ADLINK Technology NuDAQ PCI-9812/10 User Manual

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ADLINK Technology NuDAQ PCI-9812/10 User Manual Manual pdf 35 page image

Operation Theorem • 275.3 A/D Trigger Source ControlPerforming the trigger acquisition in PCI-9812/10, the followingitems have to be specified before DMA operation starts:l clock source: refer to section 5.4l clock rate: refer to section 5.4l trigger source: refer to section 5.3.1.l trigger level: The trigger event occurs when the triggersignal crosses the specified trigger voltage. Please refer tosection 4.5 for the relationship between the 8-bit triggerlevel and the trigger voltage.The trigger is detected while the trigger event occurs. For Post-trigger and Middle-trigger, the data acquisition is performed after thetrigger event; however, the time when the AD conversion starts is350 ns slower than the time when the trigger is detected. This350ns delay will have minor effect for high speed data acquisition.l trigger polarity: trigger slope. This ‘0’ value means positivetrigger and the ‘1’ value means negative trigger.l trigger mode: refer to section 5.3.2.5.3.1 Trigger SourcesInternal TriggerAn internal trigger is a software trigger. The trigger event occurswhen you call _9812_AD_DMA_Start( ) function to start theoperation.External Analog TriggerYou can use the signal on any analog input channel (CH0, CH1,CH2, or CH3) as the trigger signal for external analog trigger. Thetrigger conditions for analog triggers are described as follows:l Positive-slope trigger - The trigger event occurs the firsttime the trigger signal (analog input signal) changes from avoltage that is lower than the specified trigger level to avoltage that is higher than the specified trigger level.l Negative-slope trigger - the trigger event occurs the firsttime the trigger signal (analog input signal) changes from avoltage that is higher then the specified trigger level to avoltage that is lower than the specified trigger level.