How can I use digital outputs to generate pulses as small as 200 microseconds?

[mattykEE]

I need to generate atleast 4 digital output pulses at varying frequencies and at varying pulse lengths (from 200us up to 100ms). I'm pretty sure this is posisble to do with counters but I was wondering if there is some way to do this with a general digital output since the usb daqs only come with 2 counters. I am looking to purchase a USB daq (possible the USB-6216 or something similar) and wanted wo make sure it could handle what I wanted it to do. From what I heard thesmallest general digital output pulse possible is 1 ms. is this true?

One of the ideas I had was to utilize a counter as a sort of clock output and then feed it to a counter input and count the rising edges. Then I could set the digital outputs to be on for the desired number of rising edges (through integer division of the count). Since I don't yet have the hardware and don't want to spend money on it if it won't work I wanted to see if anyone here has any information on how to handle this. 

I really appreciate any advice on this issue. Thank you,

-Matt

[John_P1]

Hi Matt,

Welcome to the NI forums!

On our boards that support Correlated Digital I/O, it is possible to use a counter to generate a clock signal, then update the Digital I/O based on that signal.  The following example should be a good starting point to show you how this could be achieved in LabVIEW:

NI-DAQmx: M Series Pulse Width Modulation (PWM)

However, the 621x boards do not support Correlated Digital I/O.  So, on the 621x board you are limited by the rate your loop can run in software (the Windows clock has a resolution of 1 ms so this is likely where that number originated). 

To implement the digital pulses on more than two lines, I would recommend looking into a device that supports Correlated Digital I/O (622x, 625x, 628x).  The entry level for USB is the 6221, which would give you 8 correlated digital lines with update rates of up to 1 MHz.

If you have any questions don't hesitate to post back.  Thanks for posting and have a great day!

-John