CompactRIO Considerations

Slot Program Mode

In MAX, when you add a C Series module to a CompactRIO controller there are three program modes to choose from.

• Real-Time (NI-DAQmx)
• Real-Time Scan
• LabVIEW FPGA

In order for DAQmx to communicate with the module, the module must be in Real-Time (NI-DAQmx) mode.

Note  

Not all modules support Real-Time (NI-DAQmx).

Hardware Timed Single Point Sample Mode

The CompactRIO controllers support hardware timed single point (HWTSP) sample mode with a few caveats.

• The NI 9260 does not support HWTSP.
• The NI 9361 does not support HWTSP.
• C Series Scanned Devices do not default to the lowest latency mode. They default to a slower convert rate to allow more time for settling. This behavior limits the maximum HWTSP acquisition rate of the module to allow more time for settling. If you prefer, you can configure the module for a faster acquisition rate with less time for settling. For additional information, see Sampling Rate Considerations.

Model Names

CompactRIO may use slightly different C Series model names and product IDs compared to CompactDAQ. For CompactRIO, see C Series Module IDs on ni.com.

Timing Considerations

CompactRIO controllers handle sampling rate and the default value for the hardware-timed mode differently than CompactDAQ chassis.

In a CompactRIO or Single-Board RIO controller with C Series Slow Sample devices, such as the NI 9211, if the sampling rate of a hardware-timed acquisition exceeds the maximum sampling rate of the module, DAQmx generates warning or errors. When a Slow Sample device is in the same task as a non-Slow Sample device, exceeding the maximum sampling rate of the Slow Sample device results in the most recently acquired sample being read multiple times. In this scenario, the first sample of a hardware-timed acquisition with C Series Slow Sample devices is sampled when the task is committed.

Default Settings for the AI.ADCTimingMode Attribute/Property

For all modules in the CompactRIO and Single-Board RIO controllers, the default value in hardware-timed mode is automatically determined based on Sample Clock Rate.

Shared Trigger Bus

On the CompactRIO and CompactRIO Single-Board controllers, NI-DAQmx provides a simple trigger bus between LabVIEW FPGA and NI-DAQmx with the following characteristics:

Note  

The signals available for export from DAQmx vary in pulse width. On a cRIO controller, if you route any of the following signals over the cRIO_Trig bus to the FPGA Target, the pulse is too short to be seen in the default top level clock domain of 40 MHz:

• Change detection event exported from a buffered change detection DI task
• Sample clock exported from a hardware-timed digital input or output task running faster than 3.5 MHz

• Counter output event exported from a counter task that configures its output behavior to pulse

To fix this problem, consider routing the signal to a counter to widen the pulse.

NI cRIO Trigger Bus Terminals

There are two new sets of general-purpose input/output lines for sharing signals between NI-DAQmx tasks and FPGA IO on a NI cRIO chassis.

• cRIO_Trig0, cRIO_Trig1, cRIO_Trig2, and cRIO_Trig3 are terminals that are driven from the LabVIEW FPGA to NI-DAQmx.
• cRIO_Trig4, cRIO_Trig5, cRIO_Trig6, and cRIO_Trig7 are terminals that are driven from NI-DAQmx to LabVIEW FPGA.