S7 Profibus Communications

[malc cope]

Hi Just wondered if anyone has come across a small problem I am having connecting to a Profibus Network with my laptop, until recently I have had no difficulty connecting to the network which comprises a S7-314C-2DP cpu, 2 x TP170B HMI, 16 x SEW Movimot Drives & 2x Wago 750 Profibus couplers. The network itself appears to be working fine i.e HMI screens all work ok (navigation done by plc code), drives all start/stop & run at speeds as they should & remote i/o all reacts ok, the problem I am getting is although accessable nodes displays all connected nodes including the CPU, if I click on the CPU icon it only goes as far as displaying the blocks folder but clicking on the blocks folder only gives me a message that connection cant be made or words to that effect, if I go into the block off line then try to go online i get the same message. Occassionaly in accessable nodes in brackets next to the CPU is (waiting). I have spoken to Siemens technical support who tell me they have not seen that before. If I go to another similar but smaller (only 6 drives 1 hmi no remote io) network on the same site I can connect without any problems, I have been able to connect to the network I am having difficulties with before without any problems this is only a recent issue. One possibility I did think of although again Siemens say it should not make any difference is that 1 of the drives & 1 of the Wago units are due to site work going on are at the moment powered down so effectively they are not connected to the network, again though this has not previously caused problems. Any ideas? Regards

[JesperMP]

Hi malc cope. I can imagine 2 possible causes for your problem: 1. The CPU is running out of connection resources. With 2 HMIs only this does not sound likely though. If you go online via MPI, and then investigate the CPU communications tab, you should be able to see how many connections are used and how many are free. 2. The Profibus Token Rotation Time is incorrectly calculated. This can go well for some time because there is some "slack" in this value. Only when you try to attach your PC does it go wrong. Are the 2 HMI panels integrated into the same STEP7 project ? If not, have you taken these into account in some other way - for example by manually adjusting the Profibus Bus Profile ?

[malc cope]

Thank you I will investigate based on both comments next time I am on site Malc