Siemens SIMATIC S7-1200 System Manual page 1180

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Communication processor and Modbus TCP

13.5 Modbus communication

CONNECT parameter assigns data used to establish a PROFINET connection

You must use a global data block and store the required connection data before you can

reference this DB at the CONNECT parameter.

1. Create a new global DB or use an existing global DB to store the CONNECT data. You

can use one DB to store multiple TCON_IP_v4 data structures. Each Modbus TCP client

or server connection uses a TCON_IP_v4 data structure. You reference the connection

data at the CONNECT parameter.

2. Name the DB and a static variable with a helpful name. For example, name the data

block "Modbus connections" and a static variable "TCPpassive_1" (for Modbus TCP

server connection 1).

3. In the DB editor, assign the system data type "TCON_IP_v4" in the Data Type column, for

the example static variable "TCPactive_1".

4. Expand the TCON_IP_v4 structure so you can modify the connection parameters, as

shown in the following image.

5. Modify data in the TCON_IP_v4 structure for an MB_SERVER connection.

6. Enter the DB structure reference for the CONNECT parameter of MB_SEVER. For the

example, this would be "Modbus connections".TCPpassive_1.

Modify TCP_IP_v4 DB data for each MB_SERVER connection

● InterfaceID: Using the Device configuration window, click on the CPU PROFINET port

image. Then click on the General properties tab and use the Hardware identifier that you

● ID: Enter a number between 1 and 4095 that is unique for this connection. Modbus TCP

communication is made using underlying TCON, TDISCON, TSEND, and TRCV

instructions, for OUC (Open User Communication). Up to eight simultaneous OUC

connections are allowed.

● ConnectionType: For TCP/IP, use the default 16#0B (decimal value = 11).

● ActiveEstablished: This value must be 0 or FALSE. The connection is passive in that

MB_SERVER is waiting for a communication request from a Modbus client.

S7-1200 Programmable controller

System Manual, V4.2, 09/2016, A5E02486680-AK