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Can I Change the Memory Allocated to Specific Channels Using NI's Digital Waveform Generator/Analyzer?

Primary Software: Driver Software>>NI-HSDIO
Primary Software Version: 1.3
Primary Software Fixed Version: N/A
Secondary Software: N/A

Problem: I am not using all the digital lines on my Digital Waveform Generator/Analyzer (NI 654x, 655x, 656x). Can I optimize all the onboard memory so it is used only by the channels that I will be accessing?

Solution:

Waveform Generation

Changing the per channel memory for generation sessions is not possible with any of the NI Digital Waveform Generator/Analyzer modules.

Waveform Acquisition

Yes, NI-HSDIO 1.3 or later allows the user to allocate all the onboard memory to three different channel widths, 1 byte (8 channels), 2 bytes (16 channels), or 4 bytes (32 channels). This functionality is accomplished using the 'data width' property shown in Figure 1.




Figure 1



The 'data width' property can make your memory usage more efficient if you are not using all of the channels on your device. Let’s say that you have a NI 6542 that has 32 channels, but you are only acquiring data on channels 0-15. Without the data width property, the memory that is reserved for channels 16-31 would be filled with 0, and half of your memory would be wasted. With NI-HSDIO 1.3 or later, if you change your data width to 2 bytes (16 channels), you can now fill the per channel memory with double the number of samples.

Different data widths require different functions in either LabVIEW or C. In Figure 2 below you can see the acceptable functions to use when choosing various data widths. Keep in mind that different devices will have different native data widths, so you may need to change the data type of your read, fetch, or write function if you change to a different device. The 'Single Record' designation is not relevant in this case. The multi-record functions may be used, but they too must use the correct data type.

The LabVIEW Digital Waveform Datatype shown in Figure 3 may be used for all data widths. For more information about using the 'data width' property or other NI-HSDIO programming questions please refer to the NI Digital Waveform Generator/Analyzer Help document in the Related Links section.




Figure 2






Figure 3

Related Links: NI Digital Waveform Generator/Analyzer Help
NI-HSDIO Download KnowledgeBase 454AKQJQ: HSDIO Data Width and Memory Allocation


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Report Date: 04/29/2005
Last Updated: 03/23/2007
Document ID: 3KSDEV0M

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