Good morning Andronicus,
Thanks for contacting National Instruments with your issue, we'll try our best to resolve it for you as quickly and efficiently as possible.
Unfortunately, there is no easy way to do what you're trying to accomplish with simply a Scope alone. The trigger input and PFI lines have no buffer and are only capable of looking for a single edge, and the standard CH0 and CH1 inputs strictly represent signals in analog.
So your current approach may be best, of using the Fetch Forever to acquire the signal into a prebuffer and then analyzing it and sending a software trigger. So the best you can do in terms of response will be software-time, which is not ideal. There is also the very tricky matter of interpreting that analog signal as a digital signal. You'd have to know the clock rate of the incoming pattern and then also the phase in order to correctly assess the incoming pattern. No easy task, and certainly nothing that would be super reliable or recommended.
Your best bet would be to purchase one of our HSDIO cards, such as the PCI-653x that inherently does pattern triggering in the hardware domain, and then route the start trigger (i.e. when the pattern has been matched) via a RTSI cable to the Scope card which can then simply use the digital edge trigger to begin it's acquisition. This will be far more robust, easier to code and have a much quicker response time.
Best of luck with your project.
Sincerely,
Minh Tran
Applications Engineering
National Instruments
