How do I get started with PXI timing?

[mahill]

I'm working in a lab that is trying to start to use a National Instruments PXI/VXI hybrid system.  I currently know very little about timing and triggering.  Basically all I know is that the timers we are using (PXI-6653) generate a square wave at 10 MHz and I can route it to the CLK10_in.  I'm able to confirm that the clock is being routed there by using some of the example VIs and using a scope to see that the square wave is being outputted through the BNC connector on the back.  I can see it's not the regular PXI 10 MHz reference clock because there is a difference in 10 MHz signals between before I hit the "GO" button on the routing VI and after I hit the "GO" button.  So all in all, I can confirm I'm getting the 10 MHz signal routed to the CLK10 backplane signal.

However, my main question is how I can use that CLK10 signal on my DAQ cards?  We are using PXI-4462 and PXI-6123 cards.  I'm trying to use some of the example VIs given with NI-DAQmx.  Is the "onboardclock" a timer that's on the DAQ card itsself?  What about this sampleclock?

I've read through the examples and tutorials on the NI website, and they aren't very "newbie-friendly". 

Thanks,

Michael 

[RT4CY]

Hello Michael,

Thanks for posting on the forums!  What you are trying to do is called reference clock synchronization.  This is also referred to as Phase Lock Looping (PLL) to a reference clock.  You will access this reference clock with a DAQmx property node as shown below.



Your PXI-4462 is a DSA device.  This needs to be the Master device.  Take a look at the Synchronization examples that ship with LabVIEW.  Launch the NI Example Finder by going to Help»Find Examples.  Browse by task to Hardware Input and Output»DAQmx»Synchronization»Multi-Device.  The image above comes straight from the Multi-Device Sync-AI and AO-Shared Timebase & Trig-DSA.vi  example.  You can modify this example to suit your application.  But remember, the DSA device needs to be the master.

You may be wondering what the Sync Pulse is for.  In addition the the NI Example Finder, the NI-DAQmx Help is a great resource.  Do a search for Sync Pulse, and you will find quite a bit of information about it as well as other useful things to know and consider with DSA synchronization.

Message Edited by RT4CY on 10-25-2008 03:06 PM

[mahill]

Rod,

Thanks for your reply.  For some reason, I am having ussues setting the PXI_Clk10 signal with my 6123 cards.  It says that the specified property is not supported for my device.

Michael

[RT4CY]

Hey Michael,

Please accept my apologies, according to this KB article your device cannot use the 10 MHz PXI clock.  The 6123 device falls under our S-series family.  Only a couple S-series device can use this backplane clock.  You will need to synchronize the devices by sharing the timebase from the DSA.  Sorry about the confusion!