Digital Output Timing Signals

The sbRIO controller features the following DO timing signals:
  • DO Sample Clock Signal*
  • DO Sample Clock Timebase Signal
  • DO Start Trigger Signal*
  • DO Pause Trigger Signal*

Signals with an * support digital filtering. Refer to the PFI Filters section for more information.

DO Sample Clock Signal

The DO Sample Clock signals when all the digital output channels in the task update. DO Sample Clock can be generated from external or internal sources as shown in the image below.

Figure 22. Digital Output Timing Options

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Routing DO Sample Clock to an Output Terminal

You can route DO Sample Clock to any output PFI terminal. DO Sample Clock is active high by default.

DO Sample Clock Timebase Signal

The DO Sample Clock Timebase signal is divided down to provide a source for DO Sample Clock. DO Sample Clock Timebase can be generated from external or internal sources and is not available as an output from the controller.

DO Start Trigger Signal

Use the DO Start Trigger signal to initiate a waveform generation. If you do not use triggers, you can begin a generation with a software command. If you are using an internal sample clock, you can specify a delay from the start trigger to the first sample. For more information, refer to the NI-DAQmx Help.

Using a Time Source

To use the Start Trigger signal with a time source, configure a specific time in NI-DAQmx. Refer to the "Timestamps" and "Time Triggering" topics in the NI-DAQmx Help for more information on accessing time-based features in the NI-DAQmx API.

Using a Digital Source

To use DO Start Trigger, specify a source and a rising or falling edge. The source can be one of the following signals:

  • A pulse initiated by host software

  • Any PFI terminal

  • AI Reference Trigger

  • AI Start Trigger

The source also can be one of several internal signals on the sbRIO controller. Refer to the "Device Routing in MAX" topic in the NI-DAQmx Help or the LabVIEW Help for more information.

You also can specify whether the waveform generation begins on the rising edge or falling edge of DO Start Trigger.

Routing DO Start Trigger Signal to an Output Terminal

You can route DO Start Trigger to any output PFI terminal. The output is an active high pulse.

DO Pause Trigger Signal

Use the DO Pause Trigger signal to mask off samples in a DAQ sequence. When DO Pause Trigger is active, no samples occur, but DO Pause Trigger does not stop a sample that is in progress. The pause does not take effect until the beginning of the next sample.

When you generate digital output signals, the generation pauses as soon as the pause trigger is asserted. If the source of the sample clock is the onboard clock, the generation resumes as soon as the pause trigger is deasserted, as shown in the figure below.

Figure 23. DO Pause Trigger with the Onboard Clock Source

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If you are using any signal other than the onboard clock as the source of the sample clock, the generation resumes as soon as the pause trigger is deasserted and another edge of the sample clock is received, as shown in the figure below.

Figure 24. DO Pause Trigger with Other Signal Source

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Using a Digital Source

To use DO Pause Trigger, specify a source and a polarity. The source can be a PFI signal or one of several other internal signals on the sbRIO controller.

You also can specify whether the samples are paused when DO Pause Trigger is at a logic high or low level. Refer to the "Device Routing in MAX" topic in the NI-DAQmx Help or the LabVIEW Help for more information.