Modbus protocol
RTU
In RTU mode the protocol starts with a pause of 3.5 characters, and finishes in the same way (illustrated in the diagram with T1-T2-T3-T4).
The characters permitted for transmission in all fields are hexadecimal 0... 9, A..., F.
|
Start | Slave address | Function | Data | CRC | END |
|---|---|---|---|---|---|
t1-t2-t3-t4 | 1 byte | 1 byte | n Bytes | 2 bytes | t1-t2-t3-t4 |
ASCII
In ASCII mode the telegram starts with a colon (":", character 0x3A) and ends with a carriage return line feed ("CRLF", characters 0x0D and 0x0A).
The characters transferred are represented in the ASCII code.
|
Start | Slave address | Function | Data | LRC | END |
|---|---|---|---|---|---|
1 byte 0x3A | 2 bytes | 2 bytes | n Bytes | 2 bytes | 2 bytes 0x0D, 0x0A |