Step7: OB35 with 10ms cycle time

Hi all,

I have a little problem related OB35 with 10ms cycle time. I need to set one output ON every 30ms, i.e 10ms ON then 20ms OFF then 10ms ON etc.

I created a simple test program with empty OB1 and OB35 containing only this function. When monitoring with oscilloscope I could see that function itself works. However when I added this to project (i.e there are several calls in OB1) function behavior changed totally. I did some research and found out that this problem is related to process image someway, meaning that when output is set ON in OB35 process image is updated in next OB1 cycle.

How should I proceed with this one? For my understand is that I should somehow use peripheral addresses for this.

Yes, you must use peripherial addresses.
You have to use an intermediary binary address for the logic, i.e. M20.0, then copy the intermediary byte to the direct peripherial output byte, as the last thing in OB35:

L MB20
T PQBxx // must be PQ address !

JesperMP said:

Yes, you must use peripherial addresses.
You have to use an intermediary binary address for the logic, i.e. M20.0, then copy the intermediary byte to the direct peripherial output byte, as the last thing in OB35:

L MB20
T PQBxx // must be PQ address !

Click to expand...

To ensure you don't damage other signals I would do something like this

L QBx
T MB20

manipulate bit in MB20 and then

L MB20
T QBx
T PQBx

Very valid points, Peter.
To do as you describe it is a MUST.

No need to use MB, process Q bits as normal and then execute

L QB x
T PQB x

to update the outputs immediately.

Thanks to all. Now this is working also with whole project.