PLC & RTU testing
Check coils and registers, confirm function-code support, test writes and see the raw request and response frames.
Windows 10 / 11New: v2.1.0
ModbusBB 2.0 — Modbus master & simulator for Windows
Test several devices at once over Modbus TCP, RTU, ASCII, RTU-over-TCP and UDP, see the exact TX/RX bytes, run FC08/17/22/23/43 diagnostics and script it all from the CLI.
✓ 30-day trial✓ No credit card✓ $10 lifetime license✓ 1.x keys keep working
- TCP · RTU · ASCII · UDP+ RTU over TCP
- Master + SimulatorGUI and CLI
- Raw TX/RX framesHex traffic monitor
5 transportsTCP, RTU, ASCII, RTU-over-TCP, UDP
11 data types16/32/64-bit, float, string
Raw TX/RXHex traffic monitor
GUI + CLIJSON, CSV and exit codes
Built for field work
From first connection to final troubleshooting
Use ModbusBB for commissioning, FAT/SAT, integration testing, register-map checks, fault finding and quick bench simulation.
SCADA integration
Check device maps and data types before integrating points, then simulate field values, delays and exceptions when hardware isn't available.
Meters & analyzers
Start from a built-in register map, then decode 16/32/64-bit values with scaling, units and the right byte order.
Drives & inverters
Read operating values, identify the device with FC43, investigate timeouts and log values during commissioning.
Latest release: 2.1.0
What's new in ModbusBB 2.0
The biggest update since launch. It's a free update for every license holder, and your existing key keeps working.
Multiple connections
Connect to several devices or networks at once. Each connection has its own poll tabs, and all of them can run at the same time.
Connections →Workspaces (.mbws)
Save connections, polls, register settings and watchdog rules in one file. Your 1.x connection profiles and .mbcfg files open directly.
Workspaces →RTU-over-TCP and UDP
Added alongside TCP, RTU and ASCII. Retries and automatic reconnect with back-off keep long tests running.
Transports compared →Traffic monitor
Every TX/RX frame in hex, with a filter by text, direction or connection. Pause, copy, or export to CSV/TXT.
Traffic monitor →64-bit and string values
Float64, Int64, UInt64 and String join the 16/32-bit types, all in four byte orders. Adds scale/offset/unit and Modicon addressing.
Byte order guide →Device Tools
Device Identification (FC43/14), Report Slave ID (FC17), Diagnostics (FC08), Mask Write (FC22), Read/Write Multiple (FC23), plus a raw request sender.
Device Tools →Device library
Nine register maps for Eastron, Schneider, Carlo Gavazzi, SunSpec, Growatt, SMA and ABB devices. Each lists its source; always verify it against your device manual.
Device library →Simulator upgrade
TCP/UDP/RTU/ASCII, several unit IDs, value generators (ramp, sine, random, counter, toggle), exception injection and response delay.
Simulator guide →Trend, watchdog and CLI
Zoomable trend chart with CSV/PNG export. Alert rules can log, play a sound or write a register. The one-shot CLI outputs JSON, CSV or NDJSON.
CLI reference →
Core workflow
DECODE
DIAGNOSE
SIMULATE
AUTOMATE
Everything you need to see what the device is actually doing
More than a register grid. ModbusBB combines connectivity, decoding, diagnostics, simulation and evidence capture.
CONNECT
Five transports, many connections
Ethernet or serial: IP/port, COM port, baud, parity, data bits, stop bits, timeout and retries. Auto-reconnect with back-off recovers dropped links, and response times show in the log.
TCP 192.168.1.100:502
RTU COM3 · 9600 · 8E1
R/TCP 10.0.0.5:4001
RTU COM3 · 9600 · 8E1
R/TCP 10.0.0.5:4001
Data types & byte order
Binary, Hex, 16-bit, Int32/UInt32/Float32, Int64/UInt64/Float64 and String, in ABCD, DCBA, BADC or CDAB order, with scale, offset and unit.
Learn byte order →Traffic, scans & device tools
See raw frames, find responding unit IDs and register ranges, and send FC08/17/22/23/43 or any raw request.
Fix timeouts →Built-in device simulator
Run ModbusBB as a slave/server with generated values, several unit IDs and injected exceptions for testing masters.
Simulator guide →Trends, alerts, CSV & CLI
Trend live values, raise alerts on engineering values, log to CSV and run the same checks from scripts.
Modbus command line →Quick answer
What is ModbusBB?
