Inter S7-200 Communication

[waynes 8]

Hi guys/ gals, Has anyone had an application where they have two S7-200 CPU's communicating to each other. This little PLC is very powerful on its' own, but it doesn't seem to communicate to another S7-200. My only other option is installing a Profibus DP master, and then doing the comms between that way. The information I need to get needs to be reliably sent and received. Kind of a Mininet system, on Siemens. I do have 2x S7-224 CPU's. I have heard that the two can talk (Point-to-point) by using some sort of a PPI link cable. Has anyone got this going? (Y/N) Also, was the comms stable? Thanks!!!

[Crossbow 294]

Well for one thing, the Profi block for S7-200 is a slave. But it can also be used for PPI communication between multiple S7-200 units or as a programming port. I've never set it up, but my understanding is you can use standard Profi cable and connect the two PLCs together with PPI. I would go try to get the manual for that module.

[waynes 8]

Thanks Crossbow, I heard that you could use one of the programming ports to accomplish this, without the need to buy the profi slave card. Has no-one done/ attempted this?

[waynes 8]

OK, Found the very cool solution to this. All under my nose!!

[krimson 0]

what did you find was your solution? this is the problem i am having.. i cant figure out to send data from one PLC to another... thanks!

[Gazzr 0]

I would guess the solution is MPI. But please come back and let us know. I have an idea for my plant where it would be good to send some data from one S7-200 to another, but I have never done this, so any experience of problems encountered and solutions would be great.

[krimson 0]

well what i am trying to do is send a VW900 from plc1 to plc3 and i was playing with the netw/netr functions, but they only send bits... not words... since i am actually moving C1 (a timer) into VW900 i was almost thinking of trying to send a bit with netr/w and hack a timer on the other end... but being a hack, its not a very good solution and will most likely get way out of sync and end up being far too much hassle than its worth. ive read about using global tables, but i am very unfamiliar with that.. i go on my symbol tables and in USR1 i make a VW900 entry, and then try and see if PLC3 reads the data, and it just reads as 0, so that is a no... im a little new at all of this, so i am a little more than lost!!!

[Gazzr 0]

I had intended to try and get 2 S7-200's communicating a while back. (Just for the sake of it), but never got round to it. This thread sparked my curiosity again, so I dug out a couple of profibus connectors and knocked a cable up. Wrote a small program for a s7-224xp that basically was an up down counter and a network to transfer the counter value to VW0, this value was then sent to PLC no2. The other plc was a S7-222, which I wrote a program that flashed outputs if value in VW0 (In S7-222) was above or below 5. Found it amazingly easy to do. Go to Tools> Instruction Wizard and select NETR/NETW. Tell it addresses and No of Bytes to be transferred from and to, and it does the rest. Very impressed. Just wish somebody at my company hadn't decided that we now should only use AB as I seem to get along with these quite well. Edited 1 Nov 2007 by Gazzr

[krimson 0]

that is exactly what i did, and now i can actually get information sent across, but i was a little hazy on what all to put.. so i did a netw on plc1 to plc3 and a netr on plc3 to plc1 and i see the data getting transferred, but its not holding its value... it gets a quick shot of the right data, then goes to zero... then it flashes again the right value, and goes to zero... i dont know if i need to have both the netw and netr if i dont need to send anythng BACK to plc1.. i just need it to read.. but, do i need a write on one end and a read on the other, or just a write on the one OR a read on the other?

[Gazzr 0]

I didn't use the NETR. Just used NETW on the 224XP. What cable have you got running between the two?

[Crossbow 294]

You should be able to use standard Profibus cable and connectors for multi-drop S7-200 comms. Terminate the ends.

[Gazzr 0]

I didn't have any profibus cable. So used some belkin 6 core - used 2 cores for the comms and tied all the others to earth. Only about 2' length though, but hey - it worked. I may have an application that would require a 60m - 75m cable run - if I were to do this I would get the proper cable. But would i really need a repeater? Or could I just keep the baud rate low and hope for the best?

[krimson 0]

i used profibus cable.. but i will play with it with only using the netw function... maybe having a read on one and a write on the other was throwing it off. i ended up using a quick fix by simply running a Q on PLC1 and 2 to an I on PLC3 (after proper 110/24v conversions) it works like i want it to, but i would like to be able to avoid that in the future.