HP 54645A User's And Service Manual page 83

Triggering HP 54645A/D Oscilloscopes
To define an advanced pattern trigger
Source Operator and
Parameters
Pattern 1 Then
Pattern 2
All Qualifiers must be Satisfied to Trigger the Oscilloscope
When setting up an advanced trigger, remember that all required events must
be satisfied to trigger the oscilloscope.
Pattern 1 and Edge 1 are Shared Sources
Source definitions for Pattern 1 and Edge 1 are shared with the pattern trigger
specification. Thus, source changes will affect that specification, and changes
to the simple pattern trigger specification will affect the definitions of Pattern 1
and Edge 1.
High-Frequency Pattern Reject
When you set a pattern that contains more than one digital channel, and no
edges or analog channels, it is possible that false patterns may occur when two
digital channels change at the same time, due to minor skew differences.
In the previous example, when Q2-Q0 change from 1 to 6, Q2 and Q1 rise at the
same time This provides potential for seeing a false "10" or "01" on those two
channels. In the HP 54645D, we require the pattern to be present long enough to
be sampled at least twice at 400 MHz to eliminate this possibility. This method
prevents false triggers on simultaneous edges.
3-24
Pattern/Edge
L on channels D2, D1, and D0, others don't
care
L on channels 2 and 1, H on channel 0,
others don't care