LabVIEW Example—Hardware-Timed Counter Tasks

Note  Although this example is written for LabVIEW users, the principles apply if you are using another ADE, such as LabWindows/CVI.

• Wire the Wait For Next Sample Clock VI to the counter input task.
• If the Wait For Next Sample Clock VI does execute before the arrival of the next sample clock edge, it returns an error.

Sample Block Diagram

Example 2

• Wire the Wait For Next Sample Clock VI to the counter output task.
• If the Wait For Next Sample Clock VI does not execute before the arrival of the next sample clock edge, it returns an error.

Sample Block Diagram

Notes

• Use only one Wait For Next Sample Clock VI within a LabVIEW loop. If you have multiple hardware-timed I/O tasks within the same LabVIEW loop, you can connect the Wait For Next Sample Clock VI to any one hardware-timed single point task within that loop.
• If, when a cycle overflow occurs, you want to receive a warning rather than an error, set the DAQmx Real-Time»Convert Late Errors to Warnings property to True.
• Hardware-timed counter operations have no conversion period similar to that of multiplexed analog input. Therefore, the real-time FIFO can be placed anywhere within the LabVIEW loop.
• NI-DAQmx provides a mechanism to recover after missing a sample clock edge when performing counter writes. If this write recovery mechanism is not successful, NI-DAQmx returns an error, and subsequent operations on that task are no longer hardware timed.
• The DAQmx Real-Time»Write Recovery Mode property allows you to choose between Wait For Interrupt or Polling mode for the recovery mechanism. Wait For Interrupt, which is the default, allows lower priority processes to execute while NI-DAQmx attempts to recover. Polling mode, on the other hand, allows for higher sampling rates.