User`s guide

2 Targets and Scopes in the MATLAB Interface
2-12
• Freerun — Starts to acquire data as soon as the scope is started (default)
•
Software — Starts to acquire data in response to a user request. You
generate a user request when you call the scope method
trigger or the scope
function
xPCScSoftwareTrigger
• Signal — Starts to acquire data when a particular signal has crossed a
preset level
•
Scope — Starts to acquire data based on when another (triggering) scope
starts
You can use several properties to further refine when a scope acquires data.
For example, if you set a scope to trigger on a signal (
Signal trigger mode), you
can configure the scope to specify the following:
• The signal to trigger the scope (required)
• The trigger level that the signal must cross to trigger the scope to start
acquiring data
• Whether the scope should trigger on a rising signal, falling signal, or either
one
In the following topics, the trigger point is the sample during which the scope
trigger condition is satisfied. For signal triggering, the trigger point is the
sample during which the trigger signal passes through the trigger level. At the
trigger point, the scope acquires the first sample. By default, scopes start
acquiring data from the trigger point onwards. You can modify this behavior
using the pre- and posttriggering.
• Pre-triggering — Starts to acquire data N moments before a trigger occurs
• Post-triggering — Starts to acquire data N moments after a trigger occurs
The
NumPrePostSamples scope property controls the pre- and posttriggering
operation. This property specifies the number of samples to be collected before
or after a trigger event.
• If
NumPrePostSamples is a negative number, the scope is in pretriggering
mode, where it starts collecting samples before the trigger event.
• If
NumPrePostSamples is a positive number, the scope is in a posttriggering
mode, where it starts collecting samples after the trigger event.
The following topics describe two examples of acquiring data: