Generally, triggers and clocks are input signals but 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 hardware events. Events are generated 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 hardware 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 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 Transfer Event—A signal sent to the peripheral device that signals 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.
To set these events in LabVIEW use the DAQmx Export Signal Property Node. This is located in LabVIEW under Measurement I/O >>DAQmx-Data acquisition >> DAQmx Advanced Task Options >> DAQmx Export Signal as shown in Figure 1.
Figure 1. DAQmx Export Signal Property Node
With the DAQmx Export Signal Property Node, you can select the Event polymorphic instance such as AI Hold Complete Events, Change Detection Events, Counter Output Events as shown in Figure 2.
Figure 2 Counter output event properties
Others are located in in LabVIEW under Measurement I/O >>DAQmx-Data acquisition >> DAQmx Advanced Task Options sub-palette and in LabVIEW under Measurement I/O >>DAQmx-Data acquisition >> DAQmx Device Configuration >> watchdog sub-palette.