1756-EN4TR Process-Optimized Ethernet Bridge Replacement

Overview

The Allen-Bradley 1756-EN4TR is a high-performance, process-optimized EtherNet/IP communication module designed for the ControlLogix platform. Boasting gigabit capability, embedded Device Level Ring (DLR) functionality, and Parallel Redundancy Protocol (PRP) support, it serves as the modern backbone for complex automation architectures.

Whether you are performing a critical swap-out of a failed module on a live line or executing a plant-wide migration from legacy 10/100 Mbps communication bridges, precise installation and configuration are essential. A misconfigured network module can sever communications between the Programmable Automation Controller (PAC) and remote I/O chassis, variable frequency drives (VFDs), or supervisory control and data acquisition (SCADA) systems, resulting in immediate production downtime. This guide provides the complete, field-tested technical procedure for a seamless replacement process.

Legacy Product Information

For decades, modules such as the 1756-EN2TR and 1756-EN3TR served as the standard-bearer for dual-port ControlLogix EtherNet/IP communications. However, contemporary industrial systems demand significantly higher data throughput, enhanced industrial cybersecurity, and faster I/O connection speeds.

The 1756-EN4TR represents the latest evolution in this interface category, providing a substantial leap in packets-per-second capability and incorporating hardware-based cryptographic security (CIP Security).

Module Specification Comparison:

• 1756-EN2TR: Supports 10/100 Mbps Ethernet speeds. Connection capacity is limited to 256 Logix connections (128 TCP). Does not support gigabit speed, native CIP Security, or PRP. Status: Active/Mature.
• 1756-EN3TR: Dual-port 10/100 Mbps module primarily tailored for high connection counts (up to 256 Logix connections). Lacks gigabit physical layers and hardware-root security features. Status: Mature.
• 1756-EN4TR: Supports 10/100/1000 Mbps (1 Gbps) Ethernet speeds. Extremely high backplane capability supporting up to 1,000 TCP connections and 512 Logix connections. Native hardware support for DLR, PRP, and CIP Security. Status: Active (Current Standard).

Common legacy applications of these interface modules include distributed I/O control networks in water wastewater, oil and gas, and chemical processing facilities where continuous uptime is protected via dual-path rings.

Recommended Replacements

For maintenance managers and control engineers looking to upgrade or replace failing network hardware, the following table lists the recommended pathway for legacy ControlLogix communication bridges.

Compatibility Considerations

Before pulling a module out of a live chassis, there are several electrical, logical, and software factors that must be cross-referenced to prevent a system mismatch fault.

Footprint & Backplane Power Draw

The 1756-EN4TR features the standard single-slot form factor, making it physically compatible with all standard ControlLogix chassis (1756-A4, -A7, -A10, -A13, -A17, and standard XT counterparts). However, you must verify the backplane power supply budget:

• 1756-EN4TR Current Draw: 1.2 A @ 5.1V DC and 3 mA @ 24V DC.
• Note: Ensure that your overall chassis power supply (e.g., 1756-PA72 or 1756-PB75) has sufficient overhead to accommodate the minor increase in amp-draw compared to older legacy modules.

Connection and Cabling Infrastructure

The 1756-EN4TR features two RJ45 ports that support 10/100/1000 Mbps. If you are migrating a network from 100 Mbps to 1 Gbps, your physical infrastructure must be validated:

• Cabling: Ensure any existing Cat5 lines are upgraded to Cat5e or Cat6 to reliably maintain a Gigabit link rate.
• Network Switches: Verify that upstream industrial Ethernet switches can handle auto-negotiation or are manually set to accept 1 Gbps flow rates.

Software and Firmware Pre-requisites

• Studio 5000 Logix Designer: The 1756-EN4TR requires Studio 5000 version 32.00 or later to leverage its full capabilities (including PRP and CIP Security). If using older software versions, you may need to download the appropriate Add-On Profile (AOP).
• Electronic Keying: Pay close attention to the Offline Logix Designer project’s keying settings. If set to Exact Match, the replacement module's firmware must match the major and minor revisions configured in the software down to the decimal. Alternatively, set the keying parameter to Compatible Module to allow minor firmware variations.

Upgrade Benefits

Migrating from an older-generation EtherNet/IP bridge to the 1756-EN4TR yields immediate benefits in both data integrity and network performance:

1. Deterministic High-Speed Performance: By operating at 1 Gbps, network propagation delays are drastically minimized. This is critical for high-motion applications or highly distributed process automation applications utilizing extensive remote I/O drops.
2. Ultra-Resilient Network Topologies: With built-in support for Parallel Redundancy Protocol (PRP), the module can send identical packets simultaneously over two independent LAN pathways. If one path fails, the receiver processes the packet from the alternate path with zero-millisecond recovery time.
3. Industrial Cyber Security (CIP Security): The 1756-EN4TR helps guard against unauthorized device access, data tampering, and packet-sniffing attacks by validating device identity via cryptographic certificates and utilizing TLS and DTLS pathways.

                  +----------------------------------+
                  |       1756-EN4TR Module          |
                  |                                  |
                  |   [Port 1]            [Port 2]   |
                  +------+-------------------+-------+
                         |                   |
        +----------------v---+       +-------v------------+
        |   LAN A Pathway    |       |   LAN B Pathway    |
        | (Primary Active)   |       | (Secondary Active) |
        +----------------+---+       +-------+------------+
                         |                   |
                  +------v-------------------v-------+
                  |  Destination Node (PRP Enabled)  |
                  +----------------------------------+

Common Migration Challenges

• Firmware Mismatch ("Code 16#0114" Fault): If the Logix controller is programmed with an "Exact Match" keying configuration, inserting a new module with factory-default or slightly updated firmware will trigger a yellow warning icon in Studio 5000 with a Keying Mismatch error (Code 16#0114). Always flash the unit beforehand.
• IP Addressing Collisions: Utilizing DHCP/BOOTP on default settings without disabling the server capability after assignment can lead to the module losing its assigned IP address upon a control power cycle.
• Duplex and Speed Mismatches: If the switch port connecting to the module is hardcoded to 100 Mbps Full Duplex, and the new 1756-EN4TR is set to Auto-Negotiate, communication degradation or a total network drop may occur. Verify that both the module and switch port are configured symmetrically.

