software-timed digital output tasks on a single module. On serial digital output modules
(formerly known as static digital output modules), you cannot mix hardware-timed and
software-timed tasks, but you can run multiple software-timed tasks.
You may have a hardware-timed task or a software-timed task include channels from multiple
modules, but a hardware-timed task may not include a mix of channels from both parallel and
serial modules. Multiple timing engines allow the cRIO controller to run up to eight hardware-
timed digital output tasks simultaneously, each using independent timing and triggering
configurations. The eight output timing engines are ot0, ot1,…ot7. All eight of the output
timing engines are shared between analog output and digital output tasks, allowing up to 8
hardware-timed output tasks.
Digital Output Data Generation Methods
When performing a digital output operation, you either can perform software-timed
generations or hardware-timed generations.
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 digital generation. 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.
For software-timed generations, if any DO channel on a serial digital module is used in a
hardware-timed task, no channels on that module can be used in a software-timed task.
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 controller 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 Single Point (HWTSP) Mode
In HWTSP mode, samples are acquired or generated continuously using hardware timing and
no buffer. You must use the sample clock or change detection timing types. No other timing
types are supported.
Use HWTSP mode if you need to know if a loop executes in a given amount of time, such as
in a control application. Because there is no buffer, if you use HWTSP mode, ensure that reads
or writes execute fast enough to keep up with hardware timing. If a read or write executes late,
it returns a warning.
NI cRIO-905x User Manual
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© National Instruments
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