Sequence. Use the A Trigger Event with the B Trigger Event to capture complex data. Both the A and B trigger events must be edge
triggers and rising or falling slopes.
• Time. After the A Event occurs, the trigger system waits the specified amount of time, and then looks for the B Event before triggering
and displaying the waveform.
• Events. After the A Event occurs, the trigger system looks for a specified number of B Events before triggering and displaying the
waveform.
Video Trigger on specified fields or lines of a composite video signal. Only composite signal formats are supported. Trigger on NTSC, PAL,
or SECAM. Works with Macrovision signals. Trigger on a variety of HDTV video standard signals, as well as custom (non-standard) bilevel
and trilevel video signals with 3 to 4,000 lines.
Bus. This trigger is used with both analog and digital signals to set up parallel buses or serial buses. A bus trigger event occurs when the
instrument detects a bus pattern that you specify for a parallel bus, or a bus cycle you select for a serial bus. A bus is defined in a bus
menu. Serial buses are optional, see
Serial bus decode and trigger options
Trigger modes
The trigger mode determines how the instrument behaves in the absence of a trigger event:
• Normal trigger mode enables the instrument to acquire a waveform only when it is triggered. If no trigger occurs, the instrument does
not acquire a waveform, and the last waveform record acquired remains on the display. If no last waveform exists, no waveform is
displayed.
• Auto trigger mode enables the instrument to acquire a waveform even if a trigger does not occur. Auto mode uses a timer that starts
after a trigger event occurs. If another trigger event is not detected before the time out, the instrument forces a trigger. The length of
time it waits for a trigger event depends on the time base setting.
Auto mode, when forcing triggers in the absence of valid triggering events, does not synchronize the waveform on the display. In other
words, successive acquisitions are not triggered at the same point on the waveform; therefore, the waveform will appear to roll across the
screen. If valid triggers occur, the display will become stable.
Trigger holdoff
Trigger holdoff can help stabilize triggering. When the instrument recognizes a trigger event, it disables the trigger system until acquisition
is complete. In addition, the trigger system remains disabled during the holdoff period that follows each acquisition. Adjust holdoff to obtain
stable triggering when the instrument is triggering on undesired trigger events.
A digital pulse train is a good example of a complex waveform. Each pulse looks like any other, so many possible trigger points exist. Not
all of these will result in the same display. The holdoff period allows the instrument to trigger on the correct edge, resulting in a stable
display.
At the longer holdoff time for the top waveform, unstable triggering occurs. With a shorter holdoff set for the bottom waveform, triggers all
occur on the first pulse in the burst to remedy the unstable trigger.
Triggering concepts
3 Series Mixed Domain Oscilloscope Printable Help
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