YOKOGAWA UTAdvanced Series, User Manual

Page: 81 / 866

4-4
IM 05P07A01-01EN
4.3 Configuration of Network Frames
Modbus/TCP frames are configured as follows:
MODBUS TCP/IP ADU
PDU
MBAP Header Function code Data
MBAP Header (Modbus Application Protocol Header): Header for identifying that the
protocol is Modbus/TCP
PDU (Protocol Data Unit): Body of data communication
4.3.1 Configuration of MBAP Header
The MBAP header comprises seven bytes as follows:
Byte No 0 1 2 3 4 5 6
Content Transfer ID Protocol ID Number of bytes Unit ID
Transfer ID: The host computer specifies an arbitrary value for identifying transactions.
The UT75A/UT55A/UT35A/UP55A/UP35A returns the value received from the host
computer as the response.
Protocol ID: “0” is specified in the case of the Modbus/TCP protocol.
Number of bytes: Number of bytes from the unit ID (byte No.6) onwards
Unit ID: The host computer specifies “1” and the UT75A/UT55A/UT35A/UP55A/UP35A
returns “1” as the response. For the communication with the device connected to the
RS-485 communication terminals using the Ethernet-serial gateway function, specify
its communication address (2 to 99).
4.3.2 Configuration of PDU
The PDU (Protocol Data Unit) comprises n bytes as follows:
Byte No 0 1 onwards (n-1)
Content Function code Data
Function code: The instruction from the host computer is specified.
Data: The D register No. and number, parameter values, and the like of internal registers
are specified according to the function code.