Allen-Bradley 1756-EN2TXT/B ControlLogix EtherNet/IP Communication Module

The Allen-Bradley 1756-EN2TXT/B, also cataloged as the 1756-EN2TXT/B EtherNet/IP communication module, operates as a dedicated high-speed bridge component for CIP packet routing within ControlLogix backplane networks.
Configured for deterministic Ethernet data exchange in ControlLogix chassis systems, the Allen-Bradley 1756-EN2TXT/B (1756-EN2TXT/B communication module) provides direct backplane-to-EtherNet/IP transmission with embedded switching and redundancy-aware session handling.

Suffix Breakdown & Model Matrix

• 1756: ControlLogix chassis platform family

• EN2TXT: Dual-port EtherNet/IP communication bridge with embedded switch architecture

• /B: Hardware revision level indicating updated internal processing and firmware baseline compatibility

Hardware Specifications

EtherNet/IP Backplane Routing & Embedded Switch Deterministic Behavior

The module executes CIP object routing between ControlLogix backplane tasks and external Ethernet nodes through an integrated dual-port switching fabric.
Backplane communication is scheduled through chassis arbitration, ensuring deterministic delivery of Logix-class connections under mixed I/O and messaging loads.

Embedded switch logic maintains frame forwarding between RJ45 ports without external switching hardware, enabling linear and star topology segmentation.
Redundant controller configurations mirror connection tables at the CIP layer, with session reestablishment handled through backplane synchronization after failover events.

Firmware revision /B aligns internal processing timing with updated Logix stack behavior, reducing connection renegotiation latency during controller scan transitions.

Frequently Asked Questions (FAQ)

Q: Can the 1756-EN2TXT/B be hot-inserted into an energized ControlLogix chassis?
A: Yes. The module supports hot-swap insertion. The backplane performs automatic module re-enumeration after slot detection.

Q: What is the impact of Ethernet traffic on backplane current draw?
A: The module maintains a fixed backplane load of approximately 1 A at 5 VDC. Network traffic does not modify power consumption.

Q: How does redundancy affect CIP connection continuity?
A: In redundant controller architectures, CIP sessions are replicated across controllers. Failover triggers automatic session rebind through backplane synchronization.

Field Installation Guidelines

Insert the module into a valid 1756 ControlLogix chassis slot with full backplane engagement. Improper seating can result in intermittent CIP communication loss or module fault states.

Use shielded twisted-pair Cat 5 or higher Ethernet cabling. Ensure shield termination at the cabinet entry ground point to minimize EMI coupling into high-speed differential pairs.

Maintain separation between Ethernet routing and high-current conductors such as motor drives or switching power lines. Cross at 90 degrees when unavoidable.

Verify firmware alignment between controller, chassis, and communication module before commissioning. Mismatched revisions may cause connection table inconsistencies during runtime transitions.