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Lowest possible digital input latency on FIOx


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#1 chuckb

chuckb
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Posted 28 December 2012 - 12:09 PM

I've read though various other postings on latency of AIN, DO, etc... I have an application where I need to detect the change of a single digital input as fast as possible, even if it means totally gross inefficiencies :rolleyes: . Some options that occur to me: 1) Stream channel 193 at 50kHz with only 1 sample per packet, and LJ_swNONE retrieval. Yes I know the User's Guide warns about potential Host PC processing limitations, but what are today's limitations on ever-faster machines? 2) Submit multiple BitStateRead commands in Feedback function. How does that compare to 50kHz streaming? If I were to do that, what kind of idle gap time would I suffer between between Feedback calls as compared with the regularity of Streaming? I am concerned about worst-case here. Are there any other best-known methods for minimizing DI latency? Thanks!

#2 LabJack Support

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Posted 03 January 2013 - 01:36 PM

With command/response feedback functions, the gap time is going to line up with the times from Section 3.1:

http://labjack.com/s...users-guide/3.1

So you could have a typical gap time of 600us, but sometimes you might have a much higher gap if Windows decides to do some other higher priority task.

As for stream with a single scan per packet and read, it might do a little better. I tested with one of our low-latency stream examples for LabVIEW and was able to go as fast as 3000 scans/second. That was actually with a 4-channel scan, so might be able to do even better with a 1-channel scan.


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