Basic Labview Programming Questions

[Greg McKaskle]

I think you are making progress. As with any language, you are starting to get into the details a bit.

Structures such as loops, cases, and sequence structures contain subdiagrams -- just like the top level diagram or the diagram in a subVI. The primary difference is that subdiagrams synchronize the inputs and outputs using tunnels and shift registers.

Some basic laws of LV execution.
When a diagram executes, all objects on the diagram execute once honoring dataflow between nodes. Breaking this down a bit, this means that no node can execute again until all other nodes on the same diagram have finished executing. It also means that no nodes will be skipped.

Structures are nodes which own one or more diagrams. Structures generally differ in how they schedule their subdiagram(s). Sequences execute them one after the other. A case structure executes just one of the subdiagrams. And the loops execute the diagram repeatedly, according the loop logic.

Data flow wires have a few laws too.
A wire has exactly one source and one or more data destinations. The job of the wire is to deliver the same value from the source to the destinations.

Getting to the point of your question, when a wire leaves a diagram, via a tunnel, sequence local, or shift register, the wire ends, and on the other side, well, that is another wire.

A node cannot begin executing until all of its inputs have arrived, and it cannot put data on a wire until it has finished executing.

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Since, a loop is a node, when it begins execution it latch data from the outside wires to the inside ones. When it finishes, the data on the inner wires will be copies to the outer downstream wires.

Sorry if this is abstract, but these are the LV language's grammatical rules. And grammatical language discussions tend to be abstract.

Greg McKaskle