PLC to PC communication

I'm using a Siemens s7 plc. I need to communicate the plc with the PC realtime i.e I have developed some screens in VB and I need to communcate with the PLC to update the screens constantly....like a scada application.... How do I retrieve data from the PLC ?????

You can use a Siemens software called Prodave you can comunicate via MPI beetwen PC in Visual Basic and DB of PLC, or you can use a serial card interface on the PLC eg.CP340 or CP341 and make a seial protocol beetwen Visual Basic and PLC, I think the second solution is the best because you can make your protocol without using a siemens software and PC adapter for the comunication, but is only my opinion.

Or, you can use ncdde.exe which is coming with the MMC103 software.
This is a DDE server, but I think also others (DDE servers) are available from Siemens. Anyway this solution, like the serial one, is not so fast (best PLC tag read time is ~ 10 ms), but the more PLC tags you need to read/write, the slower will become.

Hi Misha,

you can use something called OPC for the dataexchange. It is an open standard that have many vendors of socalled "OPC servers" (drivers) for various PLC brands.
An OPC server from Siemens (Simatic NET) will cost you €450.
Communication via MPI, DP, Ethernet.

An alternative is Prodave MPI, also from Siemens.
Communication via MPI only.
It comes in two variants:
Standard, will communicate via all S7 variables. For €250.
Lite, will only communicate via DB´s. For €150.

The MPI network is a proprietary Siemens standard. I think it is way too difficult for the average person to develop a driver.

You can do a search on the net and you will find some free activex controls or dll that u can use in your program. I don't know the name because I used them a while ago.