S7 using SFC43

[Heino Geerdens]

Hi all,

Here's my situation;
- I have a S7-318 -2, Every 10ms OB35 is called (priority 12). Recently, when I went online (MPI) the CPU went in Stop. De Diagnostic Buffer showed me a problem with the cyclic interrupt OB35 .
Because the execution time can't be changed, I was thinking about calling SFC43 in OB80 to avoid such problems in the future.
The only problem is that I only want to avoid this problem when the cause of the failure is that I'm online and not when there's is another cause. Second is that when the cycle time gets to long (>50ms) the CPU should go into STOP.


So I wrote a program for this but during testing (with PLCSIM) I've noticed that during the exceeding of the cycle time the CPU indeed stays into Run, but when I'd stop the loop (Cycle time is normal again) programs aren't processed anymore.
Anyone:
- has experience with similar problems or with using SFC43?
- might know better ways to solve this problem?
- knows why the CPU doesn't process anymore?
thx in advance
HG

 

[L D[AR2P#0.0]]

My experience with PLCSIM (V5.2) is that the timed interrupt stops working if you do a lot of files accesses (but OB1 always keeps going). The scan cycle time for PLCSIM is set to 20 seconds by default and overrides the h/w config setting for the CPU. This can be changed using the Execute option on PLCSIM.

As for preventing the timed interrupt fault whist monitoring, my only suggestion is to reduce the code executed in the timed interrupt (easier said than done of course).