ModbusBB is Windows software for engineers and technicians who need to talk to, diagnose or simulate Modbus devices. It is a Modbus master/client for reading and writing field devices, and also a Modbus slave/server simulator. Version 2.0 supports Modbus TCP, RTU, ASCII, RTU-over-TCP and UDP. It can run several connections at once and shows the raw TX/RX frames. It also adds device diagnostics (FC08, 17, 22, 23 and 43), a register-map library, trends, watchdog alerts, CSV logging and a scriptable CLI.
Use it with PLCs, gateways, meters, drives, inverters, remote I/O and SCADA-connected equipment that has a Modbus interface.
Learn & troubleshoot
Technical guides engineers actually search for
Short, practical references built around common commissioning problems, not generic protocol summaries.
Addressing
40001 vs address 0
Understand 0-based, 1-based and Modicon notation and avoid off-by-one register errors.
RS-485Wiring & termination
Check A/B polarity, daisy chains, biasing, shields and end termination.
ProtocolFunction codes explained
FC 01–06, 15, 16 plus diagnostics, mask write, read/write multiple and device identification.
TroubleshootingFix Modbus timeouts
A step-by-step TCP and RTU checklist using the raw traffic monitor.
DataFloat32, 64-bit & byte order
Decode ABCD, DCBA, BADC and CDAB for 32- and 64-bit values and strings.
AutomationModbus command-line tool
Script reads, writes and polls with JSON/CSV output and exit codes.
Simple licensing
FREE TRIAL
LIFETIME
Try the complete tool before buying it
The trial has every feature, limited to 15-minute sessions. The paid license is a one-time purchase.
$0
- 30-day evaluation
- 15 minutes per session
- All product features
- No credit card
$10
1 user · up to 3 computers
- Unlimited session time
- 3 device activations
- Works offline up to 30 days between checks
- Free updates, including 2.0
ModbusBB FAQ: 2.0, pricing, licensing and requirements
Can ModbusBB connect to several devices at the same time?
Yes. Since version 2.0 you can add as many connections as you need, for example a TCP PLC, an RTU meter bus and a UDP device. Each connection has its own poll tabs, and all polls can run at the same time. Save the setup as a workspace (.mbws) to reopen it later.
Which Modbus transports does ModbusBB 2.0 support?
Modbus TCP, Modbus RTU, Modbus ASCII, RTU-over-TCP (RTU frames over a TCP socket, as used by serial device servers) and Modbus UDP. Serial connections support 1200 to 230400 baud, 7 or 8 data bits, parity None/Odd/Even/Mark/Space and 1, 1.5 or 2 stop bits.
Does my existing license key work with version 2.0?
Yes. Existing ModbusBB keys keep working with 2.0 at no extra cost. Install 2.0 over your current version. ModbusBB finds your stored key when it starts and re-activates it for that PC. That step needs an internet connection once.
How do I upgrade from ModbusBB 1.x to 2.0?
Download the 2.0 installer and run it over your current installation. Don't uninstall first, because uninstalling removes the stored key and settings. If you already uninstalled, enter the key from your purchase email again. The first start re-activates the key online. Old connection profiles (.json) and .mbcfg files open through File > Open Workspace.
How much does ModbusBB cost?
A ModbusBB license is a one-time payment of $10 (USD) for a lifetime license with free updates, including 2.0. There is no subscription. You can try every feature first with the free 30-day trial.
What are the limits of the free trial?
The trial runs for 30 days with all features enabled. Each session is limited to 15 minutes. No credit card is required to download it.
How many computers can I use one license on?
One license can be active on up to 3 devices at the same time. To move it to a new PC, deactivate an old device in the self-service license portal and activate the new one.
Which operating systems does ModbusBB support?
ModbusBB runs on 64-bit Windows 10 and Windows 11. The .NET 8 runtime is built into the application, so there is nothing else to install. An installer and a portable ZIP are both available.
Which Modbus function codes are supported?
Reads and writes use FC 01, 02, 03, 04, 05, 06, 15 and 16. Device Tools and the CLI add FC 08 (Diagnostics), FC 17 (Report Slave ID), FC 22 (Mask Write Register), FC 23 (Read/Write Multiple Registers) and FC 43/14 (Read Device Identification). The raw request sender can send any function code from 1 to 127.
Does ModbusBB work offline?
Yes. After activation, ModbusBB works offline for up to 30 days between online license checks. It talks to your devices directly over your network or serial port. No register values or logs are sent to our servers.
Ready to test a device?
Download ModbusBB 2.0 and connect in minutes
Installer and portable versions are available for Windows 10/11 (64-bit).