Siemens S7 TIA Portal - FC / FB

[kreskin]

That's ok as the global DB references are not in the FC itself.

Yes, got that, thanks LD

 

[drbitboy]

So passing this information to the FC/FB input parameter would be copied [Note 1], whereas alternatively using the InOut data type means that the FLC fluctuations will still be captured during [Note 2] manipulation within the FC/FB's logic?

Yes.

Note 1: with the values in place at the time of the FC/FB call, and I don't know for sure if it could happen, but in theory an update (see Note 2) could come in and stir the pot during the copy.

Note 2: "during" assumes updates are asynchronous with, and/or higher priority than, program scan.

 

[drbitboy]

using the InOut data type means that the FLC fluctuations will still be captured during manipulation within the FC/FB's logic?

That said, the core and design assumption of a digital PLC is that its scan time is, in effect, infinitely fast, i.e. the code being executed behaves, for all practical purposes, the same as analog logic. I heard that the original PLC spec was something like 100ms scan times because the typical relays implementing the logic they were replacing changed state no faster than that anyway.

If you are applying PLCs to a process where a 1-100ms scan cycle is not fast enough, understanding Input, Output, and InOut is the least of your worries.

 

[kreskin]

Yes.

Note 1: with the values in place at the time of the FC/FB call, and I don't know for sure if it could happen, but in theory an update (see Note 2) could come in and stir the pot during the copy.

Note 2: "during" assumes updates are asynchronous with, and/or higher priority than, program scan.

Ok, get it. Thank you.