgrades. The key question is whether the module has been tested, not simply whether it is labeled as unused.
Q7. Is the 1756- still available?
Yes. Rockwell Automation lists the 1756- EtherNet/IP communication module as an active product.
Q8. What warranty is typically provided?
Qualified automation suppliers commonly provide a 12-month warranty on tested new surplus and refurbished 1756- modules. Warranty terms should always be confirmed before purchase.
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