Mitsubishi Electric Implementation

Modbus RTU for Mitsubishi 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

Mitsubishi FX5U/Q-series have excellent native Modbus RTU support via function blocks in GX Works3. FX5-485-BD board provides RS-485 interface with software-configurable parameters.

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.

Mitsubishi Electric Hardware Requirements

Compatible Communication Modules

FX5-232-BD (RS-232, up to 115200 baud)

FX5-485-BD (RS-422/485 multi-point)

QJ71C24N (Q-series, 2x RS-232C)

QJ71C24N-R2 (Q-series, 2x RS-422/485)

FX3U-485ADP-MB (FX3U adapter)

Wiring Details

FX5-485-BD: Terminal SDA (Data+), SDB (Data-), SG (Signal Ground). Shielded twisted pair 0.75-1.25mm².

Termination

Built-in switchable 120Ω termination. SW1=ON enables termination, OFF disables. Enable only at bus ends.

Mitsubishi Electric Software & Programming

Function Blocks & Instructions

MODBUS_Master (FX5/Q series)

MODBUS_Slave (FX5/Q series)

MODRW (FX3 series)

FX5_MODBUS_COM

MODBUSRTU_MASTER

Mitsubishi Electric Code Example

MODBUS_Master(
  Enable := M101,
  Port := 0,
  Command := 3,  // FC03 Read Holding
  Station := 1,
  StartAddr := 0,  // 0-indexed
  NumRegs := 10,
  DataAddr := D100,
  Timeout := 1000,
  => Done := M102,
  => Error := M103,
  => ErrCode := D50
);

Mitsubishi Electric-Specific Implementation Notes

0-indexed addressing (Modbus 40001 = D0). GX Works3 has dedicated Modbus configurator GUI. Error code 1004H = no response, 1001H = illegal function. FX5U can handle 4 simultaneous requests per port.

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

Adoption & Ecosystem Context

Adoption LevelVery High

Primary-source 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

IEC 61131-3
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