USB 6009 Digital Input Sample Clock

[ssingh1]

Can any one tell me the Sample Clock frequecy (dt) of a single channel Digital Input of USB6009 when we Read data using Digital Waveform 1 Channel N Sample mode?

In the digital waveform received the dt parameter is 0, however all the samples are read at the end of complete acquisition?

Is this hardware timed or Software Timed Input, as the read command is given only once per acquisition and all the samples are received automatically?

Can this waveform be used for comparison of data received from the Analog Input side?

Please reply.

[Dennis_Knutson]

As you should know from reading the manual for the 6009, the digital I/O is software timed only. You can only take a single sample at a time - not a waveform. The actual time between samples is going to be dependent on your pc, os, etc and will be subject to quite a bit of jitter.

[ssingh1]

Yes Dennis, thanks for your quick reply.

I did read the manual. But I am confused because I can acquire complete Digital Waveform (containing n number of samples) at a time and not a single sample.

Is this a driver feature?

[Dennis_Knutson]

Or perhaps you are getting an error and ignoring it? No idea. As far as I know, specifying anything other than  1Sample/On Demand timing will result in an error.

[ssingh1]

No certainly there is no error and i get N number of samples in one go without any error.I have not configured a sample clock (as it gives an error) although.

The sampling seems to be around 1000 samples per second as I can make out from the time taken (about 1000ms) for taking a 1000 samples. The thing is that I get 0 in dt parameter of waveform and cannot makeout the exact timing.

I will post the VI which I am using along with the sampled data when I reach office tomorrow.

[ssingh1]

Here is the VI used for testing purpose.

[ssingh1]

Any Replies Please.

[Dennis_Knutson]

Interesting. I've never tried the NSamp option. With static digital, I've just placed the read in a loop. Perhaps the driver is doing something similar but since it is software timed, it will not return a dt value.

[MarkGrot]

Dennis is correct.  The underlying implementation is not hardware timed.  You should not attempt to correlate the data to analog input samples, because there is no way for you to determine dt.  The implementation is essentially the same as you calling read 1 sample in a loop.

[ssingh1]

Thanks Mark & Dennis for your valuable inputs.

One Last question, can we take this digital pulse input from the counter input (pfi) of USB6009 and co-relate with Analog Input (in any way), as it may be hardware timed?

Otherwise , we will have to use other hardware timed board for our purpose.