Trouble cascading counters in DAQ MX

[CoastalMaineBird]

Using LV 8.2 and DAQ MX, I'm trying to use two counters cascaded as a single counter.

First I CREATE CHANNEL (CI Count Edges, Dev1/Ctr0); I set that channel's CI.COUNTEDGES.TERM property to Dev1/10MHzRefClock. I start that task.

Then I CREATE CHANNEL (CI Count Edges, Dev1/Ctr1); I set that channel's CI.COUNTEDGES.TERM property to Dev1/Ctr0InternalOutput. I start that task.

So, when I want to read them, I call DAQmx READ for task one, and DAQmx READ for task two.

I then JOIN NUMBERS to combine the HI and LO parts into a single U64.

That all seems to work, except it seems vulnerable to the old 12:59 problem.

(If a clock is sitting at time 12:59, and you read the hi part and low part SEPARATELY, then it just might tick over in between your reads, and you get either 12:00 or 1:59, depending on which side you read first).

I MUST use two tasks, it seems, because the rules say I cannot use two counters on one task.

The HELP for CREATE VIRTUAL CHANNEL, CI CNT EDGES says: To read from multiple counters simultaneously, use a separate task for each counter.

But how can I READ two tasks simultaneously?

[Elijah_K]

CoastalMaineBird,

Are you trying to measure continuously buffered frequency using two counters?  LabVIEW ships with a number of examples of how to properly implement this and they can be found in the example finder: Help >> Find Example.

Dig down in the folder hierarchy to Hardware Input and Output >> DAQmx >> Counter Measurements >> Digital Frequency.  There you'll find a number of detailed examples that use two counters to measure a frequency.

Let me know if this isn't what you need or if you still have any questions.

[CoastalMaineBird]

Are you trying to measure continuously buffered frequency using two counters?

No.

I am trying to make a stopwatch for timing various parts of my (RT) program.

I want to set up a task, and call my timer VI's START function.

Some time later, I want to call its SAMPLE function, and have it return to me the number of clock ticks (or uSec) between the START and the SAMPLE calls.

I want a wide dynamic range, so I can use it on anything from uSec to sec, without having to guess.

I have it working, except that it seems like it would be susceptible to the 12:59 problem.

The example you cite, as far as I can tell, only works with frequency measurements, because the "high frequency with two counters" option is only available with the CI FREQ variants.

I am using the COUNT EDGES variant, and I see no such option available.

[CoastalMaineBird]

Actually, I just now found the PRESCALER property. With a 10-MHz clock and a prescaler of 8 on a 24-bit counter, that gives me a resolution of 800 nSec, and a range of 13+ seconds. That's good enough for me.

Still, I'm curious as to how to implement the help's suggestion (to read two counters simultaneously, use separate tasks).