© National Instruments Corporation 21 NI cDAQ-9172 User Guide and Specifications
referred to as immediate or static operations. They are typically used for
writing out a single value, such as a constant DC voltage.
The following considerations apply to software-timed generations:
If any AO channel on a module is used in a hardware-timed
(waveform) task, no channels on that module can be used in a
software-timed task.
You can configure software-timed generation to simultaneously
update.
Only one simultaneous update task can run at a time.
Simultaneous update is not restricted to 16 channels.
A hardware-timed AO task and a simultaneous update AO task cannot
run at the same time.
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 the chassis
or provided externally.
Hardware-timed generations have several advantages over software-timed
acquisitions:
The time between samples can be much shorter.
The timing between samples is deterministic.
Hardware-timed acquisitions can use hardware triggering.
Hardware-timed AO operations on the NI cDAQ-9172 chassis must be
buffered.

Buffered Analog Output

A buffer is a temporary storage in computer memory for generated
samples. In a buffered generation, data is moved from a host buffer to the
NI cDAQ-9172 onboard FIFO before it is written to the C Series I/O
modules.
One property of buffered I/O operations is sample mode. The sample mode
can be either finite or continuous.
Finite sample mode generation refers to the generation of a specific,
predetermined number of data samples. Once the specified number of
samples is written out, the generation stops.
Continuous generation refers to the generation of an unspecified number of
samples. Instead of generating a set number of data samples and stopping,