Agilent Technologies 1670E Series, User Manual

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Logic Analyzer Concepts
Transitional Mode Theory (1660E/ES/EP-series only)
Minimum transitions stored
The figure above shows what data is stored from a data stream with
transitions that occur at a slow rate (more than 24 ns apart).
As shown, transitions are stored in two different ways, depending
strictly on chance. Remember that the transition detector only looks at
the full 34 bits while the data is stored as two 17-bit samples. So, the
transition detector will not see time tag 3 (101/000) as a transition.
However, when the detector compares the transition to time tags 2
(101/101) or 4 (000/000), it sees a difference and detects them as
transitions. For this first set of time tags, the transition detector sees
more transitions than are really there. This causes the analyzer to store
6 samples per transition (three 34-bit sample pairs), instead of just
two, as in the 125-MHz mode. If all of the transitions will be stored in
this way throughout the trace, the minimum number of stored
transitions is 682 (4096/6).
However, as you see with time tags 7 (000/000) and 8 (001/001),
transitions can fall between the pairs of samples. When this happens,
only one transition is detected and only 4 samples (two sample pairs)
are stored. If all transitions will be stored in this way, 1023 (4096/4)
transitions are stored.
From run to run, the actual number of transitions stored for transitions
that occur at a slower rate will fall between these two numbers, based
on the probability of a transition falling between a sample pair or falling
within a sample pair.