Allen-Bradley SST-ESR2-CLX-RLL ControlLogix Modbus TCP & Serial Module

Description

Product Introduction

The Molex SST-ESR2-CLX-RLL is an in-chassis communication module designed to integrate Modbus network protocols directly into the Allen-Bradley 1756 ControlLogix backplane. Functioning as an independent protocol gateway, it houses one 10/100 Fast Ethernet port and two galvanically isolated serial channels. This allows a ControlLogix processor to simultaneously manage Modbus TCP (Client/Server) and Modbus Serial (Master/Slave in RTU or ASCII) traffic without needing external protocol converters or third-party gateways.

Engineered for seamless integration, the module comes provided with Add-On Profiles (AOP) for RSLogix 5000 / Studio 5000 environment setup. The “RLL” (Remote Link Library) feature enables maintenance teams to remotely configure, monitor, and run diagnostic checks on connected Modbus field networks through existing Rockwell network passes (EtherNet/IP, ControlNet, or DeviceNet) using the SST Windows Console software.

Key Technical Specifications

Application Scenarios & The “Trench” Experience

A gas turbine skid monitored by a ControlLogix L71 controller drops communication with its field power meters and valve actuators because an external standalone serial-to-Ethernet gateway overheats inside the junction box. The PLC loses real-time flow and power diagnostics, triggering a conservative safety trip. Replacing external wall-mounted gateways with an in-chassis SST-ESR2-CLX-RLL module eliminates external power supplies, reduces cabinet wiring points, and pulls Modbus power data straight across the 1756 backplane into controller tags at backplane speeds.

• Power Generation & Substation Metering: Polling Modbus RTU electrical meters, protective relays, and UPS systems over RS-485 while serving Modbus TCP data to plant SCADA.
• HVAC & Building Automation Interface: Interfaces ControlLogix with Variable Frequency Drives (VFDs) and chillers using native Modbus RTU/TCP protocols.
• Oil & Gas Flow Measurement: Reads multi-drop gas flow computers and tank gauging systems over long-distance RS-482/485 serial runs.
• Water/Wastewater Treatment Plants: Collects field data from chemical dosing pumps and water quality transmitters running on Modbus serial connections.

SST-ESR2-CLX-RLL

SST-ESR2-CLX-RLL

Transparency SOP: Quality Assurance & Testing

1. Visual & Hardware Inspection: Visual check of the 1756 backplane connector pins, RJ45 port latches, USB port, and faceplate PCB housing.
2. Backplane & Power Verification: Inserted into a live 1756-A7 chassis to verify proper 5V/24V power draw, boot sequence, and initialization on the 4-character scrolling LED display.
3. Firmware & USB Port Audit: USB port connectivity is verified for configuration backup, restoration, and firmware flash integrity using the SST Console.
4. Active Communications Loop Testing:
   • Ethernet: Modbus TCP Client/Server ping and data polling loopbacks against test slave simulators.
   • Serial: RS-232 and RS-485 loopback tests across both serial channels at 115.2 Kbps to verify signal isolation and frame delivery.
5. Final Cleaning & Packaging: Cleaned, packed in anti-static ESD bags, and enclosed in custom-cut foam shipping boxes.

The Veteran’s Tech Trap Guide (Crucial Value-Add)

• ⚠️ RJ45 Serial Pinouts differ from Standard Ethernet: The two serial ports on the front faceplate use RJ45 connectors (not DB9). Connecting a standard Ethernet patch cable from these serial ports into an Ethernet switch will short serial signals and disable the port. Use the provided Molex RJ45-to-DB9 male adapter cables for serial connections.
• ❗ Direct I/O vs. Messaging Memory Limits: When mapping Modbus registers, ensure your cyclic data fits within the 496-byte input / 496-byte output direct I/O limit for fastest performance. If your system exceeds 496 bytes, you must use CIP Explicit Messaging via MSG instructions to read/write to the module’s 32K word shared memory.
• ⚠️ RLL Remote Link Driver Setup: To use RLL (Remote Link Library) for remote configuration over EtherNet/IP, ensure RSLinx is properly configured with CIP pass-through enabled. Firewall blockages on port 7000/7001 can disrupt SST Configuration Console linkup.
• ❗ Serial Termination Resistors: When operating Port 1 or Port 2 in RS-485 2-wire mode, internal software termination can be enabled via the console, or physical 120-ohm resistors must be placed across Rx/Tx terminals at line ends to avoid signal reflection issues on long runs.

Frequently Asked Questions (FAQ)

Q: What is the difference between SST-ESR2-CLX-RLL and ProSoft MVI56E-MNET?

A: Both modules bridge Modbus to ControlLogix. The SST-ESR2-CLX-RLL offers both Ethernet Modbus TCP and 2x Serial Modbus ports in a single slot, whereas ProSoft typically offers separate modules for MNET (Ethernet) and MCM (Serial).

Q: Do I need to write complex Ladder Logic to configure the SST module?

A: No. Modbus device configurations, baud rates, and register mapping are built using the Windows-based SST Configuration Console. Data is mapped directly into ControlLogix controller tags via the Add-On Profile (AOP).

Q: Can this module act as a Modbus TCP Client and Server at the same time?

A: Yes. The Ethernet channel supports simultaneous Master (Client) requests to field devices while serving data to an upper-level SCADA system as a Slave (Server).

Q: Is the SST-ESR2-CLX-RLL compatible with Studio 5000?

A: Yes. It supports RSLogix 5000 and Studio 5000 using the Molex/SST Add-On Profile (AOP) for direct module property setup.

Q: What warranty is supplied on surplus or reconditioned modules?

A: All New Surplus and fully reconditioned modules include a full 12-month replacement warranty from the invoice date.