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Modbus frame decoder
Paste a hexadecimal Modbus RTU or TCP frame. Busloom identifies the transport and exposes the fields instead of reducing the frame to a single success or error label.
Spaces, line breaks, colons, and 0x prefixes are accepted.
Modbus TCPNo CRC · MBAP framing
Read Holding Registers frame addressed to Unit 1.
- Transport
- Modbus TCP · MBAP header
- Transaction ID
- 1 · 0x0001
- Protocol ID
- 0 (Modbus)
- MBAP length
- 6 bytes after this field
- CRC
- Not present · Modbus TCP uses the MBAP header instead
- Unit ID
- 1 · 0x01
- Function
- FC03 · Read Holding Registers
- Start address
- 0 · 0x0000
- Quantity
- 2
REFERENCE
How to read the result
A TCP frame starts with the seven-byte MBAP header. An RTU frame starts with the Unit ID and ends with a two-byte CRC sent low byte first. The function code decides how the remaining PDU bytes should be interpreted.
A valid CRC proves that the captured RTU bytes are internally consistent. It does not prove that the address, function, or decoded engineering value is correct.