Modbus ASCII Online Tool

Modbus ASCII message parsing, command generation, response data generation, and LRC checksum calculation tool

Browser execution mode: Your data is processed in your browser and is not uploaded to the server.

Speed and Stability: Processing speed depends on your device and browser. For large batch work, the desktop version may be more stable.

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If the online tool fails to load or run, try the desktop tool.https://tools.yikeaigc.com/

Tool Usage

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Request Command Generator

Set slave, function code, address, and write data to generate a standard ASCII frame.

Auto LRC Supports 01/02/03/04/05/06/0F/10

Command ParametersSet First, Then Generate

Slave Address

Function Code

Start Address

quantity Register read range: 1-125.

Auto count by data Show CRLF frame ending

Coil Status

Write data type

Byte order

Write data Enter multiple coils bit by bit; enter multiple registers by the selected data type. In HEX byte mode, you can enter 00 64 00 C8.

ResultsWaiting to generate

ASCII message

Raw HEX

LRC

Length

Click “Generate command” to view the frame structure.

Field	HEX	Description

Response Message Generator

Generate response frames for read/write scenarios; select an exception code directly for exception responses.

Response parametersSelect a type first

Response Type

Slave Address

Function Code

Exception Code

Data Type

Byte order

Show CRLF frame ending

Response data For coils/discrete inputs, enter 0/1; for registers, enter by data type.

Address

Value/Quantity

Coil Status

ResultsWaiting to generate

ASCII message

Raw HEX

LRC

Length

Click "Generate response" to view the frame structure.

Field	HEX	Description

Message Parser

Enter a complete ASCII frame, validate LRC, then view the frame structure and data values.

Parse parametersAuto-detect supported

Message direction

Default Data Type

Default Byte Order

ASCII message

Custom Parse RulesOffset starts from the data area

Parse ResultWaiting to parse

Click "Parse message" to view the LRC and fields.

Field	HEX	Description

Item	Value	Description

#	Name	Position	HEX	Type	Parsed value

LRC Check

Enter HEX bytes or an ASCII frame to calculate LRC and generate a copyable full frame.

Parity SettingsSelect input format first

Input format

Last byte is original LRC Show CRLF frame ending

Input data

Calculation resultsWaiting to calculate

LRC HEX

LRC DEC

Low 8-bit sum

Full ASCII frame

Click “Calculate LRC” to view the calculation steps.

#	bytes	Sum low 8 bits

Batch processing

Paste multi-line text or choose TXT/CSV files; download as a ZIP after processing.

Batch ParametersFiles read locally

Mode

Default Data Type

Default Byte Order

Batch text Command mode format: slave, function code, address, quantity/value, write data. Function codes can be 03, 0F, 10, 15, 16.

Batch files Only the first 20 files are shown; all files will be processed.

Bulk ResultsWaiting

Load the sample first to check the format, then process your own data.

#	Source	Input	Results

Instructions

Software Usage Instructions

Request Command Generation: First set the slave address, function code, starting address, and quantity, then click “Generate Command”. Supports 01 Read Coils, 02 Read Discrete Inputs, 03 Read Holding Registers, 04 Read Input Registers, 05 Write Single Coil, 06 Write Single Register, 0F Write Multiple Coils, and 10 Write Multiple Registers.
Write Data Configuration:
- Single Coil: Select ON or OFF, and the tool will generate FF00 or 0000.
- Single Register: Enter a register value in the range of 0-65535.
- Multiple Coils: Enter 0/1 or ON/OFF, and the tool will pack the data according to Modbus bit order.
- Multiple Registers: Select UINT16, INT16, UINT32, INT32, FLOAT32, or HEX bytes, and set the ABCD, DCBA, BADC, or CDAB byte order.
Response Message Generation: Select a normal response or exception response. Normal responses can generate read responses and write confirmation responses; exception responses can select exception codes such as illegal function, illegal data address, illegal data value, and device failure.
Message Parsing: Enter a complete Modbus ASCII message, and the tool will verify the LRC and display the slave address, function code, data area, received LRC, and calculated LRC. You can add custom parsing rules to parse register data by offset position.
LRC Check Calculation: Enter HEX bytes or a complete ASCII message, then click “Calculate LRC” to obtain the HEX, DEC, low 8-bit checksum, and complete ASCII frame.
Batch Processing: You can paste multi-line text or select TXT or CSV files. Batch command generation, batch message parsing, and batch LRC calculation are supported. After processing is complete, you can download the ZIP results.
Save Settings: Common slave addresses, function codes, data types, byte orders, and parsing rules can be saved by clicking “Save Settings” for convenient reuse next time.

FAQ

A: A Modbus ASCII message usually consists of a start character colon (:), slave address, function code, data area, LRC check, and ending characters CR LF. The tool automatically generates the LRC and displays the raw HEX bytes in the results.

A: The LRC adds up the bytes of the slave address, function code, and data area, takes the low 8 bits, and then takes the two’s complement. The starting colon and ending CR LF are not included in the calculation.

A: When using 0F to write multiple coils, enter 0/1 or ON/OFF, and the tool will automatically pack the bits. When using 10 to write multiple registers, enter values according to the selected data type, or switch to HEX byte mode to enter raw bytes directly.

A: 16-bit data usually does not require cross-register byte order handling. 32-bit integers and FLOAT32 are affected by the device byte order. ABCD indicates big-endian, DCBA indicates little-endian, and BADC and CDAB are commonly used byte or word swap formats in vendor devices.

A: Common causes include missing content when copying the message, incorrect HEX character input, parsing an RTU message as an ASCII message, an incorrect LRC byte, or mistakenly including the start and end characters in manual calculation.

A: One record per line. The common format is: slave, function code, address, quantity/value, write data. For example: 1,03,0,10; 1,06,10,100; 1,10,30,,100 200 300.