National Instruments 5411 - Manual (Page 30)

Chapter 4 Arb Operation
© National Instruments Corporation 4-5 DAQArb 5411 User Manual
Minimum Buffer Size and Resolution
The 5411 device memory architecture imposes certain restrictions on
the buffer size and resolution. The minimum buffer size for Arb mode
is 256 samples and the buffers must be in multiples of eight samples.
For example, if you request the DAQArb to load a buffer of 257
samples, NI-DAQ will truncate the buffer to 256 samples. The last
sample will not be loaded into the memory.
Note: If the minimum buffer size of 256 samples is not met, NI-DAQ will return
an error.
Note: If the buffer is not a multiple of eight samples, NI-DAQ will return a
warning and truncate the buffer to the nearest multiple of eight samples.
Waveform Linking and Looping
Before you can start generating waveforms, you have to load the buffers
on your DAQArb 5411. Each signal to be generated loads into the
memory in the form of 16-bit digital samples. A finite number of these
samples makes a waveform buffer, sometimes also referred to as a
waveform segment. You can load multiple buffers in the memory on
DAQArb 5411. To generate these buffers, you have to prepare a staging
list, also known as a sequence list, which contains a sequence of stages.
Each stage specifies the buffer to be generated, the number of loops on
that buffer, and the marker position for that buffer.
Figure 4-4 illustrates the concept of waveform samples, buffer, stage,
staging list, and looping and linking. Waveform sample A shows the
concept of waveform samples used to create a waveform, shown in
waveform buffer 1. In this example, the waveform buffer 1 represents a
single cycle of a sine wave and the waveform samples in sample A are
16-bit samples. Waveform stage 1 shows a stage created from buffer 1.
Stage 1 is buffer 1 with three cycle iterations.
Waveform sample B shows samples for waveform buffer 2, which
represents a triangular waveform. Waveform stage 2 is created using
two iterations of buffer 2.
Stage 3 is created using a single iteration of buffer 1. These waveforms
are linked in a sequence, as shown in Figure 4-4. The concept of using
a staging list to generate waveforms is referred to as waveform linking
and looping or waveform staging.