6110 external master clock

[John_P1]

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@wm John Weeks wrote:

So I need to create an analog input scan task (for instance) and use that task when setting the master timebase source and rate? Other tasks won't be bothered by this as long as they don't contradict the setting? Or do other tasks also have to set the same master timebase properties?

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All tasks using the master timebase on a board have to have the same master timebase settings.  By default this is any task using an internally derived clock or timebase.

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My customer wants to sync his Acqiris ultra-high-speed DAQ device with his 6110. The Acqiris device produces an appropriate signal for the purpose, but doesn't produce the appropriate signal for an external sample clock. If that had been acceptable, I would have solved this long ago!

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So I'm assuming the Acqiris produces a higher frequency clock that you would like to divide down to give the AI Sample Clock.  This is what the AI Sample Clock Timebase is used for, which is what Dan was suggesting that you use.  You can route it on any of the PFI lines.  It is really very similar to the Master Timebase but it is unique for AI tasks.  The diagram I posted earlier gives a good visualization of the possible sources and derivations of the clock.

I hope this helps, please don't hesitate to let us know if you run into any issues!

Best Regards,

[Mcdan]

So I need to create an analog input scan task (for instance) and use that task when setting the master timebase source and rate? Other tasks won't be bothered by this as long as they don't contradict the setting? Or do other tasks also have to set the same master timebase properties?

The problem here as that by default tasks will attempt to route the internal 20 MHz clock to the master timebase source.  This will by default conflict with the task which has specified different routing.  In short, the issue here is that tasks do not communicate with each other, so one task is unaware that a different task has specified different settings.  In this case, all tasks would need to explicitly make the timebase source and rate settings.

My customer wants to sync his Acqiris ultra-high-speed DAQ device with his 6110. The Acqiris device produces an appropriate signal for the purpose, but doesn't produce the appropriate signal for an external sample clock. If that had been acceptable, I would have solved this long ago!

If I understand you correctly, the Acqiris device exports a high frequency clock that you wish to divide down to use as a sample clock for your 6110.  What I have been trying to point out is that there are two ways to do this.  One, would be to connect this signal to RTSI7 and use this as your master timebase source.  As discussed above, this would require all tasks to specify this.  The other option would be to use this signal directly as a timebase for various tasks.  For instance, you can use an ai timebase which is not derived from the master timebase at all.  To do this, you would use the DAQmxSetSampClkTimebaseSrc and DAQmxSetSampClkTimebaseRate methods.  In this case, AI would use the external signal as it's sample clock timebase, but other tasks would still default using the default master timebase as their timebase.  (This is different from actually using the signal as a sample clock.  The sample clock timebase is a signal which will get divided down to create the sample clock).  Which method you should use really depends on whether you need all of the tasks running on your 6110 to use the same timebase.  If yes, then the the best way to go would be to get the signal from your Acqiris device to your 6110's RTSI7, and to use this as the source for your master timebase.  If you are only needing to synchronize one or two subsystems to the Acqiris device, then it may be easier set the subsystem specific timebase (ie... ai/SampleClockTimebase which the timebase that your AI sample clock would be derived from).  I was recommending this method as you'd mentioned that RTSI was not an easy option for you.

Apologies if I am not understanding what you need to do.

Dan

[WM_John_Weeks]

Dawn breaks over marble head...

Dan and John, I finally caught what you were saying about the AI timebase input. That might be a better solution (that is, less complicated solution). I will ask my customer.

Thanks!

[src42]

What are the signal requirements for a 20MHz master timebase clock input to RTSI7? The signal does NOT come from another NI card on the RTSI bus. I presently have a 0-2V 20MHz square wave with edge transition times less than 5ns. Is this signal sufficient?

[EEsRULEtheWORLD]

Hi src42,

If you are also using the 6110, which is an S series card, you would want to refer to the S series manual.  In this manual, you'll find the timing requirements for the Master Timebase on page 52.  If your signal fits these requirements, then you will be able to use it as the Master Timebase.

[John_P1]

While the manual states the timing requirements, it does not explicitly call out (in the Master Timebase section) that the digital lines use 5V TTL logic levels.  The 0-2V signal does not meet this specification (V_hi for the output should be at least 2.4 V).

Best Regards,

[src42]

The Mastertimebase signal is introduced to the PCI-6110 at RTSI7, with the source being external (not another NI card). Is it necessary or desirable to add to the configuration a RTSI cable as another device?

[Mcdan]

src42,

Adding a RTSI cable in Max, and then adding your device to that cable will allow DAQmx to automatically make routes between different devices on that cable, or allow you to specifically reserve lines on the RTSI bus (basically telling DAQmx not to use those lines when making routes).  This is very handy if you have multiple DAQmx supported devices attached to the cable, or have need to prevent DAQmx from routing through a particular RTSI line.  However, it is not required that you add the RTSI cable as a device.

Dan