CompactLogix - Could you please explain what a S:FS is,and what does it do in a rung

Baker in Virginia · Nov 29, 2019

Good Morning ,

Could you please explain to me what a S:FS is , what the purpose of it is and why would it be used in a rung.

Thanks so much.

mylespetro · Nov 29, 2019

It's a status bit from the processor that executes once during the first scan (FS) of the program, and then doesn't execute in subsequent scans. Can be used to initialize a program that has programming that may care about whether or not the PLC has been shut off, among many other things.

Baker in Virginia · Nov 29, 2019

Thanks

Geospark · Nov 29, 2019

Just to add...

mylespetro said:
It's a status bit from the processor that executes once during the first scan (FS) of the program, and then doesn't execute in subsequent scans. Can be used to initialize a program that has programming that may care about whether or not the PLC has been shut off, among many other things.

As Logix 5000 projects may contain multiple Programs within the default Main Task, or indeed multiple Tasks with multiple Programs, there may potentially be many Programs within a project. It is therefore important to be aware that each Program has its own First Scan Bit (S:FS) which will execute independently to the First Scan Bit (S:FS) in any or all other Programs within the project. That is, an observed First Scan Bit (S:FS) is not global to the project, even though its multiple instances are named identically.

Regards,
George

mylespetro · Dec 2, 2019

Geospark said:
Just to add...

As Logix 5000 projects may contain multiple Programs within the default Main Task, or indeed multiple Tasks with multiple Programs, there may potentially be many Programs within a project. It is therefore important to be aware that each Program has its own First Scan Bit (S:FS) which will execute independently to the First Scan Bit (S:FS) in any or all other Programs within the project. That is, an observed First Scan Bit (S:FS) is not global to the project, even though its multiple instances are named identically.

Regards,
George

Great to know, I guess I was thinking moreso the first scan of the processor even though I said program, so it's important to know that it's actually unique to each program. Thanks George!

CompactLogix - Could you please explain what a S:FS is,and what does it do in a rung

Baker in Virginia

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