I have an application where I need to count digital pulses, but the two counters on my PCI-6221 are already used for something else. I thought an efficient way to do this would be to use a VI similar to the Read Dig Chan-Change Detection.vi shipping example and simply keep track of how many samples were read. The problem I encountered was that the DAQmx Read VI only executes after a multiple of 4 changes.
To see what I'm talking about, add an indicator to the loop iteration terminal in the example and toggle the Rising/Falling Edge Lines. After 4 changes have occured, the loop will run and read the number of samples selected in the Samples Per Read control. If the Samples Per Read is set to 1, the loop will execute 4 times each time the number of changes is a multiple of 4; if it is set to 4, the loop will execute once each time the number of changes is a multiple of 4; if it is set to 3, the loop will execute once after 4 changes, once after 8 changes, and twice after 12 changes.
Is there anything I can do to find out how many changes have occurred in a multiple of 1 or 2? I've tried using digital change detection with the Register For Events node and using digital change detection as a timing source for a timed loop, but I would end up missing counts. (The pulses can be as short as 6ms and I'm running a lot of other stuff at the same time.) I was hoping that by doing a continous read, I could take advantage of the buffer so I didn't miss counts.
