Product Description of ProSoft MVI71-MCM

MVI71-MCM (Modbus Master/Slave Communication Module) is a dual-port Modbus master/slave communication module specially developed by ProSoft for the Rockwell PLC-5 platform. It provides 2 fully isolated serial ports (RS-232/422/485) and supports both Modbus RTU/ASCII protocols, enabling stable data interconnection between PLC-5 and a wide range of Modbus devices such as frequency converters, instruments, sensors, and third-party PLCs. It is a standard solution for industrial automation system integration. 

I. Model Analysis

MVI71: Special Series for PLC-5 1771 Platform

MCM: Modbus Master/Slave (Modbus Master / Slave)

Core Positioning: Modbus RTU/ASCII, Master + Slave dual mode, 2 independent fully isolated serial ports, RS-232/422/485, single slot, zero PLC load, 6000-word database

II. Core Hardware Specifications

Compatible Platforms

PLC-5: Full series PLC-5/11, /12, /15, /20, /25, /30, /40, /40L, /60, /80, /80E

1771 Backplane, single-slot installation

Support for local / remote racks

Backplane power consumption: Maximum 800mA @ 5.1VDC

Serial Interfaces

Configuration Port (CFG/P1): 1 path RJ45 (RS-232), used for module configuration, debugging, firmware upgrade

Application Port (P2, P3): 2 independent, jumper selectable RS-232 / RS-422 / RS-485, RJ45 (with DB9 adapter)

RS-232: Point-to-point (15m)

RS-422: Full-duplex long-distance (1200m)

RS-485: Half-duplex multi-point (32 nodes, 1200m)

Electrical Isolation: 500Vrms optical isolation (between the backplane and all serial ports)

Baud Rate: 110 ~ 115200 bps

Data Format: 8/N/1, 8/E/1, 8/O/1

Protocol Support

Modbus: Master (Master) + Slave (Slave) dual mode

Modbus RTU: Binary, high-speed (default)

Modbus ASCII: Character type, compatible with old equipment

Function Codes: Support all standard Modbus function codes (01, 02, 03, 04, 05, 06, 08, 15, 16)

Data Buffer: 6000 words Bidirectional Shared Database

Master Station Function

Each port can poll up to 32 Modbus slave stations

Support for continuous / single-shot / event-triggered polling

Each port can be independently configured and have an independent polling list

Slave Station Function

Respond to Modbus master station read/write requests

Map data to PLC-5 file registers

LED Status: OK, BP, P2, P3, ERR five groups of indicator lights Work environment

Temperature: 0°C ~ +60°C

Storage: -40°C ~ +85°C

Humidity: 5% ~ 95% (no condensation)

Shock resistance: 30g (during operation), 50g (when not in operation)

Certifications: CE, UL/cUL, RoHS, DNV

III. Core Functions and Performance

1. Dual-mode Modbus Master/Slave (Core Advantage)

Master mode (Master)

Active polling: PLC-5 acts as the master station, reading/writing data from remote Modbus slave stations

32 slave stations / ports: A single module can connect up to 64 Modbus devices (2 ports × 32)

Dual protocol parallel: P2 = RTU, P3 = ASCII, connecting devices of different protocols simultaneously

Polling optimization: Supports data change reporting, dead zone control, batch reading, reducing network load

Error handling: Automatic retry, timeout, slave station fault isolation

Slave mode (Slave)

System access: PLC-5 acts as a slave station, connecting to SCADA systems, DCS, or third-party Modbus master stations

Data security: Configurable read/write permissions, address range, data block protection

High-speed response: Independent processor, zero PLC load, response time < 10ms

Full compatibility of Modbus RTU/ASCII

RTU: Industrial standard, high speed, efficient, short frames

ASCII: Compatible with old instruments, sensors, character devices

Automatic verification: CRC (RTU), LRC (ASCII), ensuring data integrity

2. Two fully isolated serial ports (High reliability)

Dual ports are completely independent

P2/P3 do not interfere with each other, independent protocols, parameters, polling lists

Dual networks parallel: Connect two independent Modbus buses simultaneously

RS-232/422/485 three modes

Compatible with point-to-point, long-distance, multi-point bus all topologies

500V full isolation: Anti-surge, anti-static, eliminating ground circulating current

Multi-point network

RS-485 supports 32 nodes, saving wiring and reducing costs

3. Deep integration with PLC-5 system

PLC memory mapping

6000-byte shared database: Direct mapping of PLC-5 files (N, B, F, T, C)

BTR/BTW block transmission: Efficient data interaction, zero PLC programming

Module status, port status, slave station status, errors all mapped to PLC tags

Configuration tool

ProSoft Configuration Builder (PCB): Visual configuration

Modbus parameters, polling lists, mapping rules graphical editing

Online diagnosis: Real-time monitoring, message capture, event logs, error statistics

4. Industrial-grade reliability

Full electrical isolation

300Vrms triple isolation: Port - Port, Port - Backplane, Port - Power supply

Stable operation in industrial environments, strong interference, ground potential difference, lightning strikes

Independent operation

Zero PLC CPU load,不影响 scanning cycle

Module failure does not affect PLC host

Powerful diagnosis

Link status， slave station status， communication quality， error count real-time monitoring

Automatic reconnection in case of disconnection， command retry， fault isolation

Detailed event logs， error codes， quick troubleshooting

IV. Core Features and Advantages

1. Professional Modbus communication

Dual-mode Modbus Master/Slave： Fully compatible in all scenarios

Modbus RTU/ASCII： Compatible with all Modbus devices

2. Two independent isolated serial ports： Dual network parallel， saving slots 500V fully isolated: industrial-grade protection

6000-word database: capable of handling large-scale data interaction

2. Optimized for PLC-5

1771 single slot: compatible with all PLC-5

BTR/BTW efficient transmission: native data interaction of PLC-5

Zero PLC load: does not affect the performance of the control system

3-year warranty, global technical support

3. Flexible, universal, easy to use

RS-232/422/485 three modes: fully compatible with all topologies

32 slave stations / ports: large capacity, high scalability

PCB visual configuration: quick deployment, no low-level programming required

Sample program + ladder diagram: ready to use, shortens the development cycle

Wide temperature range, shock-resistant, no fan: long-term stability, maintenance-free

4. Industry standard certification

Global certification: UL/cUL, CE, RoHS, DNV

Preferred for industrial automation: power, metallurgy, chemical industry, water treatment, food, mining

5. Typical application scenarios

PLC-5 polling Modbus devices: frequency converters, instruments, sensors, valves, meters

PLC-5 accessing SCADA/DCS: as a Modbus slave station, accessing the upper system

Multi-PLC interconnection: PLC-5 ↔ Modicon, Siemens, Mitsubishi and other third-party PLCs

Renovation of old factories: upgrading the old PLC-5 system to a Modbus network to protect investment

Distributed I/O: connecting remote Modbus I/O modules to expand I/O points

Data collection: centralized collection of Modbus devices in production lines, pumping stations, substations, and pipelines

6. Summary

MVI71-MCM is the flagship solution for Modbus communication on the PLC-5 platform. With Modbus master/slave dual mode, RTU/ASCII dual protocols, 2 independent fully isolated serial ports (RS-232/422/485), 6000-word large-capacity database, zero PLC load, industrial-grade full isolation, deep integration of PLC-5, global certification as core advantages, it is specifically designed for industrial automation, system integration, device networking, and factory renovation. It is a high-performance, highly reliable, one-stop standard module for Rockwell PLC-5 accessing the Modbus industrial network.