HP 1660CP Series User Manual page 278

Transitional Mode Theory
250-MHz Transitional mode
probability of a transition falling between a sample pair or falling within a
sample pair.
Maximum transitions stored
The following example shows the case where the transitions are occurring at
a 4-ns rate:
Maximum Transitions Stored
In this case, transitions are being detected with each sample so all samples
are stored. This situation also means each sample pair contains a transition.
For example, time tag 1 (100/000) contains a transition and is different from
time tag 2 (111/011), which also contains a transition. The difference
between the sample pairs of time tag 1 and time tag 2 will trigger the
transition detector.
If this were to continue throughout the trace, the analyzer would store a
single sample for the entire 4 K of memory, or 4096 samples. Again, subtract
one for the initial sample which is not a transition for a final total of 4095
transitions recorded. As with the 125-MHz mode, the actual number of
transitions stored will fall somewhere between 682 and 4095, depending on
the frequency of transitions.
10-10