Copyright © 2005 Data Design Corporation Version 05.02.06
All rights reserved.
12
In oscilloscope mode the trigger controls mirror those on an oscilloscope. The trigger
Source can be either channel or the external trigger input. The trigger Slope can be rising or
falling edge. The trigger system can operate in a Mode of
AUTO, NORMAL, or SINGLE which
mirror their oscilloscope equivalents. The NORMAL mode will record and display new
information only after receiving a trigger event and again after each subsequent trigger event
following complete display of the data from the previous event. The SINGLE mode will display
information only from the first such event after which the Run/Stop control in the lower right
corner of the screen will be set to STOP. Data from an additional trigger event can only be
recorded by clicking on the Run/Stop control to set it back to RUN. The AUTO mode behaves like
the NORMAL mode except that the software will inject a trigger if one is not received in an
internally determined time. This trigger will of course not be synchronous with any event in the
input signal but the resulting display can be useful in the event that it is not clear how the trigger
source should be prepared. If a trigger event does occur before the internal timeout on each
cycle, the display will be properly synchronized to this event.
The Run/Stop control can be set to STOP in any trigger mode to cause the software to
ignore any additional trigger events. The display will be a static representation of the last
captured data. When the trigger system is set to STOP in the oscilloscope AUTO or NORMAL
modes, only the data already on the screen will be available. When the SINGLE trigger mode sets
the control to STOP, the entire memory is available for review. This distinction relates to the
ongoing recording operations in the other modes. That is, the SINGLE mode does not record pre
trigger samples for an anticipated subsequent trigger while the other modes do, which would of
course overwrite data from any previous trigger. When switching between trigger modes, the
Run/Stop control is automatically returned to RUN to avoid the typical need to do this manually.
The analog voltage threshold at which a trigger is detected is called the trigger level. For
the external trigger input, this level is adjustable in an absolute range of –10V to +10V using the
Ext Level control. If the trigger source specifies that one of the channels should be used, the
range becomes somewhat larger than the full scale analog input range. The location of the
trigger threshold will be indicated in an abstract way with an arrow on the right side of the
oscilloscope display with the color of the selected source channel. The level can be adjusted by
clicking the left mouse button on the oscilloscope screen within the far right horizontal division.
The trigger threshold will be moved to the location of the mouse cursor. The location can be
dragged by holding the left mouse button down while moving the mouse. If the offset were to be
adjusted, the trigger location will be further adjusted with it to keep the intended trigger
threshold with respect to the new zero volt line. This may force the trigger location off the
screen, which will be indicated by a vertical pointing arrow at the far left top or bottom of the
screen. This is the benefit of a trigger range greater than the full scale analog input range.
The Force Trigger button allows the user to issue a software trigger at any time in any
mode. This function is independent of anything else in the software. If the instrument and
software are configured to respond to a trigger, clicking this control will cause it to act the same
as if the trigger had come from the specified source. Of course there is no way to synchronize
this action to any event, but this control can be useful in performing setup operations,
particularly in transient recorder mode.
Finally, the Center Trigger button automatically returns the display settings so that the
trigger event is displayed at the horizontal center line of the gradicule. This can be useful when
exploring the outer reaches of the recorded time in any mode and it is desired to return to time
zero, the time of the trigger event.
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