Distributed Control & Automation Framework (DCAF)

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Where does the Scan Engine Module Get It's Timing Source?

Does the DCAF scan engine module use the scan period provided in the DCAF configuration manager or the scan period configured in the properties menu of the CRIO?

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There are potentially two timing sources involved here.  One is the source of when values are transferred between scan engine and the hardware, and when values are transferred between scan engine and the DCAF engine.

The data values available to read from scan engine are updated based on the scan period configured in the RIO properties.

The timing that DCAF uses to read them can be synchronized to the scan engine.  The setting for this is located in the configuration page for an engine in the DCAF editor.  The selection you're looking for if you want DCAF and Scan Engine to work at the same base rate is the 'Synchronize to Scan Engine' option for the Timing Source Type.

If you have a different value for timing source type, then scan engine and the dcaf engine will not be synchronized and you might get data sets that come from different scans of the hardware.


Matt Pollock
National Instruments
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One other note, the DCAF Scan Engine plugin module requires a user to specify the Scan Engine period. The module will programmatically set the scan engine rate at runtime to the specified value. This was done to reduce the dependency on specifying settings in the LV project.

So to set a scan rate and synchronize the engine to that rate:

  • Add a Scan Engine module to an engine.
  • Specify the rate/period on the Scan Engine module's configuration page.
  • Select 'Synchronize to Scan Engine' as the Standard Engine's timing source

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Thanks for the responses.

I think that answers my questions.

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