Triggering and acquisition happen on the device in hardware. Latency and timing consistency will be fine for analog acquisition.
Buffering is typically split. The hardware device has a small-ish buffer while the task buffer that resides on the PC is typically larger. The hardware buffer gives the DAQmx driver a little time to move samples from the device to the task buffer on the PC. Then your app needs to retrieve data from the task buffer fast enough that it "keeps up with" the acquisition.
I typically define task buffers that are 1-5 seconds long and read 1/10 sec worth of samples per call to DAQmx Read. It works reliably across many devices, many sample rates, and apps that may run for hours (or even days).
All that said, those cheaper USB devices do *not* support hardware-based sampling of digital signals. You'll be better off wiring the digital signal into another analog channel that you include in your task. Then you can search through the data for the digital transition as you read it from your task.
-Kevin P
ALERT! LabVIEW's subscription-only policy came to an end (finally!). Unfortunately, pricing favors the captured and committed over new adopters -- so tread carefully.
