Specifications

60
Schneider Electric
The Modbus Protocol (continued)
Principles used
Synchronisation of exchanges
Any character received after a silence of more than 3 characters is considered the
beginning of a frame.
Note: Be sure to leave a silence of at least three character between frames.
Presentation of frames
Presentation of query and response frames
b Query
b Response
E52352
End of stop bit
Beginnin
g
start bit
3-character silence
Character
Character
The contents of the following frames
is given in hexadecimal.
E52353
1 byte 1 byte n bytes 2 bytes
Slave no.
(1 to FF)
Function
code
Information Control word
The slave receives
the message, reads the
control word and accepts
or refuses the message.
Information required for
the query: address bits,
bit value words,
number of bits words,
number of words.
This code is used
to select the commands
available.
1 byte 1 byte n bytes 2 bytes
Slave no.
(1 to FF)
Function
code
Information Control word
Value of bits or words read,
value of bits or words written,
number of words or number of bits,
diagnostic.
Guide to Integration
Modbus / Jbus