Step-by-Step Replacement Procedure

Follow these steps to safely swap a failed module or execute a hardware upgrade.

Step 1: Pre-Migration Backup and Parameter Recording

• Establish communications with the existing module and go offline with the Studio 5000 Logix project.
• Open the module properties. Record the exact custom IP Configuration (IP Address, Subnet Mask, Gateway) and write down the current firmware revision listed on the module’s General tab.

Step 2: Physical Extraction (Lockout/Tagout Considerations)

• Warning: While ControlLogix modules are technically "Hot-Swappable" (RIUP - Removal and Insertion Under Power), it is highly recommended to de-energize the host chassis if the replacement is being performed in a hazardous or safety-critical process environment.
• Unplug the Ethernet cables linked to ports 1 and 2, being careful to label their ports if utilizing a Device Level Ring (DLR) or PRP topology.
• Squeeze the top and bottom tabs of the old module and pull it straight out of the chassis slot.

Step 3: Preparing the New 1756-EN4TR Module

• Unpack the new module. If you are substituting an older module like the 1756-EN2TR, check that the slot orientation and guiding grooves align.
• The 1756-EN4TR features a front-panel USB Type B port and an alphanumeric status display. No physical DIP switches are used to set the IP address on this module.

Step 4: Installation and Firmware Configuration

• Slide the 1756-EN4TR module into the target slot and push until the latching tabs snap closed.
• Connect your PC to the front of the EN4TR via a standard USB cable.
• Open RSLinx Classic or FactoryTalk Linx on your workstation. Expand your USB driver to locate the newly connected module.
• Right-click the module, choose Configuration, and adjust the Ethernet port properties. Assign the static IP Address, Subnet Mask, and Gateway recorded in Step 1. Apply changes.
• Launch ControlFLASH or ControlFLASH Plus. Select the target module via the USB or Ethernet path. Flash the module’s firmware to match the revision dictated by your Studio 5000 project.

Step 5: Studio 5000 Configuration Adjustment (If Upgrading)

• If replacing an older model (e.g., swapping a 1756-EN2TR for a 1756-EN4TR), open your offline PLC project.
• Right-click the existing network module in the I/O Configuration tree, select Change, and update the module type to "1756-EN4TR". Alternatively, if keying settings permit, keep the module profile but update the communication options.
• Download the updated project to the main Controller and verify that all I/O connection indicators turn solid green.

Step 6: Post-Installation Validation

• Observe the front-panel scrolling display. A healthy unit will scroll the dynamic IP address along with "OK" status messages.
• Perform a continuous ping test from your workstation to check network consistency: ping -t [Module_IP]. Ensure there are zero dropped packets over a 5-minute window.

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Frequently Asked Questions

Q1: Can I replace a 1756-EN2TR with a 1756-EN4TR without modifying my Studio 5000 Logix project?
A1: Yes. You can run the 1756-EN4TR in a legacy emulation mode or set the electronic keying in your configuration to "Disable Keying" if you cannot instantly modify the project, though updating the controller's I/O tree to match the actual 1756-EN4TR hardware profile remains best practice.

Q2: How do I hardcode the speed and duplex settings on the 1756-EN4TR?
A2: This is managed via Studio 5000 or through the module's embedded web server. Go to the Module Properties in RSLinx or Logix Designer, navigate to the Port Diagnostics tab, and configure the Speed/Duplex parameters from "Auto-Negotiate" to your specific manual requirements (e.g., 100 Mbps Full Duplex).

Q3: The scrolling display says "BOOTP/DHCP Enabled" and I keep losing my IP. How do I lock it?
A3: In RSLinx, right-click the module, choose Module Configuration, go to the Network tab, and toggle the radio button from "BOOTP/DHCP" to "Static". Alternatively, you can use the Rockwell BOOTP/DHCP utility and select "Relation -> Disable BOOTP/DHCP" once the module takes an address.

Q4: What happens if I insert a Series B module when my project was designed for a Series A?
A4: Under a "Compatible Module" keying setting, logix controllers will interact with the module without issue. Under "Exact Match", the controller may generate a connection fault. Update your Add-On Profile (AOP) in Studio 5000 to resolve this mismatch.

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Related Products & Families

To complete your network architecture and ensure compatibility across your Allen-Bradley ControlLogix automation rack, consider utilizing these corresponding product lines:

• ControlLogix Control Systems: 1756-L81E, L82E, L83E, L84E Series Controllers.
• Chassis and Chassis Accessories: 1756-A4, 1756-A7, 1756-A10, and 1756-A17 backplanes.
• ControlLogix Power Supplies: Standard 1756-PA72 and 1756-PB72 units, or redundant series (1756-PSCA2).

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Need Help?

Replacing or upgrading critical industrial network modules requires precision engineering to prevent unexpected control failures. If you need technical assistance, replacement parts, or hard-to-find components, Palm Parts Solution can help. We can supply new, refurbished, or surplus units with a comprehensive warranty to get your systems back up and running quickly. Contact our North American support team for immediate quotes and inventory availability.