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Parameterisation
Transfer value
When writing an ASCII telegram the transfer value must always be specified with V in front. When
reading, the transfer value is omitted and is returned as an answer.
Command end character
The command end character is not specified in this documentation because the need for a command
end character depends on the terminal software used.
7.3
Architecture of Modbus TCP
Parameter structure for sending via Modbus TCP
Modbus TCP is an open communication protocol with Client-Server architecture. The byte sequence is
based on the big endian system.
1 Modbus TCP header
2 Modbus TCP addressing function code 0x17
Fig. 5
Modbus TCP header
0 Transaction number
2 Protocol identifier
Fig. 6 Modbus TCP header
Byte
Num-
Designation
no.
ber of
bytes
0
2
Transaction number
1
14
3 Structure of Modbus TCP function and data
area function code 0x17
4 Number of following bytes
5 Device identification
Description
Freely selectable
Byte order
most significant byte
least significant byte
Festo — VAEM-V-S8EPRS2 — 2020-07
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