ModbusKit Online Tools

ModbusKit Help

Find the right tool, understand common Modbus settings, and troubleshoot unexpected results.

Where to start

Choose a tool, look up an answer or contact us.

FAQ

Common questions

Answers about addresses, byte order and connection issues.

Sitemap

Page directory

Find tool pages, guides and website information.

Modbus RTU

Browser tool

Generate a frame or inspect a received message.

Contact

Email support

Send a question, bug report or feature request.

Topics to explore

Use these topics to guide your next steps. Tool pages include instructions, and the FAQ covers common questions.

Getting started

4 topics

Understand the settings before building a frame.

Choose a protocolCheck whether your device uses RTU, ASCII or TCP.
Build a read requestChoose a function, device address, start address and quantity.
Select a function codeMatch the operation to the device register map.
Check address notationDistinguish protocol offsets from labels such as 40001.

Using the tools

4 topics

Generate frames, check messages and decode values.

RTU frame generationCreate a request with a calculated CRC.
Frame parsingPaste a complete frame and inspect its fields.
Serial debuggingConnect an authorized device in a browser with Web Serial support.
CRC checksCalculate or verify CRC in the RTU tool.

Troubleshooting

4 topics

Check the cause before changing device settings.

No serial connectionCheck browser support, port permissions, drivers and other open applications.
CRC mismatchCheck frame boundaries, missing bytes and serial settings.
Unexpected valuesCheck the data type, byte order, register address and scale.
Intermittent responsesCheck wiring, bus timing and device response time.

Working with devices

4 topics

Use the device manual to confirm protocol and data details.

Polling multiple devicesUse unique addresses and wait for each response or timeout.
Floating-point registersCompare IEEE 754 values across the supported byte orders.
Vendor-specific functionsCheck the device specification; generated requests cover the listed functions.
Safe device accessConfirm the device and register before sending a write request.

A practical sequence

Start with a known frame, understand its fields, then test with an authorized device.

1

Learn the frame

Identify the protocol, function and address.

RTU, ASCII and TCP
Function codes
Address notation
2

Check the data

Build and parse a message without connecting a device.

Request generation
Frame parsing
Value conversion
3

Connect a device

Match serial settings and test a documented read request.

Port permission
Serial settings
Response checks
4

Investigate results

Compare responses with the device register map.

Byte order
Polling intervals
Write precautions

Still need help?

Send the tool name, your browser and a small example that reproduces the issue.

Contact support[email protected]
RepliesTiming depends on the request.
Useful detailsSteps, expected result and actual result

More examples

The blog contains tool guides and protocol examples.