S7 PLC protocol

rkorem

Member
Join Date
Jan 2005
Posts
5
We have a requirement for S7 PLC driver. We would like to develop a communication driver for the S7 PLCs for our SCADA system. Could you please tell what kind of protocol is used? When I called the siemens customer support they told me that fetch/write protocol is used. But they did not provide any further information about this protocol. Could you please tell what kind of protocol is used and where can I download it? Thanks in advance.
 
The last thing that I heard about the S7-communication protocol was that it is a secret guarded like Fort Knox.I think that only Siemens can help you.
 
Hi rkorem,

with S7 there are basically 3 ways to communicate:

1. MPI. This totally proprietary. Some have made 3rd party drivers for MPI, but they all use the slow PC/MPI adapter. Only Siemens know how to use the faster CP5511, CP5512 or CP5611 cards.

2. Profibus. This is an open standard. To develop ones own driver is a monumental task. But it would pay off because you could connect to many different Profibus capable systems.

3. Ethernet. There are several ways to connect via Ethernet. One of them is called "RFC1006". It should be fairly simple. I say this because there are several 3rd party drivers that use RFC1006.

To you, I recommend to use OPC and not waste any more time with developing your own driver. If you are hell-bent on doing it yourself, then go via RFC1006.
 
I believe Siemens sell (of course) a software package named Prodave. As far as I know this is mainly a group of various runtime libraries with which you can write your own comms applications in C or similar. You embed calls to the library modules in your code and let them handle all the tricky stuff. I don't know how clever Siemens have made these modules and whether you can rewrite a new STEP7 based on this or not. My guess would be not. But it may be worth asking your local Siemens support about Prodave. (And remember, it's German. It ain't pronounciated "Pro-dayv". It's spokenised "Pro-dah-vuh")

Regards

Ken.
 
I may be wrong, but I think you have to purchase a license for each runtime seat that uses Prodave.
So I guess that it would pay off better to go via OPC, its an open standard and not proprietary like Prodave. Maybe rkorem's SCADA package allready has OPC client functionality allready.
I also think that it is quite cheap these days to use OPC. Siemens Softnet S7 Ethernet LEAN is inexpensive, and may be enough for rkorem (if there is Ethernet in the S7 systems he wants to connect to).
 
Have a look at
http://libnodave.sf.net
This project provides a library to communicate to S7 PLCs over MPI, PPI, ISO over TCP.
It can be used on LINUX and Win32 systems.
And the best: It is open source.
 
Thanks for your reply.

We may not be able to use the OPC Server as our SCADA system is in QNX operating system. could you please tell me where can I download the RFC 1006? Is there any library available for RFC 1006? Thanks
 
Sadly, I cannot locate a ready-to-run library for QnX. The closest is a Java library (!) from Langner.
A full source code is also not something you stumple upon.

Here are some other alternatives that may connect QnX with the world of Siemens:
Steinhoff specialises in QnX solutions for Profibus (amongst other things).
And HERE is a Profibus card from Applicom that also should work with QnX.

Good luck.
 
If you wont let the do-it-yourself ethernet option go, then it seems that the best source of documents is Siemens FAQs and MANUALs site. Searching for "Ethernet UDP" or "RFC1006" on this site provides a lot of valuable links.

But it will be long walk before you are at the final destination I am afraid.

Again, good luck on the journey ;)
 
I just had a quick look at QNX. As it is UNIX or Posix compatible, I think it should be possible to compile Libnodave on it with very few changes or even none.
 

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