ProSoft MVI56-MCMR – Modbus Master/Slave Module for ControlLogix Redundant Systems

If you’re tying Modbus field devices into a Rockwell Automation ControlLogix platform—and you need controller redundancy—this module is purpose-built for that job. The ProSoft MVI56-MCMR is a ControlLogix in-chassis Modbus RTU/ASCII Master/Slave module designed to run in redundant 1756 controller architectures, letting you poll drives, meters, analyzers, PLCs, and RTUs without adding a separate gateway box. One thing I appreciate is how stable it tends to be in hot, busy networks; the deterministic backplane interface and well-documented data mapping keep commissioning time predictable.

Model clarification: You might notice it sometimes listed as “MVI156-MCMR.” The correct ProSoft model for the ControlLogix chassis is MVI56-MCMR.

Company’s Order Placement Process and Guarantees

• Warranty period: 365 days
• Delivery time: 1 week for in-stock; no more than 1 month at the latest
• Payment method: 50% advance payment; full payment prior to delivery
• Express options: FedEx, UPS, DHL

Key Features

• ControlLogix redundancy support – Designed for 1756 redundant controller systems, so failover events typically keep Modbus data available with minimal disruption.
• Dual serial ports (Modbus RTU/ASCII) – Two configurable RS-232/422/485 ports simplify mixed topology: multi-drop RS-485 to remote RTUs plus a local RS-232 service device in many cases.
• Master and Slave flexibility – Run as a Modbus Master to poll field instruments or as a Slave behind a DCS/SCADA; handy when projects evolve and roles change.
• Deterministic backplane data exchange – Tight integration with ControlLogix improves scan predictability; mapping tags through the module’s data blocks feels straightforward after the first setup.
• High throughput with configurable polling – Efficient request scheduling and block transfers help reduce network load, especially on large RTU strings.
• Industrial temperature rating – Suitable for common cabinet conditions; typically used in power, water/wastewater, and oil & gas sites.
• ProSoft Configuration Builder (PCB) – Configuration and diagnostics tools that make troubleshooting serial wiring and register maps less painful.

Technical Specifications

Real-World Use Cases

• Water treatment plant tying 40+ Modbus RTU instruments (analyzers and VFDs) into a redundant ControlLogix pair; the MVI56-MCMR handled polling on RS-485 multi-drops while maintaining stable handover during controller switchover.
• Power generation site using the module as a Modbus Slave to a legacy DCS, exposing ControlLogix process tags as Modbus registers without re-architecting the control network.
• Midstream oil facility polling remote tank gauging RTUs at mixed baud rates; staggered polls and careful termination typically kept bus collisions low.

From my experience, the biggest wins come from clean grounding, correct RS-485 biasing, and keeping similar device baud rates on a segment. It seems to be the difference between a smooth shift handover and nuisance timeouts when redundancy kicks in.

Related or Supporting Products

• ProSoft MVI56E-MCM – Enhanced Modbus RTU/ASCII module for ControlLogix; higher capacity and diagnostics, non-redundant by default.
• ProSoft MVI56-MCM – Standard (non-“R”) Modbus module for ControlLogix when redundancy is not required.
• ProSoft MVI69E-MCM – Modbus module for CompactLogix platforms if the project migrates away from 1756 chassis.
• ProSoft PLX31-MBTCP-MBS4 – Standalone Modbus TCP-to-RTU/ASCII gateway; practical when an in-chassis solution isn’t possible.
• Shielded RS-485 cabling and 120 Ω termination resistors – Recommended for long multi-drop segments to keep noise down.

Installation & Maintenance

• Cabinet & chassis – Install in a standard 1756 ControlLogix chassis with a suitable 1756 power supply. Allow front clearance for serial connectors and service access.
• Ventilation – Maintain airflow around the module; keep ambient within 0–60 °C. In most cases, a simple fan/filter is sufficient for dense cabinets.
• Wiring – Use shielded, twisted pair for RS-485; ground shield at one end only. Apply proper termination and biasing; keep drops short and avoid star topologies for RS-485.
• Port settings – Match baud, parity, and stop bits across each segment. A quick loopback test during commissioning can save a lot of time later.
• Safety & ESD – Power down the chassis when inserting/removing modules where procedures require; observe ESD practices to protect the backplane and serial transceivers.
• Routine maintenance – Periodically check diagnostic counters in PCB, verify that error/retry rates remain low, clean dust from the cabinet, and archive configuration files with firmware notes.
• Firmware & backups – Keep the module’s firmware and the controller’s AOI/sample ladder up to date; store backups offsite for redundancy changeovers.

Quality & Certifications

• CE and UL/cUL listed; RoHS compliant (typical for ProSoft MVI56 family).
• Designed for use in industrial control panels; meets common EMC/EMI requirements for process environments.
• Manufacturer warranty: typically 3 years (region and revision dependent); our coverage: 365 days as stated above.