ModbusViewer

A cross-platform (Windows + macOS) Modbus TCP/RTU master tool — a Qt6/QML clone of Modbus Poll, built with C++20 and CMake.

Screenshots coming soon.

Features

• Modbus TCP and RTU (serial) master, with a connection screen for both transport types (host/port for TCP; port/baud/data bits/parity/stop bits for RTU).
• Live polling of a contiguous register range (Normal view) or a hand-picked list of registers (Favorites view) — exactly one poll loop active at a time, retargeted live when you switch modes.
• Read coalescing: nearby targets are merged into the fewest possible read requests rather than one request per register.
• Register writes (function code 06) with immediate re-read to confirm.
• Value formatting per register: Signed/Unsigned Decimal, Hex, Binary, Float32, Int32 (Signed/Unsigned), with configurable byte order, scale, offset, and unit — editable per-row from a format picker.
• Addressing convention toggle: 0-based (PDU) or Modicon (4xxxx) style addresses, applied consistently across every address field.
• Tag database import from CSV or JSON, driving the Favorites picker and giving registers real labels/descriptions instead of bare addresses.
• Search/filter across label, description, address, and unit, live across both Normal and Favorites views.
• Communication log panel showing raw Tx/Rx frames and errors.
• Auto-reconnect with a "connection lost" state that keeps last-known values on screen (visually marked stale) rather than clearing them.
• Error/stale-value indication per cell when a poll target starts failing.

Requirements

• Qt 6.5 or newer (developed against 6.11.1)
• CMake 3.21+
• A C++20 compiler — developed with Qt's bundled MinGW 13.1.0 on Windows; any C++20-capable compiler with the required Qt modules should work
• Qt modules: Core Gui Qml Quick QuickControls2 QuickDialogs2 Network SerialPort Test

Building

cmake -S . -B build -DCMAKE_PREFIX_PATH="/path/to/Qt/6.11.1/<kit>" -DCMAKE_BUILD_TYPE=Debug
cmake --build build

On Windows with Qt's bundled MinGW kit:

$env:Path = "C:\Qt\Tools\mingw1310_64\bin;C:\Qt\Tools\Ninja;C:\Qt\6.11.1\mingw_64\bin;" + $env:Path
cmake -S . -B build -G Ninja -DCMAKE_PREFIX_PATH="C:/Qt/6.11.1/mingw_64" -DCMAKE_BUILD_TYPE=Debug
cmake --build build

The executable lands at build/ModbusViewer.exe (or build/ModbusViewer on macOS/Linux). To run it, only the Qt runtime libraries need to be on the loader path — not the full build toolchain.

Running the tests

cd build
ctest --output-on-failure

Tests are Qt Test-based and use a FakeTransport test double for protocol-layer coverage (no real socket/serial I/O needed), plus a real loopback QTcpServer for TCP connection-lifecycle coverage. RTU end-to-end coverage is similarly FakeTransport-based; the one thing that can't be faked is a real serial link, which this project has not yet been tested against.

Dev-time simulator

tools/pymodbus_simulator.py is a Modbus TCP/RTU slave simulator for exercising the app without real hardware, pinned to pymodbus==3.7.4 (see tools/requirements.txt).

pip install -r tools/requirements.txt
python tools/pymodbus_simulator.py --mode tcp --port 502

Project status

v1 milestones (M1 through M8 — protocol codec, TCP/RTU transports, polling engine with read coalescing and auto-reconnect, value formatting, tag database, Favorites, search, communication log, and packaging) are complete. See PROGRESS.md for exactly where things stand and docs/roadmap.md for what's planned post-v1. Architecture and design-decision rationale live in docs/, organized by topic (architecture.md, protocol.md, performance.md, favorites-search-tags.md, connection-ux.md, coding-standards.md).

Contributing

See CONTRIBUTING.md.

License

MIT — see LICENSE.