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Minimizing Glitches on the Output Signal
When you use a DAC to generate a waveform, you may observe glitches on the output signal.
These glitches are normal; when a DAC switches from one voltage to another, it produces
glitches due to released charges. The largest glitches occur when the most significant bit (MSB)
of the DAC code switches. You can build a lowpass deglitching filter to remove some of these
glitches, depending on the frequency and nature of the output signal. Visit
for more information on minimizing glitches.
AO Data Generation Methods
When performing an analog output operation, there are several different data generation
methods available. You can either perform software-timed or hardware-timed generations.
Hardware-timed generations can be non-buffered or buffered.
Software-Timed Generations
With a software-timed generation, software controls the rate at which data is generated. Software
sends a separate command to the hardware to initiate each DAC conversion. In NI-DAQmx,
software-timed generations are referred to as On Demand timing. Software-timed generations
are also referred to as immediate or static operations. They are typically used for writing a single
value out, such as a constant DC voltage.
Hardware-Timed Generations
With a hardware-timed generation, a digital hardware signal controls the rate of the generation.
This signal can be generated internally on your device or provided externally.
Hardware-timed generations have several advantages over software-timed generations:
•
The time between samples can be much shorter.
•
The timing between samples can be deterministic.
•
Hardware-timed generations can use hardware triggering. For more information, refer to
Chapter 10, Triggering.
Hardware-timed operations can be buffered or non-buffered. A buffer is a temporary storage in
computer memory for acquired or to-be-generated samples.
Buffered
In a buffered generation, data is moved from a PC buffer to the DAQ device's onboard FIFO
using DMA or interrupts before it is written to the DACs one sample at a time. Buffered
generations typically allow for much faster transfer rates than non-buffered generations because
data is moved in large blocks, rather than one point at a time. For more information on DMA and
interrupt requests, refer to the
One property of buffered I/O operations is the sample mode. The sample mode can be either
finite or continuous.
Data Transfer Methods
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