Chapter2 HardwareOverview
NI5911 User Manual 2-12 ni.com
TriggerHold-Off
Thetrigger hold-off is a length of time that th eN I59 11 waits after a trigger
isaccepted before it accepts another trigger. In other words, when a trigger
isreceived during acquisition, the trigger counter is loaded with the desired
hold-off time. Hardware then rejects all triggers until the counter has
expired or the current acquisition completes, whichever is longer.
Note Thet ime the acquisition takes to complete from the time a trigger occurs is
(posttrigger samples)/(sample rate (megahertz)). If this time is larger than the trigger
hold-offtime, the trigger hold-off has no effect because triggers are always rejected during
acquisition.
Triggerhold-off is provided in hardware using a 32-bit counter clocked
bya 25 MHz internal tim ebase. Withthis configuration, you can select
ah ardwareho ld-offvalue of 40 ns to 171.8 s in increments of 40 ns.
Figure 2-8 showsa timing diagram o f signals when hold-off isen abled
and the hold-offtime is longer than posttriggered acquisition.
Figure2-8. Timing with Hold-Off Enabled
Trigger
Hold-Off
Acquisition
InProgress
Pretrigger
Data
Posttrigger
Data
Hold-OffTime in nanoseconds
(Adjustablebetween 40 ns and 171.8 s)
=Trigger Not Accepted
=Trigger Accepted