Siemens s7 modbus master

[dont panic]

I have to set up an S7 314 plc as a modbus master. I have the hardware/dongle/firmware but the sample projects don't give a lot away!. I am familiar with S7 although this is my first CP341 job. has anyone a project they could send me or a few pointers.? please don't say RTFM as Siemens manuals leave a lot to be desired!! Thanks

 

[dahnuguy]

What hardware did you use for the modbus connection to a siemens 314?

Would this one work for a 313C?

 

[Ned_Flanders]

Right! I did not get any replies for a month or so. So I struggled on and got there in the end. I am using a siemens cp341 rs 232 rtu interface card. This is not cheap (The card was £200 and the "Firmware" £700 or so) but it calls the data nicely and places it into a standard data block.

I do not see any reason why it will not work with a 313 cpu.

My set up is the first one I have programmed. I have a number of temperature and vibration sensors monitoring rotating plant condition. This data starts life as a 0 - 10v signal, is scaled into modbus, given an address then transmitted via a radio signal called zigby (A bit like bluetooth). This was cheaper that hard wiring.

The plc panel has the reciever in it, which is connected into the Siemens card. The data is displayed on a "Proface" TFT screen (Looks nice!)

I have another system on site, which uses a 3rd party "Converter" which is connected via Profibus. The cost of a profibus cpu and the German converter was the same as the Siemens kit.

If this helps, (Or not), or you need more info, let me know.

 

[dahnuguy]

So........what part is the Modbus converter for Siemens?

Is there a Modbus module that works with Siemens ?

I have an Ethernet module easy enough, and Profibus.

But the marketing "people" wont stop offering anything to anything communications.

 

[Ned_Flanders]

Well, the model is a CP341, but there are several types depending on which protocol modbus uses. Mine is Modbus RTU RS 232. You need to know this. I am not back to work till Tuesday, but if you look at a Siemens automation catalogue on line, the card is under communications.
You also need to know if it is a master or a slave. Mine is a master. In theory, you have to order the correct one, but I didn't. I ordered a "Slave" but wanted a "Master".
A quick call to Siemens automation UK, and they told me the dongle should work (It plugs in the back). And it does!They just emailed me a link to their "Master " drivers.

There are some sample programs in the library that comes with "Step 7".
I used theirs, and just modified it. I have only one slave, but the slave cannot address all the registers at once, so I just have a cycling program that calls the relevant datablocks/registers. I think the Siemens will do over 100. What do you actually want to do?

I hope this isn't too vague?


Markie

 

[dahnuguy]

Well see thats the rub ....I have no idea.

I walked into a project that was almost done after 9 months of work from 3 other people.

It started as a Siemens200 using WinCC and Micro-Win.

I had never used anything Siemens but I picked up these two in about a week.

Then everything changed and we had to switch to a 313C......and Step7.

SO I fight my way through Step7 , I have a handle on it after a month, but now we have to communicate with every known protocol on Earth .....because someone wrote it in the sales hand out.

OK ..............they come to me and say what do we need to do to communicate with Modbus?

I say buy a module , give it to me and then buy something with Modbus to test it with. MIght take a week to work out the bugs.

So then they want to know what to order.

I have never used any Siemens before this................I have no idea.

The A&D Mall is not easy to dig through but I found the 341 . I did not realize it would work with Modbus due to the crytic verbage from Siemens.

I suspose I need a 341 Slave module as I will be connecting to an existing Modbus network.

My answer was to supply ethernet and be done with it.

That is all I know.

I am gathering information to try to work something out.

No idea how to make this work without a Modbus in place to setup with.

Thanks for the information.

 

[Ned_Flanders]

I undestand a bit better. I "Googled" modbus, and got a reference guide, which was quite helpful. If all you have to do is be a slave (Perhaps certain bits change state as directed by the master) it may be straight forward, but I imagine to integrate this into an existing system, you will need to reprogram the master to call the new slave.

I am an end user, rather than an integrator, so I only get 2 or 3 large programming jobs per year. I posted here for general help, but as you saw - didn't get any!

I like to think I'm ok with S7 so if I can help I will.

 

[dahnuguy]

Hey thanks for the offer of help.

I suspect that you didn't get any responses because Modbuss isn't very popular around here.

There is a large AB and Siemens support group here, probably other areas too, I don't read the whole forum.

The part I don't get about the Modbus is difficult to describe.

I am used to working from the other direction. "Here is my plant and here is the new piece I will add to it." or "Here is your plant where I will add this piece of new stuff with full access to said plant."

On this project I am building a stand alone unit that works all by itself with no interaction necessary with the rest of the plant.

The only need to interface this unit would be for remote alarms and for gee whiz data collection. It is not part of the process and can not cause harm to personel.


I imagine that I would blkmove the alarms and maybe some level / temperature data to a DB and make that available to the Modbus network.

What they do with it is up to them.

Of course they will be calling every week wanting something added to the list and on and on, but realy, that's all I could do.

It will ship and they will plug it in and do the setup routine and then it runs. No on site tech to do startup. Something else that is new to me.

Maybe this is way easier than I originaly thought.

I think it is.

I put data in a DB and then just tell them which address is what and that's that.

It will be all read only as well so I don't need to even look at it in the program.

Just update the variables every so often and forget it.

Now to hammer out the requirements for hardware and firmware and software.

If the 341 is the hardware, I assume it must be set up for Modbus because it is not called a Modbus Module.

Then it needs to be added in the hardware profile.

Then a simple move instruction in S7 should put the data in place.

I hope it is that simple.

 

[Ned_Flanders]

Yes, I agree, all you need to do is move the alarms into a data block and tell the customer what their address is.

I think that ther are a few "Types" of modbus - you need to know what they are using.

 

[dahnuguy]

I started a new thread, instead of making a copy ....

http://www.plctalk.net/qanda/showthread.php?t=49659&highlight=s7+modbus