S7 starts communicating with OPC server?


Thread Starter


Hi there, i have the following problem.

I have a Siemens S7 PLC with a CP 443-1 industrial ethernet card. I also have a OPC server from INAT (www.inat.de). I made a connection between the OPC server and the S7 via TCP/IP it works fine. My problem is that the OPC server is constantly polling for data change in the PLC (this affects network speed).

I want my PLC to connect to the OPC server by an event. for example my PLC is executing his program and there is an alarm, the PLC program detects the alarm and starts communicating with the OPC server which can log this alarm in a database via a OPC client.

my question is, is this possible? has anyone done this before?.. i've tried but i can't get it working..



Frank Iwanitz


the server polls the plc since there is an (at least one) active OPCGroup with a set UpdateRate and the MPI protocol is based on a Request-Response-Datagram (I guess). Therefor check,
- if there is a possibility that the plc can send an event to the server without being requested for this.
- The server can pass this information to the client
- the client activates OPCGroups and starts polling the data of interest.

If the plc can not send events to the server without being requested, define a boolean variable in the PLC and let the server only read this variable. If the variable changes it is passed to the client and the client can activate
the OPCGroups. But consider, this will take some time.