HP 54645A User's And Service Manual page 72

Triggering HP 54645A/D Oscilloscopes
Trigger types
Glitch Trigger
The advanced glitch trigger menu lets you select the analog (A1 or A2) or
digital (D0-D15) channel on which to capture a glitch event. You specify the
polarity and duration qualifier—either less than (<), greater than (>), or a
range—for the glitch. The HP 54645D can capture glitches >8 nanoseconds
and <100 seconds.
Pattern Trigger
In pattern trigger, you define a pattern of highs, lows, and don't care levels
that must be recognized across the input channels. The pattern may be
combined with one edge on any one input channel to form the complete
trigger specification.
A Pattern trigger is best when there is a unique pattern that occurs across a
group of signals, and the pattern defines the events you want to capture. For
example, suppose you have a state machine that outputs a series of hex
digits, and only outputs the digit "A" once in every sequence. You can use a
pattern trigger to capture this event, perhaps qualified with the state
machine clock.
Pattern trigger is less useful when the same pattern occurs many times, and
most of those occurrences have little to do with the events you want to
capture. For example, suppose that this same state machine generates
hundreds of states, and the state "C" occurs several times in the sequence,
with a different sequence of states after each occurrence. A pattern trigger
will not provide a stable waveform display.
The pattern trigger occurs when the pattern is entered; that is, the trigger
condition is satisfied as soon as the input waveforms have transitioned from a
condition not matching the pattern to a condition matching the pattern. You
can use an edge to further qualify the trigger condition. For example, you
may want the oscilloscope to trigger when a certain pattern is present and a
clock edge occurs.
The trigger pattern can include high and low values on the oscilloscope A1
and A2 channels. You control the trigger level with the Analog Level knob.
Logical Combination within Terms
In the pattern trigger, all settings within the pattern are logically ANDed; that
is, all conditions on the pattern, and the edge if specified, must be satisfied
before the oscilloscope will trigger.
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