VIPA System 200V IM Series, Manual

Page: 324 / 348

Chapter 8 Ethernet coupler
Manual VIPA System 200V
8-20 HB97E - IM - Rev. 06/29
ModbusTCP
ModbusTCP is a Modbus protocol put upon TCP/IP, where the IP address
serves the addressing. The ModbusTCP allows a client-server-
communication, several clients may be provided from one server.
The request telegrams sent by a master and the respond telegrams of the
slave have the same structure:
ModbusTCP Slave address
Function code Data
6Byte-
Header with
number of
following Bytes
1Byte data 1Byte data max 254Byte
For send and receive telegrams, ModbusTCP uses a header of 6Byte with
the following structure:
ModbusTCP header
Byte Name Description
0 Transaction identifier (High-Byte) Is sent back by the server (user-defined)
1 Transaction identifier (Low-Byte) Is sent back by the server (user-defined)
2 Protocol identifier (High-Byte) Always 0
3 Protocol identifier (Low-Byte) Always 0
4 Length field (High-Byte) Always 0 because messages < 256Byte
5 Length field (Low-Byte) Number of following bytes
Normally, Byte 0 ... 4 have the value 0. You may also increase Byte 0 and
1 in the slave and thus establish an additional control.
General
Telegram
structure incl.
TCP/IP
ModbusTCP-
Header (6Byte)