Can the TTL inputs of my 6602 be damaged by low but negative voltages?

[Travis Mitchell]

I am interested in using the counters of my 6602 board to measure the frequency of a sine signal. I could convert the signal to a TTL compatible pulse signal, but was wondering whether I could simply hook up the signal without doing this. The input voltages would be low (<4V pk-pk), but I seem to recall that TTL inputs can be damaged if the voltage goes negative. Would it damage the board to try this?

[Arun_V]

Hello Travis,

National Instruments does not recommend giving an input voltage less that -0.3V. How much less can the board can take is another question and it might vary. I would not try any voltage less than -.3V

Arun V

[acanivell]

Hello there ... though this thread is quite old ...

I am doing the same, using a 6016 DAQ and a pulse generated through a schmitd trigger from a sinewave

I get a peak negative voltage of -0.3 V and it works fine and the limit in the NI6016 is 0V. In the 6602 it is -0.3V, so therfore you should not have much trouble.