4 Triggering
142 InfiniiVision 7000B Series Oscilloscopes User’s Guide
TV Triggering Examples
The following are exercises to familiarize you with TV triggering. These
exercises use the NTSC video standard.
To trigger on a specific line of video
TV triggering requires greater than 1/2 division of sync amplitude with
any analog channel as the trigger source. Turning the trigger Level knob in
TV trigger does not change the trigger level because the trigger level is
automatically set to the sync pulse tips.
One example of triggering on a specific line of video is looking at the
vertical interval test signals (VITS), which are typically in line 18. Another
example is closed captioning, which is typically in line 21.
1 Press the [Trigger] key; then, select TV.
2 Press the Settings softkey, then press the Standard softkey to select the
appropriate TV standard (NTSC).
3 Press the Mode softkey and select the TV field of the line you want to
trigger on. You can choose Line:Field1, Line:Field2, or Line:Alternate.
4 Press the Line # softkey and select the number of the line you want to
examine.
Line Number Represents Count
In Generic mode, the line number represents the number of a count instead of a real line
number. This is reflected in the label in the softkey changing from Line to Count. In the
Mode softkey selections, Line:Field 1, Line:Field 2 and Count:Vertical are used to indicate
where the counting starts. For an interlaced video signal, the counting starts from the rising
edge of the first vertical serration pulse of Field 1 and/or Field 2. For a non-interlaced video
signal, the counting starts after the rising edge of the vertical sync pulse.
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