LS SV-iS7 Series - 8. Inverter Communication Address; 9. Modbus;TCP Frame Structure; MBAP Header and PDU Composition

iS7 Ethernet Option Manual
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8. Inverter Communication Address
See Chapter 11. Communication Function, Inverter IS-7 Manual.
9. Modbus/TCP Frame
(1) Modbus/TCP Frame Composition
Generally, Ethernet uses Ethernet II Frame.
MODBUS Application Protocol Header (MBAP Header)
MBAP Header constitution is presented below.
Protocol Data Unit (PDU)
This is the practical data of the Modbus TCP consists of Function Code
and Data.
Details will be described in the “(2) description on the Function Code”
below.
(2) Function Code Description
Modbus TCP is divided into Client and Server. The Client gives
command and the Server responses to the command. Generally,
Clients can be PLC, HMI, or PC and the Server is the inverter.
MBAP Header( 7 bytes)
PDU (5 bytes ~)
Section
Length
Description
Transaction
Identifier
2 Bytes
Unique transmission number, which is
increased by 1 each time the Client sends
Data Frame to the Server.
Protocol Identifier
2 Bytes
Fixed at 0.
Length
2 Bytes
The Data Frame length of the Modbus,
representing the length (in byte unit) from
the Unit Identifier in the MBAP Header.
Unit Identifier
1 Bytes
When the Modbus TCP and Modbus RTU
are connected via gate, Slave number is
indicated. If Modbus TCP only is used, this
is fixed to 0xFF.