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Chapter 4 Demo Waveforms
Demo 2: Data-to-Clock
that this value has the potential to create unexpected results for users
who may not have realized a non-zero reference value was applied. Go to
the online help topic "Nulling Timing Skew" for details on how to use the
reference to null external timing skew.
For data-to-clock measurements, the ideal relationship between these
signals is an average time difference of zero. Using the online help
description, the needed reference value was determined to be 38.1 ns.
Enter this value as the reference and select OK. Notice that the statistical
mean, min and max have been re-computed to reflect the change of
reference.
4
Select Segment>Define Segments & Clock.
The segment width has been set to 50 ns which is the decode window
width for this drive. For data-to-clock measurements, the expected
segment center is always ideally zero, so the "1st Segment Center"
parameter is grayed out. (Remember, you adjusted for timing skew in the
prior step.) The "1st Segment Center" parameter is used for data-to-data
measurements. A change in the "Fine Adjust" parameter, will slide the
segment by the amount of the entered value. The "Fine Adjust"
parameter's primary purpose is to allow you to experiment with how
adjusting the decode window position could affect performance.
The "Total Segments" parameter is also grayed out for data-to-clock
measurements because there should ideally be only one distribution.
(There is one situation where more than one distribution may occur, it is
described in the online help topic "Histogram Displays Split
Distribution.") The software automatically provides the correct number of
segments.
Window Margin and Extrapolation Levels
1
Select Display>Window Margin.
2
Maximize this window by clicking on the maximize (
upper right corner of the Window Margin window.
Getting Started Guide
) symbol in the
4-19
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