Modbus Simulator

A lightweight Modbus TCP simulator designed for testing, development, and integration of Modbus-based systems.

The simulator provides:

• Multiple Modbus TCP server instances
• Configurable register generators
• Optional HTTP API for runtime interaction
• CLI and YAML-based configuration

Avaliable as docker image for amd64 and arm64: https://hub.docker.com/r/mrhlebusheck/modbus_simulator

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Build

Dependencies

Debian (13+)

sudo apt update
sudo apt install -y \
  make \
  pkg-config \
  gcc \
  libmodbus-dev \
  libyaml-dev

Arch Linux

sudo pacman -S --needed \
  base-devel \
  pkgconf \
  libmodbus \
  libyaml

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Compile

Debug build

make

Release build

make NDEBUG=1

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Overview

The simulator can be started in two ways:

• Using a YAML configuration file
• Using command-line arguments (limited mode)

Configuration File

./build/modbus_simulator -c config.yaml

Provides full functionality, including:

• Multiple simulators
• Generators
• Web API configuration

CLI Mode

./build/modbus_simulator --web 0.0.0.0:8080 --modbus tcp:0.0.0.0:502

Limitations:

• No generator configuration
• Only Modbus TCP supported

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Features

• Multiple independent Modbus TCP servers

• Register types:

  • Coil
  • Discrete Input
  • Input Register
  • Holding Register

• Data generators:

  • random_walk
  • sequence_walk

• HTTP API:

  • Read/write registers
  • Control simulator lifecycle (start/stop)

• Debug/verbose mode (global and per-component)

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Documentation

• usage.md — CLI usage and modes
• config-yaml.md — YAML configuration reference
• api.md — HTTP API specification

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Notes

• Register values are stored as 16-bit units internally.
• 32-bit types and floats are mapped to two consecutive registers.
• Designed primarily for development and testing.