Modbus RTU Serial Debugger
Connect a serial device in a browser with Web Serial support. Send requests, inspect responses and chart parsed values.
Serial Settings
Baud Rate
Data Bits
Stop Bits
Parity
Serial access is unavailable in this browser. Open this page in a supported desktop browser such as Chrome or Edge.
Serial Log
Record Limit
Display Format
Modbus Mode
Input Format
Device Address (HEX)
Function Code (HEX)
Start Address (HEX)
Quantity (HEX)
ms
RTU Response Parser
Data Source
Data Format
Enable Parsing
| Index | Rule Name | Byte Offset | Data Type | Byte Order | Coefficient | Constant | Decimal Places | Actions |
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Raw Messages
Record Limit
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How to Use the Serial Debugger
Serial and RTU troubleshooting
Connect and Inspect RTU Data
Connect to a serial device, send requests and inspect RTU read responses. Serial access requires a supported desktop browser and permission to use the port.
What you can do:
- Connect with the baud rate, parity, data bits and stop bits required by your device.
- View sent and received bytes as HEX or text in the serial log.
- Decode matching RTU read responses using byte offsets, data types and byte orders.
- View decoded values in a table or chart and export the results to Excel.
Prepare Frames with the RTU Tool
- Generate an RTU request, turn off Modbus Mode, enable HEX Mode, then paste the request into the send field.
- Generate sample RTU read responses and save them as hex text to test file parsing.
- Suggested workflow:
- 1. Match the serial settings and connect to the device.
- 2. Prepare a read request using the device register map.
- 3. Choose a polling interval appropriate for the device.
- 4. Set the response address, function code and parsing rules.
- 5. Check decoded values in the table or chart.
- 6. Export the results when you need to review them elsewhere.
Match the Device Settings
- Choose Select Serial Port and grant access to the intended device.
- Baud rate: match the value configured on the device.
- Data bits: use the device setting; Modbus RTU uses 8 data bits.
- Stop bits: match the device, including its parity configuration.
- Parity: match the device’s None, Even or Odd setting.
Read the Serial Log
- Display received bytes as HEX or text.
- Keep Latest Records removes older entries when the limit is reached.
- Record Limit sets how many entries to retain.
Send Data
- Enable HEX Mode to send the byte values in an RTU frame.
- Append CRLF adds carriage return and line feed; leave it off for binary RTU frames.
- Repeat Send sends the current request at the chosen interval.
- The interval is in milliseconds; allow time for the device to reply.
- RTU request examples:
- 01 03 00 00 00 0A C5 CD - Read 10 holding registers starting at address 0.
- 01 10 00 00 00 01 02 00 01 67 90 - Write the value 1 to one holding register using function 16 (0x10).
Decode RTU Read Responses
Choose a Data Source
- Serial: parse responses received from the connected device.
- File: parse saved binary bytes or hex text.
Choose the Data Format
- Binary Bytes：Use for raw RTU frame bytes.
- Hex Text：Use for hexadecimal text, such as 01 03 0C 40 48 F5 C3 00 00 01 3A C6 FE FF FF 39 D4.
- Match the format to the source data. Parsing uses the selected device address and function code and requires a valid CRC.
Set Parsing Rules
- Byte offset: count from 0 at the first byte of the response payload.
- Data type: match the integer or IEEE 754 register format in the device manual.
- Byte order: match ABCD, DCBA, BADC or CDAB to the device register map.
- Coefficient: multiply the decoded value by this scale factor.
- Constant: add this offset after applying the coefficient.
- Decimal places: choose the displayed precision.