Allen-Bradley 1756-EN2TXT ControlLogix Communication Module

The Allen-Bradley 1756-EN2TXT, also cataloged as the 1756-EN2TXT High Performance Bridge w/ Embedded Switch module, operates as a dedicated Ethernet communication interface for Logix controller data exchange within ControlLogix chassis networks.
Configured for high-density CIP routing in ControlLogix systems, the Allen-Bradley 1756-EN2TXT (1756-EN2TXT communication module) provides direct backplane-to-EtherNet/IP packet bridging with dual-port embedded switching and deterministic connection handling.

Hardware Specifications

ControlLogix Backplane Communication & EtherNet/IP Switching Behavior

The module integrates into the ControlLogix backplane arbitration bus, executing CIP routing between Logix tasks and Ethernet endpoints.
Embedded switch logic enables internal frame forwarding between dual RJ45 ports, reducing external switching dependency in linear and star topologies.

Logix connection handling is segmented into scheduled and unscheduled traffic pools, with 256 Logix-class connections mapped to controller task execution threads.
TCP/IP stack allocation supports 128 concurrent sessions for diagnostics, HMI traffic, and configuration services.

Firmware compatibility must align with ControlLogix chassis revision to maintain stable connection tables and prevent CIP session renegotiation during controller scan updates.

Frequently Asked Questions (FAQ)

Q: Does the 1756-EN2TXT support hot insertion in an energized ControlLogix chassis?
A: Yes. The module supports hot-swap insertion. Backplane rescan occurs after slot initialization and module identity validation.

Q: How is backplane power distributed during peak Ethernet traffic?
A: The module maintains a fixed draw of 1 A at 5.1 VDC. Ethernet load does not alter backplane current consumption.

Q: What limits apply to TCP/IP and Logix connections simultaneously?
A: The module supports up to 256 Logix connections and 128 TCP/IP sessions. Allocation is handled independently per protocol stack.

Field Installation Guidelines

Insert the module into any available ControlLogix chassis slot with proper backplane alignment. Ensure connector seating is fully engaged to avoid intermittent CIP communication faults.

Use shielded Cat 5 Ethernet cabling for both RJ45 ports. Maintain consistent shield termination at cabinet entry point to reduce EMI coupling on high-speed 10/100 Mbps links.

Avoid routing Ethernet cables parallel to high-current motor or drive conductors. Maintain separation to prevent induced noise on differential pairs.

Verify firmware compatibility between controller, chassis, and communication module before commissioning. Mismatched revisions may cause connection reset cycles during runtime.