serial S7 whthout OPC

[lv$vi]

I want to communicate a PC to a PLC(S7-300) with the serial port. 

some one said that i need the OPC to finish the communication between them,but i donnot have OPC and donnt want to buy it.

the client want me to do that with Profibus,but i donnot famillar with it,so do i need to know the protocol of profibus?

or can i use only VISA to do the job?

thanks for any suggestion!

[Jochen]

Even though the physical layer of Profibus is RS485, you can't run the protocol using a standard RS485 interface. The reason for that are the real-time timing requirements of Profibus. To meet this requirements you need a Profibus interface in your PC, that runs the protocol onboard with it's own processor. The profibus interface, that I have linked to before, comes with configuration software, an easy to use LabVIEW library, example code and a getting started tutorial, providing a good entry point to Profibus.

Kind regards,

Jochen Klier

National Instruments

[lv$vi]

Thanks Jochen a lot.

My client told me that they have the COMSOFT card . so i can communicate with plc by using the card.

but when the system start to work, i want to send a message to the PLC to activate it first , then i will do the communication between LabVIEW and PLC.

How could i send just a signal to start the PLC? can the VISA do this job?