9401 buffered digital output sample clock source

[JPP]

Hi, I wish to generate a pulse train with a defined number of pulses, at defined frequency. I am using a NI9401 module in slot 3 of a CompactDAQ chassis so that I can write the required pulse train to the 2047 sample buffer. The problem I have is I am unable to select any clock source slower than the 100kHz timebase, and this means the buffer can underflow very easily. I would like to use a clock source of 4kHz, but cannot find how to do it. If I want to generate a clock source from one of the counters, then I must have the 9401 in slots 6 or 7 which then do not allow buffered digital waveform generation..

[S_Hong · Accepted solution]

Hi JPP,

You can internally access the counters even though the modules are connected in slot 1-4 of the cDAQ chassis. Note that slot 6 & 7 are only necessary if you need external access to the counters as in buffered counter tasks, frequency/period measurements, etc.... Since in your application, all you need is to generate a continuous pulse train and access its output internally to clock your correlated digital output, this should not pose any problems with your DIO module in slot 4. Please have a look at the following link for more information.

Using Internal Counters on a NI cDAQ-9172 as a Sample Clock for Other Tasks

http://digital.ni.com/public.nsf/allkb/EEB574335BA0B4EB862572060055E9DD?OpenDocument 

I would also like to refer you to an example on our site which shows you how to use the counter to clock your correlated digital I/O. I hope this helps.

NI-DAQmx: Correlated Digital I/O with NI CompactDAQ and LabVIEW

http://zone.ni.com/devzone/cda/epd/p/id/5256

[JPP]

Thanks for that. Exactly what was needed.