ModbusScop Master is a free Modbus master / polling and testing tool with a modern, dockable Dear ImGui interface. It talks to real devices over Modbus TCP, Modbus UDP, and Modbus RTU (serial) — and can also send RTU-framed requests over TCP/UDP for terminal servers that bridge a network link to a serial RTU bus. It is built for engineers who need to poll, inspect, write, and troubleshoot many Modbus devices at once.
Free to use and redistribute under the permissive BSD 2-Clause License.
Developed by Carlos Nardi.
ModbusScop Master is organized as a tree: Channels → RTUs → Maps.
- A Channel is one connection. It is either a Network channel (TCP or UDP, with a per-channel framing choice — standard Modbus TCP (MBAP) or Modbus RTU (slave id + PDU + CRC, no MBAP)) or a Serial channel (a Modbus RTU bus on a COM port). Each channel runs on its own I/O thread; start and stop them independently.
- An RTU is one unit id behind a channel. A channel can host many RTUs, and because this is a master, several RTUs may even share the same unit id. Each RTU has an editable name and unit id.
- A Map is a poll definition under an RTU — the familiar poll window with its function code, address, quantity, and scan rate. Double-click a map to open its window. While a channel is Started, every map under it polls in the background at its own rate, so you can interface many devices simultaneously.
- Multi-device polling — many channels, each with many RTUs and maps, all polling concurrently. Network channels (MBAP framing) pipeline several requests in flight; serial and RTU-over-network channels are half-duplex, one transaction at a time.
- TCP, UDP, and Serial — connect over Modbus TCP, Modbus UDP, or Modbus RTU on a serial port, chosen per channel in the New Channel dialog (Network / Serial, and for Network TCP / UDP).
- Modbus RTU over the network — a per-channel framing selector lets a TCP or UDP channel carry RTU-style frames (slave id + PDU + CRC16, no MBAP header), the way terminal servers expose serial RTU devices over Ethernet.
- Dockable poll windows — one per map, each with its own function code, address, quantity, and scan rate; the unit id comes from the parent RTU. Arrange and dock them however you like.
- Rich data display — per-cell formats (Signed / Unsigned / Hex / Binary, plus 32- and 64-bit integers, floats, and doubles with selectable byte order), Base-1 register addressing, per-cell aliases, and a per-bit editor.
- New-value animation — poll cells flash when a freshly received value differs from the one they held. The tint, fade speed, and on/off are configurable under View → Animation Colors.
- Reading & writing — function codes 01–06, 15, 16, plus Mask Write Register (FC 22) and Read/Write Multiple Registers (FC 23). Write single cells straight from a read window with a double-click command popup.
- Tools — Inspect (send any single message and decode the reply, with a live FC 22 mask preview), Device Scan (sweep unit ids to find who's on the bus), and Register Scan (sweep an address range on one device). Point the tools at any channel from the channel's context menu or the Tools menu; results export to CSV.
- Diagnostics — a timestamped communication monitor with file logging and rotation, a human-readable status log, and a dashboard with live traffic counters and uptime.
- Workspaces — save and reload your entire setup: channels (including transport and framing), RTUs, every map, cell aliases, formats, and values. Individual maps can also be exported and imported on their own.
- Themes — dark / light / classic with a customizable accent color; layout and preferences are remembered between runs.
- Go to the Releases page and download the latest
ModbusScopMasterarchive for Windows. - Unzip it anywhere and run
ModbusScopMaster.exe— no installation required.
Requirements: Windows 10/11 (64-bit).
Rendering: ModbusScop Master uses the GPU by default; you can switch to CPU (software) rendering under View → Rendering (handy over Remote Desktop or in VMs).
- + Network or + Serial — create a channel.
- Network — choose TCP or UDP, the Framing (Modbus TCP (MBAP) or Modbus RTU over the network), the host/IP and port, and (for MBAP) the max parallel requests.
- Serial — pick the COM port and set baud rate, data bits, parity, and stop bits. Each new channel starts with one RTU (unit id 1); add more with Add RTU.
- + Map on an RTU — add a poll definition, then double-click it to open the poll window and set the function code, address, quantity, and scan rate.
- Press Start on the channel. Every map under it begins polling; watch the traffic in the Communication Monitor and the counters in the Dashboard.
Use File → Save Workspace (Ctrl+S) to keep the whole configuration and reload it later with Open Workspace (Ctrl+O).
ModbusScop Master is built with these open-source components, each under its own license:
| Library | Used for | License |
|---|---|---|
| Dear ImGui (docking) | user interface | MIT |
| GLFW 3 | window / OpenGL context | Zlib/libpng |
| OpenGL 3 | rendering | — |
| Asio (standalone) | Modbus TCP / UDP / RTU transport | Boost Software License 1.0 |
| stb_image | logo / splash decoding | MIT / public domain |
ModbusScop Master is released under the BSD 2-Clause License. It is provided "as is", without warranty of any kind; the author is not responsible for any damage or loss caused by its use.
BSD 2-Clause License
Copyright (c) 2026, Carlos Nardi
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modification, are permitted provided that the following conditions are met:
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