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Complete Guide

Modbus RTU Complete Guide

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

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

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.

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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Related Standards

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