25
Trigger System
6 .3 .4 Video Trigger
The video trigger allows you to trigger on PAL, NTSC
SECAM standard video signals or on HDTV signals. After
selecting the VIDEO trigger press the SOURCE
32
key. The
FILTER
36
menu allows you to define additional settings.
The oscilloscope triggers if the CVBS signal (Color Video
Baseband Signal) selected in the SOURCE menu features
the attributes set in the FILTER menu. Select the desired
standard by pressing the respective soft menu key STAN-
DARD. Use the universal knob in the CURSOR/MENU sec-
tion or press the soft menu key again to select the desired
standard. The following modes are available:
❙
PAL
❙
NTSC
❙
SECAM
❙
PAL-M
❙
SDTV 576i
Interlaced
❙
HDTV 720p
Progressive
❙
HDTV 1080p
Progressive
❙
HDTV 1080i
Interlaced
The second setting will apply to the polarity of the sync
pulse (may be positive or negative). With positive video
modulation (the highest brightness is represented in the
image by the maximum signal voltage), the synchroniza-
tion pulses are negative, with negative modulation they
are positive. The slopes of the synchronization pulses are
used for triggering which explains why a faulty polarity
setting causes irregular triggering by image information.
Next you can select between frame triggering (FRAME)
and line triggering (LINE). Selecting LINE allows you to
define the exact line between 1 and 625 via universal knob
or the KEYPAD button in the CURSOR/MENU section. The
soft menu item ALL LINES enables the oscilloscope to
trigger on the start of the lines in the video signal. This key
selects all lines i.e. even when other trigger conditions are
met, the oscilloscope will trigger on each line. If FRAME
is selected for frame triggering, the lower menu items will
allow to trigger on ODD or only EVEN half frames. In this
case, the oscilloscope will trigger on the start of the half
frames in the video signal. The respective key will select
the odd (even) half frames, i.e. even if the other trigger
conditions are met, the oscilloscope will trigger on each
odd (even) half frame.
Fig. 6.5: Video trigger menu
6 .3 .5 Trigger Hold Off Time
The trigger hold off time indicates how long after a trigger
the oscilloscope waits until the trigger system is ready
again. The trigger system is active again only after the
trigger hold off time has expired. This allows the function
to guarantee stable triggering in case unwanted events are
triggered. Ideally, the hold off time is used to trigger on
periodic signals with several slopes.
HOLD OFF is a dual soft menu key. If the top section of the
soft menu key is active (highlighted in blue), a value can
be entered in the CURSOR/MENU section via universal
knob or numerically via KEYPAD button. You may enter
any value between 50 ns and 10 s. The bottom section of
the soft menu key OFF (highlighted in blue) allows you to
deactivate the function HOLD OFF.
6 .4 Trigger Events
Use the UTIL menu in the VERTICAL control panel on page
2|2, and then choose the soft menu key ACQ. TRIGGER
EV. to issue a pulse at the AUX OUT connector for each
trigger event (Issuing The Trigger Frequency).
6 .5 External Trigger
The settings for the external trigger input (EXT TRIG IN)
can be set via the POD menu. After pressing the POD but-
ton you can activate resp. deactivate the external trigger
functionality (soft menu key EXT). If the external trigger
functionality is activated (ON), the settings for the external
trigger functionality can be set via MENU menu in the
VERTICAL section of the front panel. Via soft menu key
EXT. THRESHOLD the threshold for the external trigger si-
gnal can be set. You can use an external trigger signal e.g.
for CS (Chip Select) of a SPI BUS (displayed as green line).
Changing the time base does not impact the selected hold off
time.
Fig. 6.6: External trigger signal
