When a DI change detection task runs, the first sample shows the DI state *after* the first detected change. There's not a clear way to know what the DI state was just *before* the first detected change, i.e. it's *initial* state.
This idea has some overlap with one found here, but this one isn't restricted to usage via DAQmx Events and an Event Structure. Forum discussions that prompted this suggestion can be seen here and here.
The proposal is to provide an addition to the API such that an app programmer can determine both initial state just before the first detected change and final state resulting from each detected change. The present API provides only the latter.
Full state knowledge before and after each change can be used to identify the changed lines. (Similarly, initial state and change knowledge could be used to identify post-change states.)
My preferred approach in the linked discussions is to expose the initial state through a queryable property node. The original poster preferred to have a distinct task type in which initial state would be the first returned sample. A couple good workarounds were proposed in those threads by a contributor from NI, but I continue to think direct API support would be appropriate.
-Kevin P
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