Multiple Connections Via Port 502 - Siemens SIMATIC S7 Manual

3.6

Multiple Connections via Port 502

General
Pre-requisits
Number of
Connections
Displaying the
Status of the
Connection
Characteristics of
the Error Handling
Tip for your User
Program
OPEN MODBUS / TCP communication via CP343-1 and 443-1
2XV9450-1MB00; Manual edition 4.3
Some CP modules are able to multiplex TCP connections. In doing so several
Modbus clients can establish a connection via port 502. The CP acts as
Modbus server.
Here you can find information which CP and which firmware release support
multiple connections via port 502:
www.siemens.com/s7modbus
To use the functionality, the parameterization must be carried out as follows:
•
CP is server
•
port 502 as local port
•
unspezified TCP connection in NETPRO
•
passive connection establishment
Please note that only 1 connection is parameterized in NETPRO irrespective
of the number of clients which address the CP as server.
The CP is capable to keep up to 8 connections to different clients. A ninth
attempt for connection establishment will be rejected.
The status of the connection is displayed even in NETPRO online as well as
in special diagnosis of the CP.
As only 1 connection is parameterized in NETPRO, the display shows the
status of all TCP connections to the several clients.
As long as no client has established a connection "Passive connection
establishment in progress" is displayed.
As soon as one client has established a connection "established" is displayed.
It is not possible to check how many clients have actually established a
connection to the CP.
The FB MODBUSPN and the CP respectively must terminate and reestablish
the connection in certain error situations. This action is carried out by the FB
MODBUSPN. Thereby all existing connections via port 502 are terminated.
When several connections are established via port 502, it is not possible to
identify the client which has sent the recent request.
If the clients use different UNIT numbers, the verification of the same in the
user program allows a determination.
Commissioning
3-12