Allen Bradley 1756-EN2T 1756-EN3TR 1756-RIO 1756-CN2R 1756-ENBT ControlLogix Communication Modules

The Allen-Bradley 1756 ControlLogix communication modules establish high-speed, deterministic network connections across the Logix5000 industrial architecture. Operating within a standard ControlLogix chassis, these modules act as network gateways and bridges, routing I/O data, peer-to-peer interlocking messages, and diagnostics without draining the central CPU's processing power. They provide the network flexibility required for standard, redundant, and high-availability automation systems.
We maintain a comprehensive inventory of brand-new, factory-sealed Allen-Bradley 1756 communication modules, complete with a 1-year factory warranty. Whether you are executing a system modernization, expansion, or seeking safety-critical replacements, our technical team can verify module compatibility and firmware alignment prior to shipment.

Compatibility & System Notice:

When replacing End-of-Life modules like the 1756-ENBT or 1756-RIO, hardware series and firmware revision compatibility must be cross-referenced with the existing Logix controller project to ensure seamless slot integration. Migrating across these distinct network families typically requires architectural reconfiguration of the I/O tree within the programming software.

• Network Architecture Capability: Configurable as local/remote I/O scanners or messaging adapters; supports non-blocking CIP routing across backplanes without draining CPU processor bandwidth.
• Environmental & Electrical Safety: Compliant with c-UL-us, CE, UKCA, RCM, Ex, and KC standards; features built-in ESD protection and electrical isolation per industrial network specifications.
• Hazardous Location Ratings: Meets Class I, Division 2, Groups A, B, C, D T4A/T5, and ATEX/IECEx Zone 2 requirements for flammable gas, vapor, or mist environments.
• Functional Redundancy: Native hardware support for physical media fault-tolerance via Dual-Port EtherNet/IP (DLR topology) and dual coaxial BNC ControlNet architectures.

EtherNet/IP Series (1756-EN2T / 1756-EN3TR)：

• Protocol & Bandwidth: Built on standard TCP/IP and UDP/IP (10/100 Mbps). It uses an unscheduled, event-driven model optimized for high-capacity I/O, HMI data, and peer-to-peer interlocking.
• Data Prioritization: Relies on Quality of Service (QoS) packet prioritization. Time synchronization requires application-layer CIP Sync (IEEE 1588).
• Media Redundancy: Employs RJ45 copper or fiber media in star, linear, or ring layouts. Dual-port modules (1756-EN3TR) utilize logical Device Level Ring (DLR) topology for network fault tolerance.

ControlNet Series (1756-CN2R)：

• Protocol & Bandwidth: Utilizes a scheduled, token-passing protocol at a fixed 5 Mbps. It eliminates packet collisions by dividing traffic into strictly timed Scheduled and Unscheduled bands.
• Data Prioritization: Guarantees absolute, repeatable determinism for critical control loops and safety data. Time synchronization is executed natively via hardware-level Coordinated System Time (CST).
• Media Redundancy: Built on an RG-6 coaxial trunkline architecture. The module features dual BNC ports providing physical, bit-level hardware media redundancy across two concurrent channels.

 

Key specs (all ENx series modules)

• Chassis Slot Occupancy: 1 standard ControlLogix 1756 slot.
• Backplane Power: Draws power directly from +5.1V DC and +24V DC lines.
• Maintenance Capability: Removal and Insertion Under Power (RIUP) supported for online replacement.
• Protocol Core: Built on the Common Industrial Protocol (CIP) architecture.
• Operating Temperature: 0°C to +60°C (32°F to +140°F).
• Relative Humidity: 5% to 95% non-condensing.
• Vibration & Shock: 2 g operational vibration at 10...500 Hz; 30 g operational shock.

The matrix below provides a definitive technical breakdown of key 1756 communication modules, including data rates, maximum connection capacities, and backplane power consumption variables.

