S7-300 Siemens PLC

HI Everyone,
I have an application where i have 2 CPU315-2DP talking to each other directly using the profibus DP. i would appreciate it if you could send me an example on how to use SFC72 and SFC73 to enable them to talk to each other, any other suggestions are welcome (I did manage to use SFC14, 15 but i don't want that method).
Many thanks for your help.
Kader
Note my email address is : [email protected]

I_GET and I_PUT only work with socalled "S7 Basic Communicaton", which is another way of saying "MPI". In other words you cannot use it for a Profibus connection.

Exactly what hardware setup do you have ?
How are the two PLCs setup for communication ?
What do you want to achieve ?

Hi Jesper,
I really appreciate your quick response. I haven't used siemens plc's for 6 years, i am going to undertake a project using Siemens plc's talking to each other via profibus ( They are going to put one s7-300 as a master talking to all slaves which are s7-300, hmi's, festo valves..etc). So, before doing that i am doing some tests to get usedto siemns plcs. I have a CPU315-2 DP set as a master and a CPU314C-2DP set as a slave connected to each other via profibus DP (No CP's involved). Now i want to send and receive a datablock which contains let's say 60 words to the slave.
Note: I don't want to add any program in the slave (except configuring it as a slave and ofcourse the address config).
I did manage to use SFC72, which gave me RET_VAL = 7000 (but could not get them to talk), but now i understand from your answer that i can't use SFC72 when talking profibus.
Any other suggestions would be highly appreciated.
Many thanks for your help.
Kader

With the constraints given, SFC15 DPWR_DAT seems to be your only option.
Actually, DPWR_DAT is only necessary if the data have to be consistent. With 60 datawords, I think it is agood idea to use DPWR_DAT.

Obviously it shall be possible to get it to work.
Did you go through all the steps of defining i/o areas for both the slave and the master ?

By the way, I doubt that the HMI's are really slaves per se. They are probably also masters on the Profibus network.
Be sure to integrate everything into the same STEP7 project. This to ensure that the Profibus parameters are calculated correctly.

Just noticed that maybe there is a problem with a length of 60 words.
In the help text it seems that there is some kind of limitation depending on the terget. For an S7-400 is is 32 bytes. It is not clear what the limitation is with an S7-300.

Do you have to transfer the data "consistently" ?
If not, accessing it via the normal i/o adresses could be a simple solution.

Hi Jesper,
Thanks al ot for the information. Sorry the HMI's are not slaves !!. I have already used SFC14 and SFC15 together but unfortunatly i read somewhere i don't know where that i can only write 3 or 4 words at a time, this is the reason iwas trying to see if anyother methods. it did work transfering 3 words but did not try 60 words yet. I thought to post my question to get other ideas as i haven't used siemens for a long time.
I have just got your other message, i am going to try 32 bytes and more and see if it works or not. I will let you know with the outcome.
Thanks again for your help.
Kader

Hi,
Tried it and you are absolutly right you are limited to 32 bytes, even using the S7-300. I will have to look for another SFC to be used (I had a look at SFC65, 66, 67 and 68), i will have to give it a go and see if i can transfer more than 32 bytes.
In your message you mentionned that if the data is not consistent i can access it via i/o addresses, sorry may be a silly question but i don't know how ? If you notice in the hardware configuration you are limited to 16 words ie: 32 bytes. So, using the standard i/o as you mentionned do you ignore the hardware config where we specify the output and input addresses, also the length ??
Thanks again for your help
Kader

kader said:

So, using the standard i/o as you mentionned do you ignore the hardware config where we specify the output and input addresses, also the length ??

Click to expand...

No I meant just use the i/o addresses without using DPWR_DAT. I thought that maybe the limitation was with DPWR_DAT and not the HW config.
I have never configured a master/slave interface between 2 PLCs where needed a lot of data. So I have no experience with the limits.

Is it possible to configure more than one DP i/o area per PLC ? (Just throwing in an idea).

What are you requirements for speed ?
You could create your own datatransfer function. You could send one dataword + an index value per cycle. Thus you would only need 2 words in one direction and 1 word as feedback.

Forget the "X_" SFCs. They are for MPI also.

Hi,
Thanks for these information, they are very helpfull for me, I tried the SFC67, SFC68 no data transfered which confirms your statment but the annoying bit, it does not give you an error, it just give you the RET = 16#7000 which means no data blocks in the queue !!!
The indexing method is the only way i could see now but my last question on this is " are there any other SFC's or methods to be used for tranfering data using the profibus DP between masters and slaves where we can transfer more than 60 bytes ??!!
Another question that's nothing to do with this application, I have worked for rockwell for a long time and i am used to their product. They have this option of a backplane ( ie: you can browse networks starting from one network and going thru all other networks and see all attached plc's, cards, hmi's..etc).
Has siemens got similar thing, for example in my application i am connected to the master thru the MPI, can i download or browse the program in the slave where i am still connected to the master via mpi ?
Sorry i bombarded you with questions but in return, iwill be more than happy to help in any issues that you will face hopefully no isssues but unfortunatly we are in the real word and problems exist all the time
My stronguest point is Drives, so any issues on them please get intouch.
Thanks
Kader

kader said:

are there any other SFC's or methods to be used for tranfering data using the profibus DP between masters and slaves where we can transfer more than 60 bytes

Click to expand...

I think not, but dont take my word for it. I may have overlooked something.
Actually the onboard DP ports are great for the typical normal kind of application, like slave i/o, drives and maybe also HMI's. The weak spot is PLC to PLC communication. In other words, you get a lot for your buck, but then there are some hard limits.

kader said:

i am connected to the master thru the MPI, can i download or browse the program in the slave where i am still connected to the master via mpi ?

Click to expand...

I think yes. S7 has a quite good concept of "routing". You will have to set a "Test, Commisioning, Routing" selection under the Operating mode of the DP port on the CPU that has to be a DP slave.
I think that it will extend the cycle time on the slave though. Read the online help.
Apart from that, it takes more steps that what you are accustomed to in ControlLogix. You have to setup a "PG/PC station" in the STEP7 project. Follow the instructions on Siemens support site.

An unwanted comment is that I think that this setup will work, but there are so many limitations and it takes more effort. A much more future proof solution is to use Ethernet enabled CPUs everywhere, and then separate the supervisory comms (HMI, PLC to PLC) from the lower level (i/o, drives). It will be more expensive in the beginning, but will pay off in the long run.

I will probably need your drives expertise sometimes