250-Mhz Transitional Mode - HP 1660CS-Series User Manual

Transitional Mode Theory

250-MHz transitional mode

Storing time tags and transitions
Maximum transitions stored
If transitions occur at a fast rate, such that there is a transition at each
sample point, only one sample is stored for each transition as shown by time
tags 17 through 21 above. If this continues for the entire trace, the number of
transitions stored is 2 K divided by 1 sample per transition. Again, you must
subtract the starting point sample, yielding a maximum of 2047 stored
transitions.
In most cases a transitional timing trace is stored by a mixture of the
minimum and maximum cases. Therefore, the actual number of transitions
stored will be between 1023 and 2047.
250-MHz transitional mode
Transitional timing running at 250 MHz is the same as the 125-MHz mode,
except that two single-pod data samples are stored instead of one
full-pod-pair data sample. This is because in half-channel mode, data is
multiplexed into the pipeline in two samples. The first sample is latched, and
at the next sample both samples are sent down the pipeline.
This operation keeps the pipeline frequency at 125 MHz, which means the
transition detector still looks at a full 34 bits. Essentially, the transition
detector is looking at two samples at a time instead of one. In the 250-MHz
mode, between 682 and 4094 transitions are stored.
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