Product Image	Catalog Number	Data Rate	Max Connections / Capacity	Backplane Current Draw	Power Dissipation	Physical Ports	Action
	1756-ENBT	10/100 Mbps	128 CIP connections 64 TCP/IP connections	700 mA @ 5.1V DC 0 mA @ 24V DC	3.7 W	1 x RJ45 port	Inquire Now!
	1756-EN2T	10/100 Mbps	256 CIP connections 128 TCP/IP connections	1.0 A @ 5.1V DC 3 mA @ 24V DC	5.1 W	1 x RJ45 port 1 x USB port (configuration only)	Inquire Now!
	1756-EN3TR	10/100 Mbps	256 CIP connections 128 TCP/IP connections	1.2 A @ 5.1V DC 3 mA @ 24V DC	6.2 W	2 x RJ45 ports (DLR supported) 1 x USB port (configuration only)	Inquire Now!
	1756-CN2R	5 Mbps	100 ControlNet connections	1.3 A @ 5.1V DC 3 mA @ 24V DC	6.6 W	2 x BNC coaxial ports (redundant) 1 x NAP port; 1 x USB port	Inquire Now!
	1756-RIO	57.6 Kbps / 115.2 Kbps / 230.4 Kbps	32 logical racks	450mA @ 5.1V DC 5 mA @ 24V DC	2.5 W	1 x 3-pin DH+/RIO terminal block 1 x USB port (configuration only)	Inquire Now!

Technical Note: Max connection limits and power dissipation variables are catalog-specific and directly scale based on network media and port configurations. Firmware revisions must be matched to controller project requirements to ensure full capacity utilization.

ControlNet Modules provides a fixed bandwidth of 5 Mbps and fully deterministic network scheduling. Before the widespread adoption of Ethernet technologies (EN2T/EN3TR), ControlNet was the standard backbone control network for ControlLogix systems.The following is a list of information regarding the ControlNet (CNx Series) Extended Product Matrix：

Technical Note: Classic modules (1756-CNB/CNBR) are capped at 64 connections, whereas the newer CN2 architecture doubles that limit to 128 connections while adding support for modern USB configuration interfaces.

The matrix below provides a definitive technical breakdown of key 1756 Remote I/O communication modules, including data rates, maximum connection capacities, and backplane power consumption variables.

Technical Note: The 1756-RIO series operates strictly as a legacy migration path, limited to old-style block transfers and a max baud rate of 230.4 Kbps to facilitate phased upgrades of legacy PLC-5 or SLC 500 field hardware.

Technical Note: The architecture demonstrates full consolidation into EtherNet/IP, with ControlNet and RIO hardware capping development at Generation 2 for legacy maintenance.

• Upper-Layer Protocol: 100% dependency on the Common Industrial Protocol (CIP) for data structuring and cross-network messaging.
• ControlLogix Backplane Routing: 0% load on the central controller CPU for data bridging across the 1756 backplane slots.
• Data Distribution Model: Producer/Consumer multicast mechanism for simultaneous data delivery to multiple nodes from a single transmission packet.
• System Integrity Control: 3 levels of software-enforced Electronic Keying (Exact Match, Compatible Module, Disabled Keying) to block incorrect hardware installation.
• Live System Maintenance: Removal and Insertion Under Power (RIUP) capability, allowing hot-swapping under full chassis power.
• Environmental Boundaries: Operation from 0°C to +60°C (32°F to +140°F), 5% to 95% non-condensing relative humidity, 2 g operational vibration at 10 to 500 Hz, and 30 g operational shock.

Security Architecture (CIP Security)

• Data Integrity (HMAC): Uses cryptographic hashing to verify that transmitted packets are authentic and have not been altered.
• Payload Encryption (TLS/DTLS): Encrypts network traffic to prevent unauthorized data interception and viewing.
• Identity Verification (X.509): Employs digital certificates and cryptographic keys to restrict network connections strictly to trusted devices.

Redundant Operations

Redundancy configurations vary by network type to maintain high availability and prevent single points of failure:
EtherNet/IP Device Level Ring (DLR): Modules with dual ports (e.g., 1756-EN2TR, 1756-EN3TR) natively support DLR topology. If a single point in the network ring breaks, the modules automatically reroute traffic in less than 3 milliseconds, maintaining continuous I/O communication.
ControlNet Media Redundancy: Modules designated with an "R" suffix (e.g., 1756-CN2R, 1756-CNBR) feature dual BNC coaxial ports (Channel A and Channel B). Data is transmitted simultaneously across both cables. If one cable is damaged, the module instantly switches to the healthy channel with zero data loss.
ControlLogix System Redundancy: EtherNet/IP and ControlNet modules fully support inclusion in a synchronized, dual-chassis ControlLogix Redundancy System (using 1756-RM2 modules). The communication modules mirror their internal state connection tables from the primary chassis to the secondary chassis, allowing an invisible switchover if the primary chassis fails.

