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PFI pin unable to read TTL signal from GPS unit


Hey Everyone, 


I have a GPS unit that sends a PPS (Pulse Per Second) to NI 6229. The PPS signal is a TTL signal of 3.3V. The PPS signal is sent to NI 6229 at 1Hz. The issue is that the NI cannot seem to read the PPS signal. I have looked at the oscilloscope, and I can see the signal. I don't know what's going on. Please help!!  Just an assumption, could the reason why NI card cannot read the signal is due to the speed of the TTL signal. 

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How are you trying to read it?  What is the pulsewidth of the signal?


Open up MAX, open a test panel for your device, choose counter i/o edge counting mode.  If the pulsewidth is very small, this will be much more effective than polling the signal via standard digital input.



-Kevin P

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Thank you. I just realized that it was a timing issue. The GPS unit was sending PPS signal in microsecond while i was reading in millisecond. I had to convert the PPS Signal to millisecond. 


Thank you 

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