The Modbus Protocol; Ascii; Rtu - Beckhoff BC7300 Manual

MODBUS
ASCII frame
RTU frame
26

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
1 2
charact charact
er ers
:

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
T1-T2- 1
T3-T4 charact
er
Functio Data LRC
n
2 n 2
charact charact charact
ers ers ers
Functio Data CRC
n Check
1 n 2
charact charact charact
er ers ers
END
2
charact
ers
CRLF
END
T1-T2-
T3-T4
BC7300