How to creat N number of pulses precisely with PCTIO-10

[chen@rowland.org]

I need to send out N number of 1us pulses precisely with PCTIO-10. This is what I try to do: I use ctr1 to create 1us pulses. The output of Ctr-1 is counted by Ctr2 and the output of Ctr-2 in turn gates Ctr1. I use NI-DAQ CTR_PULSE function. I load N number of counts and Ctr2 enables Ctr-1, when ctr2 reaches the preloaded counts it toggles the output (pulse width =0) and holds ctr1. This suppose to do it. But the result is bad. It only works if the counting time of CTR-2 is greater than 180us, yet the PCTIO-10 has a time resolution of 140ns.

Any ideas on what is going on or alternative methods?

[Matt_R]

There is an example that ships with LabVIEW that will generate a set number of pulses with a user-defined frequency and duty cycle. This example uses both counters, and can be found by selecting "Search Examples" from the LabVIEW splash screen. From the help window that comes up select "I/O Interfaces -> Data Acquisition -> Counters -> Finite Pulse Train" The program you want is titled "Finite Pulse Train" under the NI-TIO based devices.

Documentation on this example is available by opening up the VI Properties window from the File menu, and going to the documentation category. Good luck!

[chen@rowland.org]

I think instead of using the zero pulse width to toggle at precise time the output of counter 2 which in turn provides a gate signal to the first counter, I should use a finit pulse width as a gate signal to avoid the problem I ran into. As long as both counters use the same internal clock source, one should get precise results.

[Erin_B.]

Since the PC-TIO-10 is not based on the NI-TIO ASIC, I would not recommend using the NI-TIO examples. The TIO-10's counter VIs are incompatible with the VIs for the NI-TIO ASIC. The examples that you need to look at are for AM9513-based devices.

Regards,
Erin

[shawn]

The PC-TIO-10 uses source frequencys of 1 MHz, except for Source 5 and Source 10, which use 5 MHz. In order to generate 1us pulses, you may need to use the 5 MHz source. Unfortunetly, since the PC-TIO-10 is an older counter board, there are not very many examples for how to program it using NI-DAQ.
Also, you should be able to get a finite pulse train by using only 2 counters. You should Call CTR_Config for both counters, then call CTR_Rate and CTR_Square for the counter to generate the pulse train. You may want to check the parameters returned by CTR_Rate to make sure that they will give you the correct frequency and duty cycle. You should then call CTR_Pulse for the counter that will gate the pulse generating counter.
I would suggest starting the program by generatin
g a continous pulse train, making sure that works, and then adding the second counter to only generate N pulses.

I hope this helps. If you have further questions, you may want to refer to the PC-TIO-10 User Manual and look at the Specifications for the AM9513 chip.

Also, the following Knowledgebase talks about the maximum frequency possible for the PC-TIO-10:

http://digital.ni.com/public.nsf/3efedde4322fef19862567740067f3cc/48a4924ba92f431c8625686900773e96?OpenDocument

[chen@rowland.org]

This is precisely what I did and described. But it doesn't work. Why?

[shawn]

Good Quesion. If you try to generate a continuous pulse train (not to generate N pulses) using just one counter, does that work? You should be able to start by generating a continous pulse train and seeing if that works. If it does, then you should be able to just add the second counter to generate a single pulse, and connect that counter's output to the original counter gate.

I hope this helps. I don't check the developer zone too often, so communication this way isn't the best method for me. If you want to talk about this further, it would probably be best to go to www.ni.com/ask and submit a question to National Instruments, and ask that the question be directed to me, Shawn Walpole.
Also, I would strongly suggest using a newer counter board wh
ich not only has better specs and accuracy, but also more examples. The PC-TIO-10 is an older product that we don't have too many examples for. It will work to generate a finite pulse train, but we don't have any examples of how to do it in C.