period changing of cyclic OB (OB30-38)

[jormaga]

Hi!

I was wondering if it's possible to change the period of a cyclic OB (OB30-38) with a function (SFC or whatever).

Thanks!

Regards,

Jorge

 

[TheStarr]

Are you using an S7-400 PLC?

 

[jormaga]

It's a 315-2dp plc...

 

[L D[AR2P#0.0]]

No.

Why ?

 

[TheStarr]

Not to familiar with S7, but it looks like you can delay or disable for a determined amount of time using an SFC.

This manual looks like a "must have" for programming S7. Lots of good info.

http://dce.felk.cvut.cz/rs/plcs7315/manualy/sfc_e.pdf

 

[rdrast]

Do you mean to change the cyclic scan time? or a periodic task scan time?

For a periodic task, one way is to make it run at the fastest rate you need, maintain one or more counters, and then call 'slower' logic ever couple of passes through it.

This only works if you have an integral relationship to your scan needs though.