ModbusTCP. VIPA IM 253-1NE00

Chapter 3 Deployment

Manual VIPA System 200V

ModbusTCP

General

Telegram structure incl.

TCP/IP

ModbusTCP is a Modbus protocol put upon TCP/IP, where the IP address serves the addressing. The ModbusTCP allows a client-servercommunication, 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

ModbusTCP-

Header (6Byte)

For send and receive telegrams, ModbusTCP uses a header of 6Byte with the following structure:

Byte Name

0

1

2

3

4

5

ModbusTCP header

Transaction identifier (High-Byte)

Transaction identifier (Low-Byte)

Protocol identifier (High-Byte)

Protocol identifier (Low-Byte)

Length field (High-Byte)

Length field (Low-Byte)

Description

Is sent back by the server (user-defined)

Is sent back by the server (user-defined)

Always 0

Always 0

Always 0 because messages < 256Byte

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.

3-18 HB97E - IM - RE_253-1NE00 - Rev. 12/44