Yokogawa PR300 Power and Energy Meter - Manual (Page 82)

<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.