MODBUS
26
BC7300
The MODBUS Protocol
ASCII
In ASCII mode the telegram starts with a colon ( : ) character (0x3A), and
ends with a carriage return and a line feed (CRLF) (0x0D, 0x0A). The
characters transferred are represented in the ASCII code.
Start
Addres
s
Functio
n
Data
LRC
END
ASCII frame
1
charact
er
:
2
charact
ers
2
charact
ers
n
charact
ers
2
charact
ers
2
charact
ers
CRLF
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
Addres
s
Functio
n
Data
CRC
Check
END
RTU frame
T1-T2-
T3-T4
1
charact
er
1
charact
er
n
charact
ers
2
charact
ers
T1-T2-
T3-T4
