<Toc> <Ind>
<5. Modbus/RTU and ASCII Communication Protocols>
5-3
IM 77C01E01-10E
5.1.1
Configuration of Message
Messages sent from the higher-level device to the PR300 consist of the following elements.
Number of bytes
in RTU mode
None
Number of bytes
in ASCII mode
2
2
(1)
(3) (4)
(5)
(2)
(6)
Element
Station
Number
(ST-NO)
Function
Code
Start of
Message Mark
Data
Error Check
End of
Message Mark
None
1
2
2
4n
(variable)
1
1
2n
(variable)
2
(1)
Start of Message Mark
This mark indicates the start of a message. Note that only ASCII mode requires a
colon (:).
(2)
Station Number (01 to 99)
Station numbers are used by the higher-level device to identify the PR300 at the
communication destination. (These numbers are identification numbers specific to
individual PR300, which are expressed in hexadecimal in the message.)
00: Broadcasting mode (See subsection 5.1.5, “Specifying Broadcast”)
(3)
Function Code (See section 5.2, “Message and Response”)
This element specifies a command (function code) from the higher-level device.
(4)
Data
This element specifies D register numbers, the number of D registers, parameter
values, or others in accordance with the function code. (It is expressed in hexadecimal
in the message.)
(5)
Error Check
In RTU mode:
Carried out by the cyclic redundancy check (CRC-16) system.
In ASCII mode:
Carried out by the longitudinal redundancy check (LRC) system.
(6)
End of Message Mark
This mark indicates the end of a message. Note that only ASCII mode requires CR +
LF.
Содержание PR300
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