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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

SiemensAllen-BradleyMitsubishiSchneider ElectricBeckhoffABBRockwell
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

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