Modbus Protocol
RTU
In RTU mode the protocol starts with a pause of 3.5 character times, 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 Byte |
t1-t2-t3-t4 |
ASCII
In ASCII mode the telegram starts with a colon (":", character 0x3A), and ends with a carriage return and a line feed ("CRLF", character 0x0D and 0x0A). The characters transferred are represented in the ASCII code.
|
Start |
Slave Address |
Function |
Data |
LRC |
END |
|---|---|---|---|---|---|
|
1 Byte 0x3A |
2 Byte |
2 Byte |
n Bytes |
2 Byte |
2 Byte 0x0D, 0x0A |