Schneider Electric Implementation

Modbus RTU for Schneider Electric

Serial communication protocol using binary encoding over RS-232/RS-485. Most widely used industrial protocol worldwide.

Type: Serial CommunicationSpeed: Up to 115.2 kbpsReleased: 1979Organization: Modbus Organization

115.2 kbps max

Bandwidth

247

Max Nodes

1200m (RS-485)

Max Distance

Yes

Real-Time

Protocol Overview

Schneider Electric Modicon M340/M580 have native Modbus RTU through BMXNOM0200 serial modules. Unity Pro/Control Expert provides Serial Link Manager for easy configuration.

When to Use Modbus RTU

Choose Modbus RTU for simple applications, legacy integrations, cost-sensitive projects, or when connecting basic I/O devices over short to medium distances.

Schneider Electric Hardware Requirements

Compatible Communication Modules

BMXNOM0200 (M340/M580, 2x RS-232/485)

BMXP342020 (M340 CPU with built-in serial)

140NOM21x00 (Quantum, 2 ports)

BMXNOR0200 (M580 Remote I/O)

TM3SAC5R (TM3 for M221/M241/M251)

Wiring Details

BMXNOM0200 RS-485: Terminal 1 (D1+/A), 2 (D1-/B), 3 (GND). Max stub length 6m from trunk.

Termination

NO built-in termination. External 120Ω resistor across A-B at both physical ends required.

Schneider Electric Software & Programming

Function Blocks & Instructions

READ_VAR (Unity Pro)

WRITE_VAR (Unity Pro)

ADDM (Modicon legacy)

MSTR (M580)

MODBUS_Function_Block_Library

Schneider Electric Code Example

READ_VAR(
  EN := M10,
  ADDR := 1,  // Slave address
  OBJ_TYPE := 3,  // Holding registers
  OBJ_NUM := 1,  // Register 40001
  NB_OBJ := 10,
  DATA := %MW100:10,
  => ENO => M11,
  => GEST_STATUS => %MW50
);

Schneider Electric-Specific Implementation Notes

Serial Link Manager allows graphical configuration of Animation Tables for automatic cyclical polling. GEST_STATUS = 16#FDB1 (timeout), 16#FDB2 (illegal function). Schneider %MW0 = Modbus 400001 (1-indexed).

Technical Specifications

Physical Layer

Physical Layer: RS-232, RS-422, RS-485
Cable Type: RS-485 twisted pair, RS-232
Topology: Bus, Star, Tree
Power Over Cable: No

Data Layer

Data Link: Master/Slave
Encoding: Binary (RTU mode)
Error Detection: CRC-16
Frame Size: 256 bytes max

Performance

Scan Time: 10-100ms typical
Deterministic: Yes
Real-Time: Yes

Certification

Certification Required: No
License Cost: Free (open standard)
Version: Current

Advantages & Disadvantages

Advantages

✓Simple and easy to implement
✓Very low cost
✓Excellent industry support
✓Reliable in harsh environments
✓Minimal hardware requirements
✓Open standard
✓Wide device compatibility

Disadvantages

✗Limited speed (115.2 kbps max)
✗No built-in security
✗Master/slave only (no peer-to-peer)
✗Limited diagnostic capabilities
✗No standardized device profiles
✗Requires proper termination

Common Use Cases & Applications

Simple sensor and actuator networks

Building automation

Energy management systems

Water/wastewater treatment

Legacy equipment integration

Small to medium manufacturing lines

Industry Adoption

Adoption LevelVery High

Market Share30-40% of industrial protocols

Geographic PresenceWorldwide

Primary Industries

ManufacturingBuilding AutomationEnergyWater Treatment

Supported Message Types

Read Coils

Read Discrete Inputs

Read Holding Registers

Write Single Coil

Write Single Register

Write Multiple Registers

Supported PLC Brands

Siemens Allen-Bradley Mitsubishi Schneider Electric Beckhoff ABB Rockwell

Phoenix Contact

Wago

Protocol Comparisons

Modbus RTU vs PROFINET

Modbus RTU is simpler and cheaper; PROFINET is faster and more capable

View Detailed Comparison →

Quick Links

Alternative Protocols

Related Standards

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