PXI 6071 Counting problem

[EdV]

I am counting ttl level rising edges with gpctr_source0 using a PXI 6071. The edges look fine at 2V on the oscilloscope which is what I believe the 6071 triggers at. I am getting lots of extra counts. There is under shoot of 1V on the falling edge but that doesn't seem like anything that would cause a false trigger. Any suggestions appreciated.

[Filipe A.]

Hello;

You are getting extra counts due to the fact that 2V is withing the dead zone of the TTL levels. The TTL standard is 0-0.8V = low level and 2.8V-5V = high level. Any signal in between 0.8 and 2.8 can be interpreted either as low or high by the counter.

That is why you are getting the extra counters.

Hope this helps.
Filipe A.
Applications Engineer
National Instruments

[EdV]

I am counting edge transitions not levels. 2V is the transition for low to high in TTL.The signal I am looking at is 0 to 5V not 0 to 2V which what you may have interpeted my original query as indicating.

I am going to SW debounce the signal with a VI. I think that should do the trick.

Thanks much for your interest.

Ed Vogel