Tektronix, Inc. P6240, User Manual

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Appendix B: Algorithms
B–14
TLS 216 User Manual
4. The logic scope calculates the hold time according to the following equation:
Setup CrossLastćMCrossClock
Positive setup times indicate that the clock edge occurred after the last transition
of the waveform group. Negative setup times indicate that the clock edge
occurred before the last transition.
Hi Ref
Low Ref
Low Ref
Setup
Time
Clock Transition
Last Transition to
a Legal State
Hi Ref
Figure B–5: Setup Time
Timing measurement. The time between the first transition to an illegal state for
all waveforms in a group and last transition to a legal state for the same
waveforms. Skew measurements define “legal state” as a level either below the
low reference level or above the high reference level that is set in the Measure
menu. They define an “illegal state” as a level between the the low and high
reference levels.
Setup is determined in the following manner (see Figure B–6):
1. The logic scope finds the first
LowRef
crossing and the first
HighRef
crossing for each waveform in the selected group.
2. The logic scope finds the last
LowRef
crossing and the last
HighRef
crossing
for each waveform in the selected group.
3. The logic scope determines which crossing out of all the first crossings
found in step 1 occurred first for the waveform group. The crossing is called
CrossFirst
and might be either a
LowRef
or a
HighRef
crossing.
4. The logic scope determines which crossing out of all the last crossings found
in step 2 occurred last for the waveform group. The crossing is called
CrossLast
and might be either a
LowRef
or a
HighRef
crossing.
Skew