S7-315 Pn/dp + Cp342-5

Hello,

I replaced an old S5-135 and four IM308 with a 315-2 PN/DP and four CP342-5. On each Profibus there are S7-300 and S5-95U slaves.
Now I have a little problem... the communication processor on one of these s5-95U slaves may fall down but CPU continues to run. So I have to switch off or reset the slave to relaunch the communication processor. What's going wrong ? (all the hardware has been renewed and checked).

I find your description a little confusing.

If one entire Profibus network is not working, you have to reset one of the attached slaves to get comms to all slaves up and running ?
That sounds odd.
If all slaves on one CP is not communicating, you can try to investigate the Hardware Diagnostics on the 315.

Or is that if one slave on one of the networks is not working, you have to reset that slave to get it up and running ?
That sounds logical.
If the affected slave is an S7-300 setup as intelligent slave, then look into the diagnostics buffer of that PLC.
Cant help you with S5-95U. Seriously you should plan for exchanging these with something newer.

Maybe you can try to program automatic disable and enable of the affected slaves. You use SFC12 for this.

How many DP slaves are there ? I just find it odd to install that many CP342-5's. All data still have to pass through the same backplane on the 315.
Maybe a single 317-2DP would have been a better choice, with each of the two available ports on the CPU handling one Profibus network.

It's only one s5-95U on one of the 3 networks that's falling down and it's not always the same...

Network 1: 1xS7-300DP; 8xS5-95U-DP.
Network 2: 7xS7-300DP; 2xS5-95U-DP.
Network 3: 1xS7-300DP; 2xS5-95U-DP.
Network 4: 16xS7-300DP.

The S7-315 says that this slave doesn't exist on the network...

Do you have some diagnostics capable adapter (like a CP5511, CP5512 or a CP5611) to see if the missing slave is present on the network ?
If it is present, you could try the SFC12 to diable/enable the affected slave.

Can you rule out noise or other problems ?
What is the busspeed ? You can try to run at 187.5k and see if that helps.

Did you check the manual for S5-95U with DP interface ? :
http://support.automation.siemens.com/WW/view/en/1091098
Chapter 8.5 describes some diagnostics that you could possibly investigate.