Allen-Bradley 1756-EN2T/B ControlLogix EtherNet/IP Bridge Module

The 1756-EN2T/B is a high-capacity EtherNet/IP communication bridge module manufactured by Allen-Bradley, a brand of Rockwell Automation, and is a cornerstone member of the Bulletin 1756 ControlLogix family of programmable automation controllers. Designed to serve as the interface between the ControlLogix backplane and an EtherNet/IP network, the 1756-EN2T/B gives the controller the ability to communicate natively with a wide range of industrial devices — including remote I/O adapters, variable frequency drives, HMI terminals, SCADA servers, and peer controllers — using the same producer/consumer CIP messaging model that underpins the entire Logix platform. This unified communication architecture means that a single 1756-EN2T/B can simultaneously carry cyclic I/O data, explicit messages, and controller-to-controller tag sharing without the need for protocol gateways or separate network hardware.As the direct successor to the legacy 1756-ENBT, the 1756-EN2T/B represents a substantial step up in processing capacity and connection handling. Where the ENBT was limited to 128 CIP connections, the 1756-EN2T/B supports up to 256 CIP connections and 128 TCP connections, with a packet-handling capability roughly twice that of its predecessor. This additional headroom is what allows the module to serve both a large I/O count and a meaningful number of HMI clients and MSG instructions at the same time — a balance that the ENBT could not reliably strike. Series B of the 1756-EN2T/B also introduced practical configuration conveniences, including a front-panel USB 1.1 port for direct PC access and rotary thumbwheel switches for quick IP address setup, both of which reduce the time required to commission or replace a module in the field. Drawing 1 A at 5.1 V DC from the backplane and dissipating 5.1 W, the module occupies a single chassis slot and carries the same open-style enclosure and 0–60 °C rating as the rest of the ControlLogix family, making it a straightforward drop-in for both new designs and brownfield upgrades.

Category: A-B

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Description

Technical Specifications

Parameter Name	Parameter Value
Product Model	1756-EN2T/B
Manufacturer	Allen-Bradley (Rockwell Automation)
Product Type	ControlLogix EtherNet/IP Bridge Module
Network Protocol	EtherNet/IP (CIP over TCP/UDP/IP)
Ethernet Ports	2 × RJ-45, Category 5, 10/100 Mbps auto-negotiating
Communication Rate	10/100 Mbps, half/full duplex
Max TCP Connections	128
Max CIP Connections	256 (usable for any combination of explicit or implicit applications)
CIP Unconnected Messages	128 (backplane) + 128 (Ethernet)
I/O Packet Rate	Up to 10,000 packets per second
HMI/MSG Packet Rate	Up to 3,200 packets per second
IP Configuration	Static, DHCP, or BOOTP; thumbwheel switches and USB port for setup
Backplane Current (5.1 V DC)	1 A
Backplane Current (24 V DC)	3 mA
Power Dissipation	5.1 W
Thermal Dissipation	17.4 BTU/hr
Isolation Voltage	30 V continuous (basic insulation), Ethernet/USB to backplane; type-tested at 980 V AC for 60 s
Enclosure Type	Open style (chassis-mounted)
Slot Width	1 slot
Module Location	Any slot in a 1756 ControlLogix chassis
Compatible Chassis	1756-A4, 1756-A7, 1756-A10, 1756-A13, 1756-A17
Dimensions (W × H × D)	35 × 145 × 140 mm (1.3 × 6.0 × 5.5 in)
Weight	Approximately 0.2 kg (5.6 oz)
Operating Temperature	0–60 °C (32–140 °F)
Storage Temperature	–40–85 °C (–40–185 °F)
Relative Humidity	5–95% RH, non-condensing
EMI Immunity	Conducted RF 10 V rms; EFT/B ±3 kV; ESD 6 kV contact / 8 kV air
Emissions	CISPR 11 Class A
Certifications	cULus, CE, C-Tick, KC, ATEX Zone 2, SIL 2 capable (per configuration)
Supported Software	Studio 5000 / RSLogix 5000 (v15.00+), RSLinx Classic (v2.51+), ControlFLASH (v4.0+)

Main Features and Advantages

Twice the capacity of the module it replaced: The 1756-EN2T/B was engineered as the ENBT’s successor, and the improvement is not incremental. With 256 CIP connections and 128 TCP connections, the module can carry a large remote I/O population while still leaving capacity for HMI clients, SCADA polling, and inter-controller messaging. In practical terms, this means an application that would have required two ENBT modules — or a painful reduction in I/O count — can be handled by a single 1756-EN2T/B. The doubled packet-handling capability also prevents the module from becoming the bottleneck when a line is expanded with additional drives or a second HMI is added to the same network.Dual-port architecture without external switching: The two RJ-45 ports on the 1756-EN2T/B function as an embedded switch, allowing the module to support linear, star, and Device Level Ring topologies without an external Ethernet switch. For a brownfield plant, this is the difference between running a new home-run cable to a central switch and simply extending the existing trunk to the next device. Port 1 can be configured as a DLR ring supervisor or ring node while Port 2 operates as an independent linear or star connection, enabling a phased modernization in which the new ring coexists with the old linear infrastructure until the cutover is complete.Configuration that survives a service call: Series B brought two features that materially reduce commissioning and replacement time: a USB 1.1 port for direct connection to a PC, and rotary thumbwheel switches that set the module’s IP address without software. A technician can walk up to a 1756-EN2T/B, read or set the address on the switches, and have the module online in minutes — no laptop, no RSLinx browse, no IP conflict. Once the module is in the I/O tree, its configuration is stored with the controller project, so a hot-swapped replacement inherits the correct settings automatically.Diagnostic visibility at the cabinet door: The front-panel status LEDs report link state, activity, module health, and network status as distinct indications, allowing a technician to distinguish a dead port, a lost connection, and a module fault without opening a browser. SNMP support and the onboard web server extend that visibility to the enterprise network, where a network management system can poll the 1756-EN2T/B for connection counts, packet statistics, and fault history as part of routine asset monitoring.