Arbitrary Waveform Output Mode

For the PXIe-5433, arbitrary waveform output mode generates waveforms from user-created or user-provided waveform arrays of numeric data.

The waveform arrays are downloaded to the onboard memory on the instrument. Arbitrary waveform output mode also uses memory to store the instructions on generating waveform sequences in the waveform memory.

Note You cannot use the lookup memory in arbitrary waveform output mode.

Marker Output Signal

NI signal generators can generate markers at specific points within a waveform. A marker is a digital pulse that can be used as a trigger to control the timing of other devices in your application. You can route this signal to connectors on the PXIe-5433 front panel or to PXI trigger lines. You can place a marker in every sequence segment.

You can specify a marker by giving an offset count, in number of samples, from the start of the waveform buffer for each segment. If the waveform loops multiple times in a segment, the marker generates each time the waveform loops at the configured sample position.

If you need to generate a marker only once in a segment in which the waveform loops a number of times, break the segment up into multiple segments. For example, if you need to generate a marker on only the first iteration of a sine waveform that loops 100 times, create a segment that loops only once and generates the sine waveform with the marker at a specific sample position. Create a second segment that generates the sine waveform with no marker and loops 99 times.

This technique can be used in different combinations of segments to generate one marker every 10 of the sine waveform by creating a segment containing a marker and one loop followed by a segment with no markers that loops nine times. Repeat these two segments for as long as you need to repeat the cycle.

Minimum Waveform Size and Quantum

The memory architecture of the NI signal generators imposes certain requirements on the waveform size and quantum. If these requirements are not met, NI-FGEN returns an error. The specific values for minimum waveform size and quantum depend on the specific NI signal generator.

Note Refer to PXIe-5433 Specifications for minimum waveform size and quantum values.

Minimum Waveform Size

Every waveform downloaded to the instrument memory must be at least a minimum size in terms of the number of samples.

Quantum

The size in samples of the waveform downloaded to the instrument memory must be an integer multiple of a certain number or quantum.

For example, if the minimum waveform size for a particular signal generator is 256 samples, the quantum is eight samples, and you request to load a waveform of 255 samples, NI-FGEN returns an error because the waveform size is too small. If you request to load a waveform of 257 samples, NI-FGEN also returns an error because even though the size is larger than the minimum waveform size, the waveform is not an integer multiple of the quantum size (8).

Waveform sizes that meet the restrictions for this example include 256 sample, 264 samples, 272 samples, 280 samples, and others within the actual instrument memory size limit.