SDK Advanced Triggers

Advanced Triggers – Setup and Logic #

A trigger event can occur when one of the signal or trigger input channels crosses a threshold voltage on either a rising or a falling edge, or when a more complex time-qualified condition occurs. It is also possible to combine multiple analog and digital inputs and time-qualified conditions using the logic trigger function.

The format to configure an advanced trigger is detailed below. You first must form an array of each type of structure. The trigger logic is the logical AND of structures in the array. Then call the related function, passing in each array. For example, if a rising edge is set for both A and B in same array, they are logically ANDed and a rising edge must seen on both A and B for the scope to trigger. For a logical OR, create an array for each ORed input and call the related function, passing each array. So for a 4-channel-input logic OR, create four sets of arrays for each structure type and pass the corresponding arrays related to each function.

Form an array of structures:

PSXXXX_XXXXX array[] ={

PSXXXX_XXXXX structure1

PSXXXX_XXXXX structure2,

PSXXXX_XXXXX structureN

}

Note; Some driver/APIs have V2 trigger structures and functions. It is now recommended to use these for new examples.

This general overview of how the trigger APIs work. Please refer to the specific API programmer’s guide for your model of PicoScope.

TRIGGER_CHANNEL_PROPERTIES structure #

Upper and lower thresholds #

The digital triggering hardware in your PicoScope has two independent trigger thresholds called upper and lower. For some trigger types you can freely choose which threshold to use. See PSXXXX_THRESHOLD_DIRECTION on the following pages for a list of trigger types and the thresholds that they support. Dual thresholds are used for pulse-width triggering, when one threshold applies to the level trigger and the other to the pulse-width qualifier; and for window triggering, when the two thresholds define the upper and lower limits of the window. Each threshold has its own trigger and hysteresis settings.

Note: Some of our example SDK code like the C# examples use different names for the thresholds:

Upper is called Major

Lower is called Minor

Hysteresis #

Each trigger threshold (upper and lower) has an accompanying parameter called hysteresis. This defines a second threshold at a small offset from the main threshold. The trigger fires when the signal crosses the trigger threshold, but will not fire again until the signal has crossed the hysteresis threshold and then returned to cross the trigger threshold. The double-threshold mechanism prevents noise on the signal from causing unwanted trigger events.

For a rising-edge trigger the hysteresis threshold is below the trigger threshold. After one trigger event, the signal must fall below the hysteresis threshold before the trigger is enabled for the next event. Conversely, for a falling-edge trigger, the hysteresis threshold is always above the trigger threshold. After a trigger event, the signal must rise above the hysteresis threshold before the trigger is enabled for the next event.

Note: Hysteresis values are specified in ‘scaled ADC counts’ (16-bit variables). So you should use values for your scope’s actual hardware resolution, x per ADC step;

8-bit scope – (scaled ±32 512, +7F00 hex), 254 per ADC step

12-bit scope – (scaled ±32 767, +7FFF hex), 16 per ADC step

14-bit scope – (scaled ±32 767, +7FFF hex),   4 per ADC step

15-bit scope – (scaled ±32 767, +7FFF hex),   2 per ADC step

The trigger fires at A as the signal rises past the trigger threshold. It does not fire at B because the signal has not yet dipped below the hysteresis threshold. The trigger fires again at C after the signal has dipped below the hysteresis threshold and risen again past the trigger threshold.

THRESHOLD_DIRECTION constants #

Constant	Trigger Type	Threshold	Polarity	Example Waveform
PSXXXX_ABOVE	Gated	Upper	Above
PSXXXX_ABOVE_LOWER	Gated	Lower	Above
PSXXXX_BELOW	Gated	Upper	Below
PSXXXX_BELOW_LOWER	Gated	Lower	Below
PSXXXX_RISING	Threshold	Upper	Rising
PSXXXX_RISING_LOWER	Threshold	Lower	Rising

THRESHOLD_DIRECTION constants #

Constant	Trigger Type	Threshold	Polarity	Example Waveform(s)
PSXXXX_FALLING	Threshold	Upper	Falling
PSXXXX_FALLING_LOWER	Threshold	Lower	Falling
PSXXXX_RISING_OR_FALLING	Threshold	Lower ->Upper ->	For RisingFor Falling
PSXXXX_INSIDE	Window-qualified	Both	Inside
PSXXXX_OUTSIDE	Window-qualified	Both	Outside
PSXXXX_ENTER	Window	Both	Entering

THRESHOLD_DIRECTION constants #

Constant	Trigger Type	Threshold	Polarity	Example Waveform(s)	Notes
PSXXXX_EXIT	Window	Both	Falling
PSXXXX_ENTER_OR_EXIT	Window	Both	Falling
PSXXXX_POSITIVE_RUNT	Window-qualified	Both	Entering from below the window		A portion of a signal that crosses Upper threshold and then subsequently crosses Upper threshold again without first crossing Lower threshold.
PSXXXX_NEGATIVE_RUNT	Window-qualified	Both	Entering from above the window		Same as above
PSXXXX_NONE	None	None	None

Pulse-width qualifier #

The direction of the signal required for the pulse width trigger to fire. See PXXXX_THRESHOLD_DIRECTION constants for the list of possible values.

Each channel of the oscilloscope (except the EXT input) has two thresholds for each direction—for example, PSXXXX_RISING and PSXXXXX_RISING_LOWER—so that one can be used for the pulse-width qualifier and the other for the level trigger.

The driver will not let you use the same threshold for both triggers; so, for example, you cannot use PSXXXX_RISING as the direction argument for both psXXXXSetTriggerConditions and psXXXXSetPulseWidthQualifier a

t the same time. There is no such restriction when using window triggers.

Pulse-width qualifier #

PWQ – Upper and lower thresholds #

The pulse width, delay and drop-out triggering methods additionally require the use of the pulse-width qualifier functions:

psXXXXSetPulseWidthQualifierProperties

psXXXXSetPulseWidthQualifierConditions

psXXXXSetPulseWidthQualifierDirections

Function Arguments #

psXXXXSetPulseWidthQualifierProperties

lower, the lower limit of the pulse-width counter, in samples. This argument is required for all pulse width types.

upper, the upper limit of the pulse-width counter, in samples. This argument is used only when the type is PSXXXX_PW_TYPE_IN_RANGE or PSXXXX_PW_TYPE_OUT_OF_RANGE. 

type, the type of pulse width trigger. See PSXXXX_PULSE_WIDTH_TYPE.

psXXXXSetPulseWidthQualifierConditions

conditions, a list of PSXXXX_CONDITION structures

nConditions, the number of values in the conditions list

info, whether to add this condition to the existing definition or clear the definition and start a new one. See PSXXXX_CONDITIONS_INFO.

psXXXXSetPulseWidthQualifierDirections

directions, a list of PSXXXX_DIRECTION structures specifying which direction to apply to each trigger source nDirections, the number of items in the directions list.

PSXXXX_PULSE_WIDTH_TYPE constants #

Constant	Time Threshold(s)	Range	Example Waveform(s)
PSXXXX_PW_TYPE_LESS_THAN	Lower	Less Than
PSXXXX_PW_TYPE_GREATER_THAN	Lower	Greater Than
PSXXXX_PW_TYPE_IN_RANGE	Both	Inside both
PSXXXX_PW_TYPE_OUT_OF_RANGE	Both	Outside both
PSXXXX_PW_TYPE_NONE	None	None