Hi experts,

Would somebody be able to explain me the following result:

A TRUE

O

A (FALSE)

A FALSE

= RESULT

The simulators shows the result is equal to TRUE but if i execute in a paper line by line (without using algebra and different priorities it would seem that:

A TRUE                     RLO=1

O                                RLO=1

A (FALSE)                 RLO=0 (TRUE AND FALSE)

A FALSE

= RESULT

Can somebody please explain me what I am doing wrong?

Thanks

Dear Yu-wen,

Thanks for your quick answer. Yes when I looked it in ladder it looked easier. My issue is that the site code that I was trying to modify is a lot longer and so very difficult to represent it in Ladder but I have achieved to reduce it to my original question:

A TRUE

O

A (FALSE)

A FALSE

= RESULT

The reason for asking is that I wanted to find a algorithm to execute this STL code in my head. I always understood that Siemens was executing line by line and if there was brackets then  S7 was saving the RLO in a stack. Sadly, in the case above this execution line by line does not seem to work.

piteu

A TRUE

O

A (FALSE)

A FALSE

= RESULT

The reason for asking is that I wanted to find a algorithm to execute this STL code in my head. I always understood that Siemens was executing line by line and if there was brackets then  S7 was saving the RLO in a stack. Sadly, in the case above this execution line by line does not seem to work.

 It's not quite how you are thinking it is... maybe this screen capture from Step7 STL programming manual helps you to understand how it works. You can find more information by searching "Nesting".

Hello piteu,

it is better to understand STL when brackets are used (for readability).Then your code looks like this (see also LAD-code posted by Yu-wen Tang and logically because no statement for "O"):

(

A TRUE

)

O

(

A (FALSE)

A FALSE

)

= RESULT

In one line: (TRUE) or (FALSE and FALSE) = TRUE.

Regards,

Frink 

Hi all,

Thank so much for all your help.

Thank you