S7 Profibus communication

[dsc]

Hi Guys I have one panel which using S7315-2DP and about 31 profibus station. For power supply at site is using Generator Set and it seem not so stable and sometime we have voltage fluctuation that causes profibus station OFF and ON again in just 1 or 2 seconds. And because of that the CPU go to Stop mode due to I/O access write error, Is there any block i should add In so CPU can go to Run mode by itself (refresh) after all profibus sation OK. For now i already put in OB82, OB86, OB85 and OB122. Regards dsc

[JesperMP]

Hi dsc. The absolute limit is 32 nodes per segment. How many is your "315 + about 31 profibus stations". Also, try to provide detailed information about you network layout. About the generator problem, then I suggest you look into 24V UPS. Siemens has a range that is not so expensive. You seem to have all the relevant error OBs. Maybe your scantime was exceeded. Try to select "no OB85 callup at i/o error". Try to investigate the diagnostics buffer.

[dsc]

Hi Jesper What do u mean by 32 nodes per segment? I have here 31 nodes which 9 nodes inside main panel and the others on the machine and go thru a repeater. My CPu scantime about 75msec and it seem quite high. Where can i select 'no OB85 callup at i/o error'?

[JesperMP]

A segment is a Profibus line from end to end that is not seperated by a repeater. A repeater separates segments. The specification is that you can have max 32 nodes within one segment. It seems that the original system designer (*) has taken this into account as he has installed a repeater. *: It cannot be you, otherwise you wouldnt ask such a question. To disable the OB85 callup, go to the CPU properties - Cycle/Clock memory tab. To know for sure why the CPU goes into stop, investigate the diagnostics buffer.

[dsc]

Jesper, Yes u are correct, i m not the real designer and now i understand about it. Anyway thanks for ur help regards dsc