Yokogawa PR300 Power and Energy Meter - Manual (Page 98)

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<Toc> <Ind> < 6. Modbus/TCP Communication Protocol>
IM 77C01E01-10E
6.3 Network Frame Structure
The Modbus/TCP frame structure is as follows:
MBAP Header Function code Data
PDU
MODBUS TCP/IP ADU
MBAP Header (Modbus Application Protocol Header) : Header used to identify the Modbus/TCP protocol
PDU: simple Protocol Data Unit
6.3.1 MBAP Header Structure
The MBAP Header (Modbus Application Protocol Header) consists of the following seven
bytes.
Byte No 0 1 2 3 4 5 6
Transaction ID Description Protocol ID Unit ID Number of bytes
Transaction ID: Set any value for identifying the transaction. The PR300 returns a value received from a higher-level device
as a response.
Protocol ID: Specify “0” for the Modbus/TCP protocol.
Number of bytes: Number of bytes after the unit ID (byte number 6)
Unit ID: For the communication with the PR300 itself, specify “01” for the higher-level device. The PR300 returns “01” as a
response. For the communication with the device connected to the RS-485 communication terminals of the PR300
using the Ethernet-serial gateway function, specify its station number (02 to 99). The device returns the same value as
a response.
6.3.2 PDU Structure
The PDU (simple Protocol Data Unit) consists of the following n bytes.
Byte No 0 1 to (n-1)
Function code Description Data
Function code: Specify a command (function code) from a higher-level device.
Data: Specify D register numbers, number of D registers, parameter values, or others in accordance with the function code.
(expressed in hexadecimal in the request)