Tektronix DPScope II, User Manual

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display mode
– if the signals change fast compared to the sample rate, connecting subsequent
sample points with lines can result in a messy, difficult-to-interpret picture on the screen.
2.2.5 Persist
Normally the screen is cleared whenever the scope has a new acquisition to display. Checking
this option will make the scope keep all waveforms on the screen until you either press “Stop”
and then “Start “ again, or until you press “Clear”. This allows you to see over which range the
waveform is changing; important cases are measurement of peak-to-peak noise or timing jitter.
This is also a great tool to capture rare glitches (sudden waveform aberrations) that you may
miss otherwise because without persist mode they may disappear from the screen again so
quickly that you can’t see them. When persist mode is turned on however even a single such
event with remain easily visible.
Finally a very common application of this mode is to produce so-called data eyes for digital
waveforms. For this purpose choose triggering on “Both” (i.e. rising as well as falling edges) for
the clock waveform, and turning “Lines” off and “Dots” on.
2.2.6 Levels
Turns level markers (and the trigger position marker in pretrigger mode) on and off. While the
levels (CH1 and CH2 offsets, and the trigger threshold) are also indicated with colored triangle
markers on the left edge of the waveform display, sometimes it is helpful to have rulers across
the whole screen. The trigger position in pretrigger mode tells you which portion of the
waveform caused the trigger.
2.2.7 Cursors, CH1, CH2
Turns the measurement cursors on and off, respectively, and selects which channel (CH1 or
CH2) they refer to.
The cursors are the solid horizontal and vertical lines in the waveform display which appear
whenever you check the “Cursors” checkbox. You can move them with the slider bars on
top/bottom and left/right of the waveform display, or alternatively by clicking on them and then
(with mouse button pressed) dragging them to the desired location.
The current level and time positions as well as the difference in their positions are shown in the
status line on the bottom of the scope window:
Because the voltage scales can be different between CH1 and CH2 you need to select which of
these two waveforms the cursors shall refer to. (The time scale is the same for both so this
selection has no bearing on timing measurements, i.e. on the vertical cursors).