Trigger Sub-System
The trigger subsystem configures the type of event that triggers the oscilloscope. The global trigger subsystem attributes are:
The IVISCOPE_ATTR_TRIGGER_TYPE attribute specifies the event that triggers the oscilloscope.
The IVISCOPE_ATTR_TRIGGER_HOLDOFF attribute specifies the length of time after the oscilloscope detects a trigger during which the oscilloscope ignores additional triggers. The IVISCOPE_ATTR_TRIGGER_HOLDOFF attribute only affects instrument operation when the oscilloscope requires multiple acquisitions to build a complete waveform. The oscilloscope requires multiple waveform acquisitions when the instrument uses equivalent time sampling or the acquisition type is set to envelope or average. The IVISCOPE_ATTR_TRIGGER_COUPLING attribute specifies how the oscilloscope couples the trigger source signal to the trigger subsystem.
The attributes from the above list can be set individually or they can be set as a group with the IviScope_ConfigureTrigger and IviScope_ConfigureTriggerCoupling functions.
The following attributes configure the edge trigger. These attributes can be set individually or as a group with the IviScope_ConfigureEdgeTriggerSource function.
Edge Triggers
The IVISCOPE_ATTR_TRIGGER_SOURCE attribute specifies the source the oscilloscope monitors for the trigger event. The IVISCOPE_ATTR_TRIGGER_LEVEL attribute specifies the voltage threshold for the trigger subsystem. Most of the trigger types use the value held in the IVISCOPE_ATTR_TRIGGER_LEVEL attribute.
The IVISCOPE_ATTR_TRIGGER_SLOPE attribute specifies whether a positive or negative edge triggers the oscilloscope.
When the trigger type is edge, the values held in the IVISCOPE_ATTR_TRIGGER_LEVEL and IVISCOPE_ATTR_TRIGGER_SLOPE attributes define the trigger event. The oscilloscope triggers when the trigger source crosses the threshold level with the polarity the IVISCOPE_ATTR_TRIGGER_LEVEL and IVISCOPE_ATTR_TRIGGER_SLOPE attributes specify.
Triggering Overview
The following figure illustrates the relationship of the Trigger event and the acqStartTime parameter to the data the oscilloscope acquires in the waveform record. For this illustration, the trigger type is an edge trigger and the trigger source is a series of pulses. It is important to note that the trigger source can be an analog or digital signal and the trigger type can be any trigger type that this class driver defines.
Holdoff Overview
The following figure shows how the holdoff effects the trigger subsystem. Ideally the trigger event occurs at condition '1', but sometimes the oscilloscope triggers on condition '2' because the signal crosses the trigger level. When you specify a holdoff, the oscilloscope triggers on conditions '1' and '3', and ignores conditions '2' and '4'.
This IviScopeBase Capability group defines functions that retrieve waveforms from the oscilloscope. These functions return the following information:
- The waveform record as an array of voltages
- The time that corresponds to the first point in the waveform array relative to the Trigger Event
- The effective time interval between points in the waveform record