8–22
Triggers and When to Use Them
Qualified Triggers offer the choice of generating a trigger either
when the selected pattern is present or absent. As with Pattern
Trigger, the pattern is defined as a logical AND combination of
trigger states that are either high or low: high when a trigger source
is greater than the selected trigger level, and low when it is less
than. For example, a pattern might be defined as present when the
trigger states for Channels 1 and 2 are high and EXT is low. If any of
these conditions is not met, the pattern state is considered absent.
Qualified Triggers allow an additional qualification once the selected
pattern state occurs. For example: “wait for 10 ns up to 20 s, trigger
on CH 1 to the 99 999 999th event”. The pattern is used to qualify
the trigger without actually generating it. Triggering will occur when
another signal, the trigger source, meets its trigger condition while
the pattern is present. The trigger source itself is not allowed in the
pattern.
Applications Typical applications can be found wherever time violations
occur, such as in micro-processor debugging or
telecommunications.
State-Qualified with Wait State-Qualified Trigger with Wait (Fig. 8–17) is determined by
the parameters of Time and number of Events:
Ø Time selects a delay from the start of the desired pattern.
After the delay (timeout) and while the pattern is present, a
trigger can occur. The timing for the delay is restarted when
the selected pattern begins
Ø Events selects a minimum number of events of the trigger
source. An event is generated when a trigger source meets
its trigger conditions. On the selected event of the trigger
source and while the pattern is present, a trigger can occur.
The count is initialized and started whenever the selected
pattern begins, and continues while the pattern remains.
When the selected count is reached, the trigger occurs.
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