YOKOGAWA VZ20X, User Manual

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IM 77V01B01-01EN 5th Edition: 2023.03.07-00
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Network frame configuration
The Modbus/TCP frame configuration is as follows.
MBAP Header (Modbus Application Protocol Header): Header for identifying that the
protocol is Modbus/TCP
PDU (Protocol Data Unit): Body of data communication
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MBAP Header configuration
The MBAP Header comprises the following seven bytes.
Byte No. 0 1 2 3 4 5 6
Description Transfer ID Protocol ID Number of bytes Unit ID
Transfer ID: Specify any value for identifying transactions on the host device. The
VZ20X returns the value received from a PC/PLC as the response.
Protocol ID: Specify "0" in the case of the Modbus/TCP protocol.
Number of bytes: The number of bytes from the unit ID (byte No.6) onwards.
Unit ID: Specify "1" on the host device. "1" is returned from the VZ20X, too, as the
response.
MODBUS TCP/IP ADU
PDU
MBAP Header Function code Data