278 • ETHERNET
Network communication
Modular I/O System
ETHERNET TCP/IP
5.2.3 Application
protocols
In addition to the communication protocols described above, various applica-
tion protocols are implemented in the WAGO ETHERNET Coupler. These
protocols allow the user easy access to the fieldbus nodes:
>
a MODBUS/TCP server,
>
a BootP client and
>
an HTTP server.
5.2.3.1 MODBUS/TCP
MODBUS/TCP is a manufacturer-independent, open fieldbus standard for di-
verse applications in manufacturing and process automation.
The MODBUS/TCP protocol is a variation of the MODBUS protocol, which
was optimized for communication via TCP/IP connections.
This protocol was designed for data exchange in the field level, i.e. for the ex-
change of I/O data in the process image.
All data packets are sent via a TCP connection with the port number 502.
The MODBUS/TCP in the WAGO ETHERNET fieldbus coupler/controller
allows digital and analog output data to be directly read out at a fieldbus node
and special functions to be executed by way of simple function codes from
three stations simultaneously.
i
More information
Please refer to Chapter 6 "Common MODBUS functions" for a detailed de-
scription of these functions and their application.
MODBUS TCP segment
The general MODBUS/TCP header is as follows:
Byte:
0
1
2
3
4
5
6
7
8 - n
Identifier
(entered by
receiver)
Protocol-
identifier
(is always 0)
Length field
(High byte, Low
byte)
Unit
identifier
(Slave
address)
MODB
US
function
code
Data
Fig. 5-12: MODBUS/TCP header
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More information
The structure of a datagram is specific for the individual functions and is,
therefore, also explained in Chapter 6 "Common MODBUS functions".