ModbusSim

Cross-platform Modbus simulation suite — includes ModbusSlave and ModbusMaster, built as Tauri 2 + Vue 3 desktop apps. Supports TCP, TCP+TLS, RTU, ASCII, and RTU-over-TCP transports.

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Download

→ Latest Release (v0.12.0)

Pre-built Tauri installers are attached to every GitHub Release:

Platform	Installer formats
macOS (Apple Silicon / Intel)	.dmg
Windows (x64)	.exe (NSIS) / .msi
Linux (x64)	.deb / .AppImage / .rpm

Note: As of v0.16, the native egui edition (assets with the -egui- suffix) is discontinued. Please migrate to the Tauri installers listed above.

Features

ModbusSlave — Slave Simulator

• Multi-Transport Support — TCP, TCP+TLS, RTU (serial), ASCII (serial), RTU-over-TCP
• Modbus TCP over TLS — TLS 1.2+ encryption, PEM and PKCS#12 certificate formats, optional mTLS (mutual authentication with client certificates)
• Multiple Slave Devices — Create connections on any port, add multiple slave devices per connection
• Four Register Types — Coils (FC01), Discrete Inputs (FC02), Holding Registers (FC03), Input Registers (FC04)
• Full Protocol Support — Read (FC01-04), Write Single (FC05/06), Write Multiple (FC15/16), with Modbus exception codes
• Register Table — Address search/filter, inline value editing, Ctrl/Shift multi-select, virtual scrolling (20,000+ registers), multi-format display (Auto / U16 / I16 / Hex / Bin / Float32 with 4 byte orders)
• Default Initialization — New slaves pre-fill addresses 0-20,000 across all four register types, batch-add supports up to 50,000 entries per operation
• Value Panel — Multi-format display: Signed/Unsigned/Hex/Binary (16-bit), Long/Float (32-bit), Double (64-bit), all byte orders (AB CD / CD AB / BA DC / DC BA)
• Dynamic Data Sources — Simulate changing register values: Fixed, Random, Sine wave, Sawtooth, Triangle, Counter, CSV playback
• Communication Log — Real-time TX/RX logging with search, direction/function-code filtering, and CSV export
• Project Files — Save/load complete configurations as .modbusproj files for quick scenario switching
• Serial Port Support — Auto-detect system serial ports, configurable baud rate, data bits, stop bits, parity

ModbusMaster — Master Tool

• Multi-Transport Support — TCP, TCP+TLS, RTU (serial), ASCII (serial), RTU-over-TCP
• Modbus TCP over TLS — TLS 1.2+ encryption, PEM and PKCS#12 certificate formats, accept-invalid-certs mode for self-signed certificate testing
• Scan Groups — Configure periodic polling with custom intervals per register group, per-group slave ID override
• Device Discovery — Slave ID scan (1-247), register address scan, auto-add discovered devices to scan groups
• Multi-format Data View — Unsigned, Signed, Hex, Binary, Float32 (AB CD / CD AB), virtual scrolling
• Write Operations — Write single/multiple coils and registers (FC05/06/15/16)
• Communication Log — TX/RX logging with search/filter (direction, function code, text)
• Auto-Reconnect — Configurable reconnection with exponential backoff (1s → 2s → 4s → ... → 30s max)
• Project Files — Save/load connection and scan group configurations
• Connection-on-Scan — Auto-prompt to scan devices after successful connection

Shared Architecture

• Unified Error System — Structured ModbusError with categorized error types (connection/protocol/application), serialized to JSON for frontend parsing
• Shared Vue Components — Common composables and types shared between both Tauri apps via the shared-frontend npm workspace

Supported Function Codes

Code	Function	Slave (Server)	Master (Client)
FC01	Read Coils	Read	Read/Poll
FC02	Read Discrete Inputs	Read	Read/Poll
FC03	Read Holding Registers	Read	Read/Poll
FC04	Read Input Registers	Read	Read/Poll
FC05	Write Single Coil	Write	Write
FC06	Write Single Register	Write	Write
FC15	Write Multiple Coils	Write	Write
FC16	Write Multiple Registers	Write	Write

Transport Modes

Mode	Transport	Framing	Use Case
TCP	TCP/IP socket	MBAP header	Standard Modbus TCP
TCP+TLS	TLS over TCP	MBAP header	Secure Modbus TCP (TLS 1.2+)
RTU	Serial port	Slave ID + CRC-16	RS-485/RS-232 devices
ASCII	Serial port	: + hex + LRC + CRLF	Legacy serial devices
RTU-over-TCP	TCP/IP socket	Slave ID + CRC-16	Industrial gateways

Tech Stack

• Core (Rust): tokio-modbus + tokio-serial
• TLS: native-tls (system TLS: macOS Security.framework, Linux OpenSSL, Windows SChannel)
• Tauri UI: Vue 3 + TypeScript + @tanstack/vue-virtual on Tauri 2
• Serial: serialport for port enumeration

Project Structure

ModbusSim/
├── crates/
│   ├── modbussim-core/        # Core library: protocol, transport, registers, logging
│   │   ├── src/
│   │   │   ├── slave.rs       # Slave connection (TCP/RTU/ASCII/RtuOverTcp dispatch)
│   │   │   ├── master.rs      # Master connection with multi-transport support
│   │   │   ├── frame.rs       # RTU/ASCII frame encode/decode
│   │   │   ├── pdu.rs         # Modbus PDU request/response parsing
│   │   │   ├── transport.rs   # Transport enum, serial config, TLS config, port enumeration
│   │   │   ├── mbap.rs        # MBAP frame encoding/decoding (for TLS mode)
│   │   │   ├── tls_slave.rs   # TLS-enabled Modbus TCP slave server
│   │   │   ├── tls_master.rs  # TLS-enabled Modbus TCP master client
│   │   │   ├── register.rs    # Register types, encoding/decoding
│   │   │   ├── data_source.rs # Dynamic data sources for register simulation
│   │   │   ├── reconnect.rs   # Reconnect policy with exponential backoff
│   │   │   ├── error.rs       # Unified ModbusError enum
│   │   │   ├── project.rs     # .modbusproj file save/load/migrate
│   │   │   ├── log_collector.rs # Thread-safe log ring buffer
│   │   │   └── ...
│   ├── modbussim-app/         # Tauri app — ModbusSlave
│   └── modbusmaster-app/      # Tauri app — ModbusMaster
├── shared-frontend/           # Shared Vue composables and components (Tauri UI)
│   └── src/
│       ├── composables/       # useDialog, useValueFormat, useLogPanel, useLogFilter, useErrorHandler
│       ├── components/        # AppDialog
│       └── types/             # Shared TypeScript types
├── frontend/                  # Vue 3 frontend — ModbusSlave
└── master-frontend/           # Vue 3 frontend — ModbusMaster

Development

Prerequisites

• Rust (stable)
• Node.js (v18+)
• Tauri CLI

Setup — Tauri edition

# Install frontend dependencies (npm workspaces)
npm install

# ModbusSlave (dev mode)
cd crates/modbussim-app && cargo tauri dev

# ModbusMaster (dev mode)
cd crates/modbusmaster-app && cargo tauri dev

Build — Tauri edition

cd crates/modbussim-app && cargo tauri build
cd crates/modbusmaster-app && cargo tauri build

Run Tests

cargo test --workspace

Changelog

See CHANGELOG.md for the full version history, or browse the Releases page for downloadable binaries.

License

MIT

Author

kelsoprotein-lab