Acquiring More Records Than Fit in Digitizer Memory

NI High-Speed Digitizers Help (NI-SCOPE)

Edition Date: January 2017

Part Number: 370592AB-01

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During typical multirecord operation, each buffer in memory must be large enough to contain all the pretrigger and posttrigger samples. If you request 1,000 points with Configure Horizontal Timing, each record in memory must be at least 1,000 points; otherwise NI-SCOPE returns an error. Typically, all the records are required to fit in memory, so you can wait until the entire acquisition is finished before fetching anything.

However, in certain cases, you may want to acquire more records than would fit in the onboard memory. In this situation, the records in memory are also circular. That means if you configure four records and only three fit in memory, the fourth record overwrites the first record. Ideally, you have time to fetch the first record to the host computer memory before it is overwritten.

To fetch more records than fit in memory, set the Boolean attribute Enable More Records Than Memory to TRUE and configure the desired number of records with the Configure Horizontal Timing function. You must fetch the records individually as described in Fetching Triggered Records while other Records are Being Acquired. If the record you are attempting to fetch has been overwritten, NI-SCOPE returns an error.

Caution   The total number of records that you can acquire is limited. Each record requires up to 64 bytes of page-locked memory. Windows 2000 can crash without warning if too much memory is page-locked at any given time. The actual amount of page-locked memory depends on the amount of physical memory and the number of other devices being used in your host computer. You can configure as many records as you need, but save your work first.

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