Table Of Contents


Last Modified: January 31, 2020

Triggers and clocks are input signals. Exportable triggers and clocks, such as the sample clock, also can be output signals. Output signals that do not have a trigger or clock counterpart are called events. Events are emitted to signify a device state change, the arrival of a certain kind of sample, the production of a certain amount of samples, or the passage of time.

NI-DAQmx includes the following events:

  • Advance Complete Event—A signal emitted by a switch when it has finished executing an instruction in its scan list.
  • AI Hold Complete Event—A signal emitted by a multiplexed analog input circuit when the analog signal at the physical channel being measured has been latched or held. The AI Hold Complete Event is designed to signal an external multiplexer to switch to the next channel. This signal was previously known as SCANCLK, which is the legacy name of the external terminal where this signal can be emitted.
  • Change Detection Event—A signal a DIO device generates after it detects a change-a rising edge, a falling edge, or both rising and falling edges-on the data lines.
  • Counter Output Event—A signal produced by a counter when it reaches terminal count.
  • Handshake Event—A signal generated by a DAQ device that is used for handshaking. The assertion and deassertion times for this event are configurable within a handshaking cycle for some devices. For these devices, the default configuration is to mimic the 8255 protocol, which means that for input tasks, this event asserts after the device has space available in its FIFO; for output tasks, it asserts after valid data has been driven on the data lines; and in both input and output tasks, the event deasserts after the Handshake Trigger has been asserted.
  • Ready For Start Event—A signal produced when a device is ready to accept a Start Trigger.
  • Ready For Transfer Event—A signal sent to the peripheral device. The signal indicates that the DAQ device is ready for a transfer. For burst handshake output tasks, this means that the data is on the data lines. For input tasks, this means that there is space available in the device FIFO. This event is used by devices that support burst handshake timing.
  • Sample Complete Event—A signal produced when the device acquires a sample from every channel in a task.
  • Watchdog Timer Expired Event—A signal produced when a watchdog timer expires. Watchdog timers are hardware features that can detect failures in the software controlling the device.

The Sample Complete Event is not exportable.


Some event signals might be missed when you run an application. This typically happens with high-speed event sources. NI-DAQmx does not generate an error if this occurs.

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