The names "Source", "Gate", "Aux", "Out" do refer to specific signal types. The way these signal types map to actual connector pins is hardware-dependent, though there is a specific default pin that will be used if nothing else is specified. Certain counting modes (position encoder mode) will require physical wiring connections to default pins. Other modes will allow more flexible signal routing.
Yes, it is possible to "gate" the output of one counter with the output of another.
As a LV guy, I can't comment on the VB.net syntax. But in addition to configuring the signal routing, one must also configure the counter in question to "pay attention to" the gate signal. Under LV and DAQmx, this would be known as "Pause Triggering." Without setting up "Pause Triggering", the counter treats the signal at its gate as irrelevant. You can think of a Pause Trigger as a level-based Enable signal.
A "retriggerable" counter would use its gate signal differently. It would be edge-sensitive and wouldn't respond to a constant-high signal.
Sometimes it's not clear how to map DAQmx terminology down to the underlying counter hardware. Under traditional NI-DAQ, you basically were forced to understand how the counter hardware worked with "Source", "Gate", etc. signals. DAQmx largely removed that requirement. As a result, most simple operations and many intermediate ones are easier to setup, but other less common tasks can be a bit confusing. I've had trouble finding the correct property to set when trying to do period measurement with an external clock.
At the hw level, the Source increments the count register. The Gate is a control input, either a level-based Enable, an edge-based sampling clock, or an edge-based trigger. Aux is typically only used for position measurement. Out seems self-explanatory, though there are various non-default output modes that can prove handy at times.
Under DAQmx, the Source is defined differently for different counting modes. For edge counting, you wire in a signal identifier. For period measurement or pulse generation, it wants to use an internal clock. Similar for Gate. Sometimes you set it up as a pause trigger, sometimes as a sampling clock, sometimes as a digital start trigger.
Hope this helps some. Have fun with the 6602, it's a pretty nice piece of hw!
-Kevin P.
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