Tektronix TDS5054, Руководство пользователя

Страница: 148 / 361

Triggering
TDS5000 Series User Manual
3- 81
Overview Control elements and resources To trigger on a pattern
To define a time
qualified pattern
trigger
9. You can time qualify a pattern logic trigger, that is, you
can specify the amount of time that the Boolean logic
function must be True. You must select Less than or
More Than for the Trigger When Pattern control. Then,
click on Trigger When Time and set the time using the
multipurpose knob or keypad.
When you select Less Than and specify a time, the
input conditions must drive the logic function True for
less than the specified time. Conversely, the True for
More Than item requires the Boolean function to be
True for longer than the time you specify.
The oscilloscope determines the trigger point in the
following manner:
H
It waits for the logic condition to become True.
H
It starts timing and waits for the logic function to
become False.
H
It compares the times and, if the time True is longer
(More Than Time) or shorter (Less Than Time),
then it triggers a waveform display at the point the
logic condition became False. This time can be,
and usually is, different from the time set.
In the figure, the delay between the vertical bar cursors
is the time the logic function is True. Since this time is
more (4.9 ns) than the More Than Time (3.0 ns), the
oscilloscope issues the trigger at that point, not at the
point at which it has been True for 3.0 ns.
Logic function (AND)
becomes TRUE
Logic function becomes
FALSE and triggers
acquisition
Time logic
function is TRUE
Time Logic Function Must be TRUE = 3.0 ns