1756-ENBT end of life — replace with 1756-EN2T, EN2TR or EN4TR?

Status of the 1756-ENBT

The 1756-ENBT is a single-port EtherNet/IP module for the ControlLogix chassis, found in most ControlLogix systems installed in Vietnam between 2005 and 2015. Rockwell lists this catalog number as Discontinued since 31 December 2021 (lifecycle page on rockwellautomation.com, read 25 September 2026). Modules in service keep running; the problem is that when one fails there is no new genuine stock, and surplus stock is of unknown origin and carries no manufacturer warranty.

Replacing an Ethernet module is not simply a matter of pulling the old module and inserting a new one: the new module is a different catalog number in the Studio 5000 I/O tree, so the project has to be edited and downloaded again, and every device talking to this module (HMI, SCADA, other PLCs, drives) needs its connection checked.

The three current replacements — how they differ

Figures from 1756-TD003 (ControlLogix Communication Modules, EtherNet/IP connection table; edition 1756-TD003R, 01/2025, p. 4–6, 12–13, 41). The 1756-EN4TR supports PRP from firmware 4.001:

Read the table in this order of questions:

1. Is the existing network a star or a ring? Star network on ordinary switches → 1756-EN2T is sufficient and the cheapest. A DLR ring already in place or planned with POINT I/O, PowerFlex, Stratix → 1756-EN2TR (two ports, closes the ring itself).
2. How many connections is the ENBT carrying? The ENBT has only 128 CIP / 64 TCP; many systems run close to this limit without anyone having recorded it (SCADA, a historian, a few HMIs and PLC-to-PLC exchange are enough to reach it). The EN2T/EN2TR double this; the EN4TR has about four times the CIP connections and eight times the TCP connections. If the system has ever lost HMI connections when a client was added, go straight to the EN4TR.
3. Is system-level network redundancy (PRP) or 1 Gb speed required for a large SCADA/historian? → 1756-EN4TR. This is also the module that goes with ControlLogix 5580 (1756-L8xE) when ports are needed beyond the embedded port.

What to do when replacing — checklist

• Check firmware and Studio 5000 version on PCDC (compatibility.rockwellautomation.com): which firmware the new module needs, and whether the Studio 5000 version in use has a profile for that catalog number. The EN2T/EN2TR have profiles from older RSLogix 5000 versions; the EN4TR only has a profile in recent Studio 5000 versions — a system still running an old RSLogix 5000 may need the software upgraded as well; PCDC gives the exact minimum version.
• Back up the project (.ACD) and the old module's configuration (IP, subnet, gateway, produced/consumed connection table).
• In the project: replace the module in the I/O tree, keep the old IP address, reset electronic keying (Compatible Module), and review every produced/consumed tag and MSG instruction routed through this Ethernet path.
• Check every partner device: FactoryTalk View HMI, SCADA (AVEVA, Citect, WinCC), OPC server, neighbouring PLCs — their connections point to the IP and slot, not to the module catalog number, so most need no change; but each one must be tested after the swap.
• Replace on site in a short shutdown window: pull the old module, insert the new one (firmware and IP loaded beforehand in the workshop), download the project, check the LINK/NET LEDs, test communications.

When not to replace 1:1

• Systems with more than one ENBT in the same chassis to separate networks (separate SCADA, separate I/O): keep the architecture and replace each module with the corresponding EN2T/EN2TR — do not merge them into one EN4TR just because "it has more connections", as this also removes the network segmentation.
• The controller is also an older-generation 1756-L6x running RSLogix 5000: replacing the Ethernet module is only the first step; plan a migration of the controller as well to 5570/5580 (see 1756-L71, 1756-L83E) rather than investing piecemeal.