Marker Events

NI Signal Generators Help (NI-FGEN 18.1)

Edition Date: April 2018

Part Number: 370524V-01

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A marker is an event that the device generates in relation to a generated waveform. The event is configured to occur at the time that a specific location or sample n in the waveform generates on the analog output connector. If the waveform loops multiple times in a segment, the marker generates each time the waveform loops. The following figure shows a pulse that represents a waveform sample n that is one Sample clock in width of a waveform being generated on the analog output connector. The second pulse, the Marker event, represents the pulse that generates when the corresponding waveform sample n outputs at the analog output connector. Refer to Features Supported to determine if your device supports markers.

tm1 represents the delay in time of the Marker event generated relative to the configured waveform sample n being generated.

tm2 represents the Marker event pulse width in time.

NI-FGEN takes into account the factors that affect the delays in the Digital and Analog paths in assuring that the Marker event appears within one Sample clock of the waveform output. Therefore, t m1 is less than one Sample clock period.

The Marker event pulse width, tm2, is at least 150 ns and can be significantly longer than 150 ns for slower Sample clocks. You can configure the pulse width by setting the Marker Event Pulse Width property or the NIFGEN_ATTR_MARKER_EVENT_PULSE_WIDTH attribute. Instruments commonly have a minimum pulse width specification for a trigger to be registered, and trigger pulses of smaller width are ignored. The signal generator ensures that a minimum pulse width exists on the Marker event by using a pulse stretching circuit. A Sample clock rate of 100 MS/s has a period of 10 ns, requiring the pulse to be lengthened for many devices to register the marker as a good trigger pulse. Refer to the device specifications for the timing specifications.

Markers as Trigger Outputs

A delay of at least 44 Sample clocks exists between the Start trigger and the analog waveform generation on the output connector. Therefore, synchronizing the signal generator output signal to other devices with fast trigger response times is accomplished using the Marker event from the signal generator as the trigger source for the other device for more precise alignment to the generating waveform. You can do this using the RTSI bus, PXI trigger lines, or PFI terminals.

Related Topics

Creating a Marker Event

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