S7 - MPI communication fails after modifying DP Bus addresses

RMA

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This ones got me really puzzled.

I decided to try out changing the DP-Station addresses, as mentioned in my other recent post. This involved re-addressing the CPU's DP Port to 26 instead of 2. However, the PC is connected via its CP5611 not to the DP Port but to the MPI Port, who's address has remained unchanged at 2.

When I tried to download the new version of the program I got a message that no active partners could be found. Since I hadn't changed anything as far as the MPI was concerned, this surprised me a bit, so I went back into HW-Config and checked everything over - it was all OK - then re-compiled it, just to be on the safe side. I then tried to download from HW-Config and as you can see from the screendump, the target has defaulted to the DP-Port at address 26. However, when I did a refresh, sure enough it found the MPI Port on address 2 and I was able to download the System data to the CPU.

So then I went back to Simatic Manager thinking that all would be well - but no change! It looks as though Simatic Manager is also defaulting to the DP-Port as well, but here you've no chance to search, it's just error message, end of story?

It was after this that I noticed some other peculiarities in the MPI Setup, but since that involves more Screendumps, I'll add that in another couple of Posts.

hwk_download.jpg
 
The other peculiarity is that in Simatic Manager under Extras -> PG/PC interface setup the interface is setup as CP5611 Profibus (active)

[attachment]

If I try to change it to CP5611 MPI, which would seem more logical, it doesn't work.

On the other hand in HW-Config, the situation is the other way round.

See next Post.

extras_pg_pc.jpg
 
As you can see under Properties, the MPI Port is here set to MPI and if I try to change it to Profibus to match the settings in Simatic Manager, again, it doesn't work.

[attachment]

So my two questions are:

1) How should I be setting up the MPI Port - in both Simatic Manager and HW-Config

2) What on earth is happening with the situation in Post #1 where I can download from HW-Config, but not from Simatic Manager - and what can I do about it?

Edit: I suspect that I can probably solve the problem if I set the MPI Port back to the MPI Adapter - even if it would be painfully slow, but that's not the point, I want to understand what's going on here.

Never having had any formal Siemens courses of any sort, I've had to learn everything as I went along, but this is my first real brush with networks, so I've probably got some very big holes in what I think I know!

hwk_mpi.jpg
 
Last edited:
Hi Roy,

the first part of your description is quite normal. Sometimes you have to use the refresh button (aktualisieren) when you have made a HW change in order to find the CPU and download the configuration.
I can speculate why it is so, but it is just like it is. Use the refresh button.

The rest I think is a bug in STEP7. It "cleverly" sees that you are making some changes with the Profibus port, and then "figures" that you want to connect via Profibus. It then reconfigures the CP5611 to Profibus, and you can no longer connect to the CPU, because it is on MPI.
 
About question 1:

The two places to set the MPI parameters should NOT affect each other (*).
The MPI settings for S7 port X1 is set in the HW config.
The MPI settings for the CP5611 is set with the Set PG/PC Interface utility (or in the manager).
That STEP7 oversteps its rank and messes with things without you asking for it, hmmmm.... You may have to demote it (downgrade to v5.2 maybe) ;)

*: Exception: If you have an integrated project with Simatic Net or Protool RT, then I think that the changes that are set one place will be automatically updated everywhere else in the project.
 
I changed the MPI over to address 26 as well and sure enough, everything is working happily now.

It does indeed look as though it's another case of S7 being too clever for it's own (or my) good! 🔨
 

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