Hello.

I need help to read the cycle time of previous OB1 scan on S7-300 PLC. Does anyone know which instruction I can use.

Thank you.

Hello,

You can use the variable "OB1_PREV_CYCLE"

Best regards,

Wizard

Hello Kiiaza;

The general way of reading the runtime of OB1 is to read the value of local data OB1_Prev_Cycle. See the screenshot below, from the System and Standard functions manual.

Of course, since this is local data, you must access it inside OB1, then send it to a global variable or DB INT variable.

Hope this helps,

Daniel Chartier

Hello guys,

Thanks for the quick support.

I think that variable should be able to work for me. I, however, have one more question. How do I bring that variable into my program? When I use the Load instruction in STL, it doesn't seem to work. I try to use it on the move block, it still shows red.

Thanks again.

Hello Kiiza,

Like DChartier already mentioned, you can only use it in OB1

Please tell us which software you are using?

Best regards,

Wizard

Hello,

My problem was, I could see the variable being used. But I did not know how to declare the variable within OB1. I saw an example where those variables are declared in the TEMP are of OB1. I tried to use the same. I get strange values when I monitor the same variables with PLCSIM. I am hoping when I connect to a physical PLC I will get actual values.

Thank you.

Hello Kiiza;

Whenever you test a program using PLCSim, you must always keep in mind that you are using a simulated CPU, there are functional differences between the simulation and real hardware.

Here is a FAQ that discusses these differences. Amongst other points it states that PLCSim does not handle time values as in a real PLC, which could explain your results:

https://support.industry.siemens.com/cs/us/en/view/11610958

Hope this helps,

Daniel Chartier