Communication with Siemens S7 300, without using a CP card.

kahorn03

Member
Join Date
May 2006
Location
Kristiansand
Posts
14
Hi!

I’m currently learning to program with Siemens S7 300 series plcs.

As part of a project we are to link two 313C CPUs.

What kind of options do we have?

I have read through the main document under communication at the siemens automation support page; http://support.automation.siemens.com/WW/llisapi.dll?func=cslib.csinfo&lang=en&objid=20982954&caller=view

What I understand is that we have two options as long as we don’t have a CP card.

This is using the PB S7 basic protocol using the IPUT/IGET or using the PB-DP protocol?

The underlying documentation at the communication folder does not explain the setup for these two protocols…at least not without using a CP card, so I hope you guys can help me out here a bit.

I’m not even sure how to cable up these two into a network. The only network connection the CPU’s have is a MPI plug, so I don’t really understand how these two can be connected using Profibus without buying an additional CP card or something.

That said how, difficult is this task really?

Any useful links etc will be grately appreciated!

Regards

Kahorn03
 
Hello Kahorn;

If the CPUs you use do not have an integrated DP port, you will need a Profibus CP to exchange data between them (over Profibus, of course).

Depending on the amount of data you need to exchange, you can use different types of MPI connections between the CPUs:

MPI_exchanges.jpg


The simplest is Global Data; it also holds the smallest amout of data. You simply configure the exchange table in Netpro, after selecting the MPI network line, and right-click, Global Data.

All the others(Put/Get,BSEND/BRCV) are FCs available from the communication libraries or SFBs (Xput/Xget are SFC67 and SFC68; IPUT/IGET are SFC72 and SFC73, USEND/URCV are SFB8 and SFB9) from the System function blocks library in Step 7.
The online helpf for thes e functions is quite good, so just check inside your Step 7 program. For the "bilaterally connected" functions, you have to create a connection between the 2 MPI partners in Netpro, then use the connection ID in the programming of the functions.

Hope this helps,
Daniel Chartier
 
Last edited:
Hei Kahorn03.

"S7 basic communication" is the same as MPI.
Global Data is also only possible with MPI.
If MPI is OK for you, then this is the easiest way to go.
The limitations are that the baudrate is not so high, that there is no galvanic isolation between the two CPUs, which in turn means that you should only use this solution over short distances (under 50m).

You cannot use "S7 communication" with the onboard DP ports on two S7-300 CPUs.

The alternative is to use Profibus DP.
Either setup one CPU as master, and the other as slave,
or setup both CPUs as masters, and then insert a DP/DP coupler between the two CPUs.
You then have higher speeds and distances than with MPI.

edit:
I didnt read the part about that there is only an MPI port onboard. I though that you had 313C-2DPs, not 313C CPUs.
With these CPUs you only have MPI unless you install some kind of CP.
 
Last edited:
Hei!
Thanks a million to you two!
Help in a situation where your hair is about to turn gray, cannot be overestimated!:geek:

I've scrolled through the "configuring hardware" pdf in the s7 documentation folder and I recon chapter 11; global data will come in handy.
However I dont understand how I connect these two CPUs in a MPI network. I though I had seen this Profibus couloured cable with an Y connection to connect the two MPI connectors on the CPUs and one to the USB-PC adapter. However my tutor (who's not a specialist on PLCs by the way) thinks this only works for PC communication, as one unit can just send at a time.
Not thinking about it when discussing it, but this is what the GD rings are for?
As you understand I'm not sure how to connect the two CPUs in a MPI network, and I cannot find any documentation on it.
I'll be grateful for any tip!
Thanks!:site:
 
Hei igen kahorn03.

MPI and Profibus cables are exactly the same.
Profibus connectors allows you to daisy-chain from one station to another. Only 2 wires are wired through to all stations.

For a PC adapter (serial or USB) you need additionally 24V that is drained from the port on the PLC.
Therefore there are special Profibus connectors with a "PG socket" sitting piggy-back on the top. You connect the PC adapter to the PG socket when the connector is sitting plugged in the CPU.
One type is the 6ES7972-0BB41-0XA0. Without the PG socket it is slightly cheaper - 6ES7972-0BA41-0XA0.

By the way, be sure that the distances are not so long as there is no galvanic isolation in the MPI ports on the S7-300 CPUs. If you have long distances, post here again.

About the global data, I am sure that it works with S7 PLCs.
 
Hei Jesper! :geek:
(y)
I'm about to buy in the stuff, and just wanted to be sure that I've got this right:
The 6ES7972-0BB41-0XA0 http://www.luconda.com/artikeldetails/27/25/03/9309295-2-Siemens-6ES7972-0BB41-0XA0.html?ShopID=1 adaptor is plugged into the sub-D connector on the CPU, wheras the sub-d connector from the usb pc-adapter is connected to the back of this first adapter. The connection between the CPUs is two Profibus FC standard cables which are mounted in the first adapter, right?
Is it possible to use a custom two wire copper cable?
The reason for exchanging in this case is that I only need a meter cable in between the CPUs, and I've only found shops selling in 100 meter rolls.

Note to others who needs info about profibus (7MB pdf): http://www.automation.siemens.com/download/internet/cache/3/1392311/pub/en/04_PROFIBUS.pdf
 
Last edited:
Hei kahorn03.

The 6ES7972-0BB41-0XA0 http://www.luconda.com/artikeldetai...0.html?ShopID=1 adaptor is plugged into the sub-D connector on the CPU, wheras the sub-d connector from the usb pc-adapter is connected to the back of this first adapter. The connection between the CPUs is two Profibus FC standard cables which are mounted in the first adapter, right?
Correct.

At 187.5 kbaud and only 1 meter the requirements for the cable are not so stricht. You can use basically any 2-wire screened cable. The only problem may be to get the connectors to "bite" into the cable if it is not the same diameter as a Profibus cable.
 
Hi Jespermp

I Want To Know What Does It Mean This Abbreviation ( Cp) , And What The Defference Between It And The (cpu) ?

Thanks For Your Help

Maher
 
Hi Maher.
Please keep in mind that this reply is posted by a plc noob, but I think its safe to say that the CP is a network addon to be able to use the PLCs in network.
The CPU is the PLC itself. Its the same prinsiple as a computer I guess. The CPU processes the inputs and outputs, and acts accordingly to the program you write.
Some CPU models have network devices for, for example Profibus integrated. Other models don't, and you thereby might have to buy in a CP card.
 
kahorn03 said:
Hei!
Thanks a million to you two!
Help in a situation where your hair is about to turn gray, cannot be overestimated!:geek:

I've scrolled through the "configuring hardware" pdf in the s7 documentation folder and I recon chapter 11; global data will come in handy.
However I dont understand how I connect these two CPUs in a MPI network. I though I had seen this Profibus couloured cable with an Y connection to connect the two MPI connectors on the CPUs and one to the USB-PC adapter. However my tutor (who's not a specialist on PLCs by the way) thinks this only works for PC communication, as one unit can just send at a time.
Not thinking about it when discussing it, but this is what the GD rings are for?
As you understand I'm not sure how to connect the two CPUs in a MPI network, and I cannot find any documentation on it.
I'll be grateful for any tip!
Thanks!:site:

HI I ve never tried connect pls's with MPI but i found this maybe it will help http://paginas.fe.up.pt/~pportuga/plcs/siemens/Redes/misc/Communication-with-Simatic.pdf
 

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