S7 with Cyclic Interrupt OB35

Hi to all,

I'm rewriting a project with a Siemens S7-315. I'm talking about a small machine with AS-i Master and about 96DI/96DO over AS-i bus. The program is built that all DI/DO's are stored in DB1.
PID 256 -> DBD56 is done in FB1
PID 260 -> DBD60 is done in FB99
PID 264 -> DBD64 is done in FB1

DBD76 -> PQD256 is done in FB99
DBD80 -> PQD260 is done in FB2
DBD84 -> PQD264 is done in FB2

FB1 & FB2 are called from OB1, FB99 is called from OB35. I know that this OB will interrupt the programs at a fixed interval.
In my best French I think that the comments of the original programmer warns us that there will be trouble when OB35 is not used or when all IO's are put together in FB99. I can't try however.
The IO's copied in FB99 are random and not for specific funtions.
Does anyone know what the average scan cycle is for reading the IO's in FB1 & FB2. Maybe there's another reason or benefit in using OB35 that I don't know about.

Help would be appriciated!
Gr.
Heino

Why not directly in OB35:
L PED260
T DB1.DBD56
etc.?

I think all 3 PED's (PID) can copy in OB35 from periphery to DB
and vice versa to PAD's without time problem if not under 10ms cycle have used for OB35 call. But I'm only beliving so..

Just a thought!

What about Data Consistency in 1. scan cycle, could that bee a problem?

Jesper.

Seppoalanen,
I'm guessing the same thing, problem is that i can't try directly on the machine

Jesper,
I have made a test application, until now there's no problem with data consistency.

Gr.
Heino

... in every application i've ever made, inputs are read at the start of ob1 and outputs written at the end of ob1 INTO/FROM I/Q CACHE HEAP ... reading of PI AREA mean that you just read memory already assigned before start of OB1 (communication with various unit is done 'in behind' and really vary from scan cycle anyway), CPU is doing that independently of any OB or FB unless you declare ... so i have to agree with seppoalanen

... where is no benefit of writing datablock in ob35 simply because ob1 should be called more often ... if you'll change any data in ob1 ... ob35 will surely have data not older than one scan length ... if you'll change data in ob35 then you can have different data in the start and end of processing !

imho it's wise to not work directly with outputs in ob35, inputs should no really matter ...

thanks guys!