Tektronix CSA7404B, User Manual

Page: 165 / 438

Triggering
CSA7000B Series & TDS7000B Series Instruments User Manual
3- 97
Overview Control elements and resources Trigger on a pattern (Cont.)
To set mode
and holdoff
8. Mode and holdoff can be set for all standard trigger
types.
See To set holdoff on page 3--74 and To select the
trigger mode on page 3--71 for mode and holdoff
setup. To learn more about trigger mode and
holdoff, see Trigger Modes on page 3--65 and
Trigger Holdoff on page 3--66.
To define a time
qualified pattern
trigger
You can time qualify a pattern logic trigger. That is, you
specify a time that the boolean logic function (AND, NAND,
OR, or NOR) must be TRUE. To specify the time limit as well
as the type of time qualification (More Than or Less Than the
time limit specified) for a pattern trigger, do the following
step:
9. Select Pattern More Than, and set the time using the
multipurpose knob or keypad.
When you select TRUE for Less Than and specify a
time, the input conditions that you specify must drive the
logic function high (TRUE) for less than the time you
specify. Conversely, the TRUE for More Than item
requires the boolean function to be TRUE for longer
than the time that you specify.
Note the position of the trigger indicator. Triggering
occurs at the point that the instrument determines that
the logic function that you specify is TRUE within the
time that you specify. The instrument 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 (for TRUE for more than) or shorter (for
TRUE for less than), 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 (5.2
s) than that set in the TRUE for More Than
item (2 s), the instrument issues the trigger at that
point, not at the point at which it has been TRUE for
2
s.
Logic function (AND)
becomes TRUE
Logic function becomes
FALSE and triggers
acquisition
Time logic function is TRUE
Time Logic Function Must be TRUE = 2 s