A ControlLogix® system uses connections to establish communication links between devices. The types of connections include the following:

• Controller-to-local I/O modules or local communication modules
• Controller-to-remote I/O or remote communication modules
• Controller-to-remote I/O (rack-optimized) modules
• Produced and consumed tags
• Messages
• Controller access with the Studio 5000® environment
• Controller access with RSLinx® software for HMI or other applications

You indirectly determine the number of connections the controller uses by configuring the controller to communicate with other devices in the system. The communication module you use defines the connection limit. If a message path routes through a communication module, the connection that is related to the message also counts towards the connection limit of that communication module.

Key Migration & Upgrade Notes:

• Form-Factor Compatibility: All replacement models maintain 100% physical compatibility with standard 1756 ControlLogix chassis slots. No hardware backplane changes are necessary.
• Electronic Keying Adjustments: When swapping a legacy module (e.g., 1756-ENBT) for a newer generation (e.g., 1756-EN2T), the module definition within the Studio 5000 programming software must be updated to reflect the new catalog number and correct electronic keying profile.
• Network Medium Transitions: Migrating from ControlNet or RIO to EtherNet/IP is highly recommended by Rockwell Automation, as Generation 3 EtherNet/IP modules (EN4TR) deliver the speed, security, and bandwidth required for modern control architectures.

Hardware Status Indicators (LED & Display)

EtherNet/IP:

• RUN: Green = Operational; Off = No power/boot failure.
• NET: Green = Active CIP connections; Flashing Green = Valid IP, no active connections; Flashing Red = Connection timeout; Red = Duplicate IP detected.
• OK: Green = Healthy; Flashing Red = Recoverable fault (firmware mismatch); Red = Unrecoverable hardware failure.

ControlNet:

• OK: Identical to EtherNet/IP baseline.
• Channel A / B: Green = Normal; Flashing Red/Green = Bad frame/media config mismatch; Red = Physical media fault or total packet loss.

Software & Programmatic Diagnostics

Studio 5000 Diagnostic Tabs:

• Module Info: Displays real-time status, serial number, firmware revision, and fault codes.
• Network/Diagnostics: Tracks media counters (In/Out Packets) and physical layer errors (FCS Errors, Alignment Errors, Collisions).

GSV Instruction Integration:
Real-time connection status can be read programmatically using the Get System Value (GSV) instruction pointing to the Module Object, attribute EntryStatus.

The upper 4 bits (Bits 12–15) decode as follows:

Embedded Web Server (EtherNet/IP Only)

Accessible via the module's IP address using a standard web browser:

• Connection Table: Lists active CIP connections, target IP addresses, types (I/O vs. Messaging), and RPI rates.
• Ethernet Statistics: Monitors bandwidth utilization, packet error counters, and port speed negotiation (100 Mbps / 1 Gbps).
• CIP Counters: Tracks explicit message failure counts to identify buffer overloads.

Network Capabilities & Device Messaging

The Data Highway Plus (DH+) network supports messaging, peer-to-peer data exchange, and programming links between controllers, computers, and HMIs. Concurrently, the Remote I/O (RIO) link is dedicated to real-time, deterministic communication between controllers and remote I/O chassis or other intelligent field devices.

1756-DHRIO Module Functionality / 1756-DHRIO

The 1756-DHRIO module serves as the physical interface connecting a ControlLogix® chassis to DH+ networks and RIO links. Each channel on the module can be independently configured:

• DH+ Channel: Supports messaging paths and routing between networks.
• RIO Channel (Scanner Mode): Actively scans and controls remote I/O adapter modules and chassis.
• RIO Channel (Adapter Mode): Allows the ControlLogix chassis to act as a remote I/O subscriber to another supervisory controller.

We stock the following 1756 communication modules (new, factory sealed):

• 1756-EN2T, 1756-EN2TR, 1756-EN3TR, 1756-EN4TR, 1756-ENBT, 1756-EN2TXT
• 1756-CN2, 1756-CN2R, 1756-CNB, 1756-CNBR, 1756-CN2/C, 1756-CN2RXT, 1756-CNBR/D, 1756-CNBR/E
• 1756-RIO, 1756-DHRIO

All units include:

• Original Allen-Bradley packaging
• Clear product status report (date code, firmware version if available)
• 1-year warranty

Lead time: Same-day processing for in-stock items. Shipping via DHL, UPS, or FedEx.

Contact now

Need help verifying firmware compatibility or safety certification requirements?

• Email: sales7@apterpower.com
• WhatsApp: +86 180 3017 5807
• Response time: < 2 hours during business hours (GMT+8)