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Analog Output
To generate analog output, insert an analog output C Series I/O module in any slot on the cDAQ
chassis. The generation specifications, such as the number of channels, channel configuration,
update rate, and output range, are determined by the type of C Series I/O module used. For more
information, refer to the documentation included with your C Series I/O module(s).
On a single analog output C Series module, you can assign any number of channels to either a
hardware-timed task or a software-timed (single-point) task. However, you cannot assign some
channels to a hardware-timed task and other channels (on the same module) to a software-timed
task. Furthermore, you cannot run multiple tasks of any type on a single analog output module.
(NI cDAQ-9174/9178) With multiple analog output modules, you can have as many
software-timed tasks as there are modules in the chassis, but you can still have only one
hardware-timed task. Any hardware-timed task or software-timed task can have channels from
multiple modules in the same chassis.
Analog Output Data Generation Methods
When performing an analog output operation, you either can perform software-timed or
hardware-timed generations. Hardware-timed generations must be 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 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 generations to simultaneously update
• Only one simultaneous update task can run at a time
• Software-timed generations are limited to 16 channels. Refer to the specifications
document for your cDAQ chassis for more information.
Note Simultaneous update is not limited because it uses hardware-timed generation
with onboard regeneration.
• A hardware-timed AO task and a simultaneous update AO task cannot run at the same time
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